H a n d b o o k

MushroomIntegratedPestManagement

P E N N S Y L V A N I A

The PA IPM Program is a

collaboration between the

Pennsylvania Department of

Agriculture and The

Pennsylvania State University

aimed at promoting

Integrated Pest Management

in both agricultural and

nonagricultural settings.

College ofAgriculturalSciences

This publication was developed by the PA IPM program with the cooperation of the AmericanMushroom Institute.

Table of Contents

I. Theory of Integrated PestManagement 5

A. History, Definitions, and theEconomic Threshold 6S. Fleischer

B. Pesticides and Resistance inIPM 13S. Fleischer

II. Integrated Pest Manage-ment in MushroomProduction 20

A. Specific Control Techniques

1. Exclusion 21P. Coles

2. Cultural Control 27P. Coles/W. Barber

3. Biological Control 33D. Rinker

4. Chemical Control 37P. Coles

B. Pesticide Safety 43S. Whitney

C. Pest Species Biology andControl

1. Arthropod Pests 47C. Keil

2. Fungal Pathogens 52P. Coles/W. Barber

3. Weed and Indicator Molds 61D. Beyer

4. Bacterial Diseases 75P. Wuest

5. Nematodes 78P. Coles

6. Virus Disease 85P. Romaine

Introduction 4P. Coles

In this handbook we have addressed themost important pest organisms with thepotential to reduce mushroom yield andquality. The handbook is intended forgrowers, as well as researchers, as bothan educational tool and a referencemanual. Recommendations presentedhere are not intended to bind growers intheir decision-making processes. Rather,they should serve as a guide for develop-ing effective Integrated Pest Manage-ment (IPM) programs. Each growershould develop specific operatingprocedures and checklists specificallytailored for individual use. In addition,as technology is always changing, thishandbook will be updated periodically.

The handbook is divided into two parts,covering the theory of IPM and thepractical aspects of IPM in mushroomgrowing. The theory section definesIPM and gives it historical perspective.It also explains the concepts of pestmanagement and types of control, andthe importance of understanding pestlife cycles and biology. The section onIPM in mushroom growing describeshow unique features of mushroom cropscan be used effectively in IPM, and howthe theory of IPM can be appliedeffectively.

Mushroom growing lends itself natu-rally to IPM. It is one of the few formsof agriculture in which the crop isgrown inside climate-controlledbuildings. This offers two advantagesnot available to most other crops. First,control of the internal environment ofthe growing room provides an impor-tant weapon against many pests.Temperature and humidity manipula-tions, for instance, are two of manycultural options available in mushroompest control with IPM. Second, sincethe crop is grown indoors, pests can beexcluded. This control measure isunavailable to farmers of field crops,who have little control over pestinvasion. An effective IPM programtakes advantage of these particularcharacteristics of mushroom growing.

Other features of mushroom productionmake IPM a necessity, not an option.With production measured in poundsper square foot rather than in bushels ortons per acre, mushroom growing isvery dense farming. If a pest gets into aroom, it can spread rapidly because ofthe large amount of food availablewithin a relatively small space. Inaddition, many pests cannot be con-trolled using chemical pesticides, eitherbecause there are no products labeledfor mushroom use, or because materialsdon’t even exist for a specific type ofpest organism. Increased regulations aredriving up the cost of producing newpesticides, making it difficult orimpossible for chemical manufacturersto invest in a minor-use crop likemushrooms. Usually, we are forced torely on pesticides developed for othercommodities. An IPM program thatexcludes pests and takes advantage ofthe ability to manipulate the growingenvironment not only is a more effectivemeans of pest control but also allowslimited dependency on chemicalpesticides.

These features make the IPM approachthe most effective and economicalmeans of long-term sustainable pestcontrol. Anyone trying to control pestswithout IPM eventually will end up atthe mercy of those arthropods andmushroom diseases. We hope thismanual will help you avoid that fate.

Introduction

4

I.Theory ofIntegratedPestManagement

5

History, Definitions, andthe Economic Threshold

Vernon M. Stern was working for theWestside Alfalfa Pest Control Associa-tion in the San Joaquin Valley, Califor-nia, a big association of growersinvolving 10,285 acres when it formedin 1945. The association was organizedto help decide when to apply insecti-cides against the alfalfa butterfly.

The alfalfa butterfly was not the mostserious pest in alfalfa, but at times itflared up and caused very serious loss.Alfalfa growers had materials likecalcium arsenate at their disposal, andthey used these materials frequently, butat significant expense and with hardwork. The growers formed an associa-tion after entomologists showed that aparasitoid controlled the butterfly mostof the time, and that growers couldmake many fewer pesticide applicationsif they could estimate how well theparasitoid was controlling the butterflylarvae early in the crop growth cycle.The association hired people to do thefieldwork and calculations and to giveadvice. The Westside Alfalfa PestControl Association called this “super-vised control.” The system was success-ful, and soon the Westley Pest ControlAssociation and the Tracey Pest ControlAssociation formed in other parts ofCalifornia.

These efforts at supervised controldeclined rapidly when DDT and othernew insecticides came into use. By thelate 1940s, over 90 percent of acreagewas treated with new materials, calciumarsenate fell into disuse, and the PestControl Associations disappeared. Thenew materials worked well for less cost,so Vernon M. Stern went to graduateschool with Ken Hagen, the first personin charge of the Westside Association,and Robert van den Bosch, who hadalso been in charge of the Associationfor a period of time. They worked withProfessor Ray F. Smith, who hadinitially organized the Pest ControlAssociations.

It was not long before another insect,the spotted alfalfa aphid, came into theSan Joaquin Valley, and by 1955 thisaphid was resistant to pesticides. Smithand his students (Stern, van den Bosch,and Hagen) imported an exotic parasi-toid and studied native predatoryinsects. Both the parasitoid and thepredators were effective when notdestroyed by pesticides. They thenfound insecticide materials and usepatterns that were relatively selective,allowing the natural enemies to coexistwith the valuable insecticide tools.

A. History, Definitions, and the EconomicThresholdShelby J. Fleischer

Integrated pest manage-

ment is the [information-

based] selection, integra-

tion, and implementation of

pest control based on

predicted economic, eco-

logical and sociological

consequences.

Bottrell, 1979.

Council of Environmental

Quality

6

This “Integrated Control” concept,published in 1959, was quickly ex-panded to include all methods ofcontrol. Thus, the Integrated PestManagement concept was born at least40 years ago. The concept was not bornsolely in California; similar develop-ments were occurring in Arkansas forcotton crops and in Canada for apples.The concept arose from a philosophyfor which the objective is to manage apest population below economicallydamaging levels, and in a way that ispractical for growers, by integratingmultiple control options (see Perkins1982 for a full historical perspective).IPM always has emphasized integrationof control tactics, including pesticides,and monitoring to help determine timeand location for pesticide application.

In 1959 Vernon M. Stern with his co-authors Smith, van den Bosch, andHagen, wrote a paper entitled “TheIntegrated Control Concept,” (Stern etal. 1959) in which they generalizedabout integrating biological controlsand insecticides. To make this work,they discussed monitoring, whichrequires understanding of sampling andmeasurement of pest density. Theynoted how pest populations fluctuateover time. By monitoring density, theyargued, intervention with pesticides canbe limited. This practice limits chemicalapplications to those necessary timesand places where other tactics are notsufficient.

So when does it become necessary tointervene with pesticides? In manyrespects, this is an economic decision. Itrequires relating economics or commer-cial goals of production to fluctuatingpest density. Simply defined, the time tointervene with a pesticide is when theexpected gain from using the pesticideequals the costs associated with its use.The pest density at which the gainequals the cost is the Economic InjuryLevel. Thus, IPM relates pest popula-tion dynamics to commercial produc-tion goals.

The concept of economic injury level isshown in Figure 1. (Similar figures canbe found in Stern’s paper, publishedabout 40 years ago, and similar conceptswere in use in cotton production almost75 years ago.) The figure shows that thepest density is changing over time. Atlow densities, the costs of the damagedone by the pests are less than the costsof control, so it does not pay for themanager to add the control. At higherdensities, however, it does pay tocontrol. Pest density is dynamic, andmanagers can make short-term predic-tions about what the density soon willbecome. Managers usually want or needto implement controls a short timebefore the Economic Injury Level isreached. The Economic Threshold is thedensity at which controls are added. It isset so that, if controls are applied andare effective, the Economic Injury Levelis not reached.

Figure 1. Graph of economic injury level.

Pes

t P

op

ula

tio

n

Time

Economic Injury Level

Pays to Control

Does Not Pay to Control

7

Today, there are many definitions ofIntegrated Pest Management. They allrecognize that many factors influencepest dynamics, the way these dynamicsrelate to production agriculture, and theneed to integrate multiple controlstrategies to manage pests over a longtime frame. IPM has foundations inecology—an understanding of therelationships of the pest and beneficialorganisms within the biotic and abioticenvironment, and an understanding ofthe distribution and abundance of theseorganisms. IPM emphasizes creatingconditions to preclude an organismfrom reaching pest status, correctlydiagnosing and monitoring pestpressure, and allowing natural mortalityfactors to work as well as possible. IPMis a philosophy, a way of thinking, anattitude, which is adapted in practice tomeet economic realities of commercialproduction and modified as thoserealities or tools available for manage-ment change. A slightly modifieddefinition of IPM from the Council ofEnvironmental Quality is “. . . the[information-based] selection, integra-tion, and implementation of pestcontrol based on predicted economic,ecological and sociological conse-quences” (Botrell 1979).

Problems With Pesticide Overuse

Over time, well-documented problems with sole or over-reliance on pesticideswere discovered, and they still are being discovered. Use patterns, rates, timing,and other aspects of pesticide application are designed to minimize theseproblems. Pesticides are an important part of IPM, but not the only part, andthey require a good understanding to be used well. To ensure safety and conductbusiness legally, it is essential to follow the label and to realize that changes tolabels occur frequently. Information for pesticide use is printed on the label,which is a legal document, and must remain with the pesticide container. Over-reliance on pesticides has been linked to problems, including:

ResistanceA change in the genetics of the pest population that impairs control in the field.

Depletion of natural controlsMortality of predators or parasitoids, which results in pests reaching even higherdensities (called resurgence) or species that were not previously pests reachingpest status (called secondary outbreak).

BiomagnificationA build-up of the pesticide in fatty tissue, followed by an increase in the concen-tration of the pesticide in organisms higher on the food chain, includinghumans.

Environmental contaminationUnacceptable levels of the pesticide in groundwater, or in parts of the environ-ment where pesticides were never meant to be.

Species displacementA change in the biodiversity of an area caused by the effect of pesticides onspecies populations.

Endocrine disruptionPesticide (and other) molecules acting upon the hormonal system of animals andhumans, affecting their development and immunological processes.

Human health dangerDirect or chronic toxicity to applicators or manufacturers; or to consumerscaused by unacceptable residues in food.

8

An IPM Philosophy inMushroom Production

IPM in mushroom production got itsstart when sciarid fly populations beganto explode in the late seventies as theresult of environmental changes broughton by the availability of air condition-ing. Before air conditioning, mush-rooms were produced only in the coolseason. When crops were most suscep-tible to infestation, it was usually toocold outside for wild populations to bemobile, thus they were not able to entergrowing rooms. Also, the summer was abreak in the growing cycle, and thusalso a break in the life cycle of sciaridflies within mushroom houses.

With the advent of air conditioning,there was no longer a break in thegrowing cycle, and sciarid flies were ableto breed uncontrollably. Despite the useof chemical pesticides, the flies werewinning the battle. By the summer of1978, fly populations in Chester andBerks Counties in Pennsylvania werecausing severe crop loss.

The Pennsylvania State Universitybegan an interdepartmental IntegratedPest Management program for themushroom industry in early 1979. Thegoal of the program was to reduce pestpopulations in an ecological way toeconomically tolerable levels. Theprogram was to study four majormushroom pests and diseases: thesciarid fly, Lycoriella mali (Fitch); thephorid fly, Megaselia halterata (Wood);Verticillium or dry bubble, Verticilliummalthousei; and bacterial blotch,Pseudomonas tolaasi. The most impor-tant components of the program weremonitoring and identifying pests anddiseases. Mushroom pest adults as wellas larvae and eggs were monitored andidentified, and mushroom beds weresampled for diseases so their life cyclescould be studied.

We easily can recognize an IPMphilosophy in past and current manage-ment of pests in mushroom production.Management tactics are related to thebiology and ecology of pest species andthe relationship of the pests to yield,quality, or marketability of the crop.There are a variety of tools in mush-room production that influence pestdensity and dynamics. These are notmutually exclusive, and are best inte-grated so that one tactic helps another.Many specific strategies with specificpests are discussed in the followingchapters, but it is worth pausing toconsider general terms that classifycontrol strategies and their relevance tomushroom production:

ExclusionTechniques that help prevent the pestfrom reaching sites where it can createdamage, such as sealing walls andcracks, to prevent entry of flies. Airmust be filtered before it enters therooms. Any personnel or equipmententering a room must be clean and/orsanitized.

Delaying accessTechniques that slow the rate at which apest reaches sites where it can createdamage. Examples include maintainingsanitation in the premises aroundmushroom growing houses and keepinggrass cut and trees trimmed.

Cultural controlGrowing techniques that make theenvironment less supportive of pestsand more supportive of beneficialorganisms. Composting is an excellentcultural IPM technique that stronglyinfluences fungal competitors andpathogens. Instigation of shorter cropcycles is another IPM tool that stronglyinfluences pest population dynamics.Also important is maintaining anenvironment, including proper tem-perature and relative humidity, thatfavors mushroom growth over itscompetitors’.

SanitationHere’s where mushroom growers canexcel compared to many other agricul-tural production systems. The con-trolled environment required formushroom production allows for use ofsteam-pasteurization at the beginningand end of the crop, and sanitation ofthe growing rooms and equipment.

Biological controlInfluencing the density or activity ofbeneficial organisms, either throughcultural management or inundativerelease of additional beneficials into theenvironment. Composting techniquesinfluence biological control of fungi.Purposeful release of Pteromalidparasitoids on the composting wharf, orentomopathogenic nematodes, areexamples of inundative release ofbeneficials used in mushroom produc-tion.

Chemical controlIntroducing chemicals to kill pests. Thetypes of chemical tools available arechanging rapidly, and mushroomgrowers have kept up with this change.Compare, for example, the types ofmaterials listed in Duffy 1981 withFleischer and Keil 1994. The 1970srelied on broad-spectrum materials thathad activity against a wide range ofinsects; the 1990s relied more on insectgrowth regulators that have muchgreater selectivity and are more precisein what they target. This trend ofgreater selectivity can be expected tocontinue. In an IPM program, thesechemical tools are used in a way that isas compatible as possible with the othertools listed above, as well as withpesticide resistance management, whichis discussed later in this chapter.

9

Biorational materialsSynthesized or extracted compoundsthat are applied to manage pest densi-ties, which often have much greaterselectivity upon target pests. Examplesused in mushroom production includeinsect growth regulators, botanicalextracts, and microbial metabolites.

Clearly, mushroom growers can and dointegrate multiple control strategies, asin an IPM program. Further, there isthe issue of relating decisions to pestpopulation dynamics: the EconomicInjury Level or Economic Threshold.The level of pest density that can betolerated is both a management andsubjective decision. Not every farm isthe same. Both the gain achieved by theuse of the material and the market priceof the mushrooms will vary amongfarms and through the season on a givenfarm. Economic goals also vary: somefarms may emphasize quality factors forselect markets, others may emphasizevolume.

In addition, other biological factorsshould influence management decisionsabout the tolerable levels of a pest. Forexample, if sciarid flies are aidingtransmission of a pathogen or mites,then the tolerable pest density of fliesshould drop dramatically. The tolerablepest density is also different at differenttimes in the crop growth cycle. Thistolerable pest density is best developedthrough experience and in consultationwith others who have had growingexperience.

In an IPM philosophy, growers do notstrive to remove every individual pest atevery moment. Rather, managementinvolves monitoring pest pressure andusing that information to influencemanagement. In mushrooms, monitor-ing includes fly monitors and recordsheets (Figure 2), nuisance fly monitorson the composting wharf, and routineinspection of beds for diseases. Tem-

determines whether or not a pesticide orother management strategy is workingand calls attention to times whenstrategies are not working as expected.Sometimes pest pressure increases after apesticide is applied. Perhaps newimmigrants arrived, or they arrivedmore quickly than anticipated, or astage of the pest that was not susceptibleto the pesticide developed into a stagethat is now a problem. Perhaps the pestpopulation is developing resistance tothe pesticide currently in use. Clearly,monitoring is an essential part of IPM.

It is clear that the philosophy of IPM iscompatible with mushroom production.The Penn State Handbook for Commer-cial Mushroom Growers (Wuest 1992) isfilled with valuable information aboutidentification, diagnosis, culturalcontrols, monitoring, and management.A basic premise is that no single controlmethod will be successful over time.IPM strives to integrate control tactics,which essentially are different types oftechnologies. IPM will use cultural andbiological tactics to the best degreepossible and then include pesticides asneeded. Control technologies discussedin this publication include Diagnosisand Monitoring, Exclusion (ChapterII.A.1), Cultural Controls (ChapterII.A.2), Biological Controls (ChapterII.A.3), and Chemical Controls (Chap-ter II.A.4).

Technologies change over time. Whatmushroom growers may not realize isthat they can be among the best atadapting to these changes. Changes intechnology are true for cultural tech-nologies as well as for biological andpesticide technologies. Consider thechange in growing technology, varieties,and cropping cycles over the last 20years. Because the technologies keepchanging, the IPM program also mustadapt, change, and improve. It is clearthat the IPM philosophy of integrating

peratures are monitored in both Phase Iand II. Though this is not a directmeasure of populations, it is a goodindicator of what is happeningmicrobially; if the compost is cold nearthe center of the pile—for example,120°F (49°C)—it is an indication thatthere are anaerobic organisms producingthe wrong type of compounds. This isnot a direct measure, but it is veryimportant to the quality of the compostand reminds the growers that thecompost is alive, something that usuallygets very little attention.

Rules of thumb provide economicinjury levels for some pests. For ex-ample, fly pressure may be low enoughduring the winter to not requireinsecticides. An economic injury level ofadult sciarid counts per day, as deter-mined on the Pennsylvania MushroomFly Monitor, is shown in Figure 3. Inthis example, there is virtually notolerance for flies before, and 3 daysafter, spawning. After spawning, thethreshold rises to ten flies per strip perday. The threshold rises again slightlysoon after casing and more dramaticallyat pinning. The idea is that flies arrivingearly will cause greater damage and are asign of much greater problems that willoccur before the crop is complete, butflies arriving later will have less opportu-nity to cause damage because they haveless time to complete another life cycle.This specific threshold may not be thebest for your facility, as the croppingcycle and other factors may not beexactly the same, but it does demon-strate that thresholds can influencemanagement and suggests that thresh-olds can be adapted to your farm.

Monitoring is essential for definingwhen and where to invest pest manage-ment inputs. The first step in monitor-ing is identifying the pest and diagnos-ing the problem. Monitoring also isessential for evaluation and follow-up. It

10

Figure 2. Pennsylvania mushroom fly monitor record sheet.

Instructions for use: Record daily fly counts from the monitor for days -6 thru +21 fromspawning. Note whether the flies are cecid (=C), phorid (=P), or sciarid (=S).

Note: A 10x hand lens will be helpful in insect identification.

Pennsylvania Mushroom Fly Monitor Records

Block Number: Room Number:

Number and Number andDay Date Name of Flies Day Date Name of Flies

-6 +8

-5 +9

-4 +10

-3 +11

-2 +12

-1 +13

Spawning +14

+1 +15

+2 +16

+3 +17

+4 +18

+5 +19

+6 +20

+7 +21

11

Phorid Fly Sciarid FlyCecid Fly

multiple management tactics andallowing pest density dynamics toinfluence management is well embed-ded in the modern mushroom farm.

In subsequent chapters, note how oftena range of management options arediscussed and how these options requirean understanding of the life cycle of thepest and an understanding of how thepest interacts with the biotic and abioticenvironment (in other words, theecology of the organism). In the future,new technological options will become

available, and IPM is a philosophy thatcan integrate and prioritize theseoptions. Fundamentally, an IPMprogram identifies and monitors thepest, takes advantage of the options thatmanage the pest through culturalmeans, and adds pesticides whenneeded. The new pesticides will bringimproved safety and environmentalprofiles. To be preserved, they should beimplemented in conjunction with apesticide resistance managementprogram.

Figure 3. Pennsylvania mushroom fly monitor action levels. Adult sciarid flycounts determine the need for insecticide applications in a growing room.

Nu

mb

er o

f In

sect

s p

er S

trip 20

10

0Days-3 -1 1 3 5 7 9 11 13 15 17 19 21

▲ ▲Spawning

▲Casing Pins

Selected References

Bottrell, D. R., Council on Environ-mental Quality. 1979. Integrated PestManagement. U.S. GovernmentPrinting Office 286-007/6007.

Duffy, M. D. 1981. Mushroom Inte-grated Pest Management and the Cost ofCurrent Management Techniques. M.S.Thesis. The Pennsylvania State Univer-sity.

Fleischer, S. J. and C. B. O. Keil. 1994.Insecticide priorities in the U.S.mushroom industry. Mushroom News42: 7–10.

Perkins, J. H. 1982. Insects, experts, andthe insecticide crisis. The quest for newpest management strategies. PlenumPress. New York. 304 pp.

Stern, V. M., R. F. Smith, R. van denBosch, and K. S. Hagen. 1959. Theintegrated control concept. Hilgardia29: 81–100.

Wuest, P. J. (ed). 1992. Penn StateHandbook for Commercial MushroomGrowers. The Pennsylvania StateUniversity.

12

Changes in technology are easy to see.What may not be as obvious is that thepests themselves keep changing. Perhapsthe most important change is thedevelopment of resistance. In manyagricultural systems, resistance has beenthe single most important factor causingthe decline of a pest managementstrategy.

Resistance is a genetic change, occurringin response to selection by toxicants,that may impair control in the field.Pests can withstand toxins to somedegree, often in relation to the dose towhich they are subjected. There isvariation in this ability to detoxify; thatis, some individuals can detoxify moreeasily than others. Pesticides are onetype of toxin, and when they areapplied, individuals in a population arekilled. If individuals with improvedways to detoxify exist, selection forthose individuals will inadvertentlyoccur. They will survive and reproducemore easily than other indiviuals in anenvironment that includes the pesticide.This process is known as selection forresistant individuals by the toxicant.Continued selection will result in aresistant population. This is evolution inaction, and it is the same process thatresults in strains of human pathogensbecoming resistant to antibiotics.

Evolution of resistant pest populationsis a common fact of agriculture today.Over 500 pest insect species haveevolved resistance to at least one

pesticide during the last 40 years(Georghiou and Taylor 1986). Theincrease in numbers of resistant specieshas been exponential for these last 40years. More recently, the increase inresistant populations of pathogens andweeds are beginning to follow the samecurve. It should come as no surprise,therefore, that resistance in mushroompests is now well documented. Ex-amples include sciarid flies, which areresistant to pyrethroids (Keil andBartlett 1996); house flies and stableflies on the composting wharf, whichare resistant to many classes of insecti-cides; and verticillium, which is resistantto benomyl.

Resistance must be evaluated withrespect to the natural variation amongindividuals and populations in theirabilities to detoxify a pesticide. It can bea matter of opinion as to when to label apopulation as resistant, and when it isjust displaying natural variation. TheWorld Health Organization has set astandard of 10; that is, when a popula-tion requires 10 times the amount ofpesticide to kill 50 percent of a testpopulation compared to a referencesusceptible population, it is classified asresistant. Also, it is very common forpopulations to exhibit different abilitiesto withstand pesticides in differentgeographic areas. Thus, a pest may beresistant in only certain, often small,geographic areas. With this in mind, italso is possible to recognize limitedresistance of sciarids to diflubenzuron.

B. Pesticides and Resistance in IPMShelby J. Fleischer

13

Resistance Management

The realistic potential for resistance is apredictable, evolutionary consequenceof pesticide use (and other managementtactics as well). Therefore, resistancemanagement is now considered andmust be a part of integrated pestmanagement. As a new managementtactic such as a new chemical is de-ployed, it should be used in a mannerthat is designed to prevent or slow thedevelopment of resistance. This isbecoming especially important as wemove to the use of newer, selectivematerials. The goals of resistancemanagement are to avoid resistance,slow the rate of resistance development,and cause resistant populations to revertto more susceptible populations.

To best understand resistance manage-ment, it is helpful to understand thedetails of the evolutionary process thatresults in resistance. When measuringsomething about an individual, such asits ability to withstand a pesticide, youare describing its phenotype. Whenmeasuring phenotypes for a populationof individuals, the phenotype of thatpopulation can be described (forexample, you may observe that 20percent of a population withstands aspecific dose of a specific pesticide).With resistance, we observe reducedrates of mortality (lower efficacy) whena pesticide is applied.

Lower efficacy can be due to manycauses. In fact, in most cases in agricul-tural settings, lower efficacy is caused byapplication, timing, or something that isnot related to resistance. However, whenlower efficacy is caused by a change inthe proportion of the pest populationthat carries a heritable genetic compo-nent such as DNA, then lower efficacyis due to resistance.

Mutations cause the variation of DNAamong individuals. Mutations are rare(perhaps one in a million at a givensite), but they are present. For example,if mutations occur at a rate of one in amillion at a given site on a long strandof DNA, and there are 100 million suchsites in the DNA of a human, thenthere are about 100 mutations occurringin each human. In DNA, which codesfor protein, mutations result in differentversions of the same protein. Mostmutations have either no effect or areharmful. Some, however, producebeneficial results; some proteins provideindividuals with improved abilities tosurvive and/or reproduce.

Principles of ResistanceManagement

When a pesticide with a new mode ofaction is introduced into commercialuse and gains acceptance, it can beassumed that it is effective. At thatpoint, it kills the target pest, andresistance is not a problem. What hasbeen learned from many experienceswith pests that have evolved resistance isthat alleles (segments of DNA that codefor protein) that confer resistance areeither not present or are present at verylow frequencies when the new materialfirst is used. These low frequencies areoften lower than can be measuredeconomically. For the purposes of thisexercise, assume that resistant alleles arepresent in less than one in 100,000individuals.

When this same pesticide is observed bya grower to be not as effective as it usedto be, and assuming that everything elseis the same, then resistance is probablyoccurring. By that time, enoughindividuals are carrying resistant allelesto make it visible to a grower. For this tohappen, the resistant individuals wouldhave to occur reasonably frequently; for

example, one in 1,000 individuals nowwould be surviving the pesticidetreatment. That represents a 100-foldincrease in the frequency of resistantindividuals! The key to effectiveresistance management is to start aresistance management program early.Do not wait until field failures becomeobvious; by that time, a dramaticincrease in the frequency of resistantalleles has already occurred. The besttime to design a resistance managementprogram is before a new product is everused.

Crop protection companies are antici-pating the evolution of resistance totheir new materials and are providingresistance management programs as partof the initial introduction of a newmaterial. In some cases, companies aremonitoring for resistant alleles at thetime of introduction, with sensitivitythat would detect the very low levelsexpected in the early stages of resistancedevelopment. Pesticide ResistanceManagement (PRM) is becoming a partof IPM.

14

exceptions are important because theylead to stable resistance. However, in thepresence of the pesticide, the R alleleconfers an advantage to individuals thatcontain it. Over time, the R allele isbalanced with other alleles so that itmay no longer be deleterious.

Biological and ecological factors refer tothe biology and ecology of the pest.Reviews of the many pest species thathave evolved resistance have shownsome clear patterns. One importantexample is generation time. Pests thatquickly speed through one generationafter another have a much greaterpotential of evolving resistance inresponse to selection by pesticides thanpests with slower generation times.Similarly, pests that have a high repro-ductive potential—each female generat-ing many offspring that survive longenough to reproduce—evolve resistancequicker. Immigration traits also areimportant, but tend to work in theopposite direction. Pest species thathave higher rates of immigration tend tohave slower rates of resistance, becausethe constant flow of S alleles into thepopulation serves as a resistancemanagement tool. Those species withlow rates of immigration have greaterchances of RS or RR individuals matingwith each other, which rapidly increasesresistance.

The host range of the pest also hasshown a trend. Pests that have popula-tions spread out among many hosts(polyphagy) tend towards lower rates ofresistance than those that specialize onone host. This is because there is atendency for patches of pest populationsto exist on untreated areas, or refuges,and susceptible individuals existing inuntreated refuges serve to maintain Salleles. Pests that have many matings(polygamy) also tend toward lower ratesof resistance, because there is less chancefor RR individuals to occur.

Factors AffectingResistance Management

The development and rate of resistanceare affected by genetic factors, biologicaland ecological factors, and operationalfactors-activities performed within andsurrounding a production facility(Georghiou and Taylor 1986).

Genetic factors refer to the genetics ofthe pest itself. Does the capacity forresistance exist? Do some individuals inthe population have alleles that code forproteins that confer resistance? Do somedetoxification proteins of some indi-viduals work faster? Do some havethicker cuticles that slow the rate ofpesticide entry? Genetic factors vary—pests do have mutations—and it ispossible, although rare, that a newmutation will confer resistance. Forpurposes of long-term resistancemanagement, it should be assumed that,at some level, resistant alleles arepresent. For the purpose of the follow-ing illustration, we will indicate resistantalleles, pieces of DNA that code forproteins that confer resistance, with acapital “R.” Susceptible alleles will beindicated with a capital “S.” Most insectpests have two copies of each allele, sothey may be indicated by “RR,” “RS,”or “SS.”

So what is the frequency of resistantalleles—what is the percent of thepopulation that displays resistance? Thehigher the frequency, the higher the rateof development of resistance. The Rallele is mixing every time an insectmates. If RR individuals mate with SSindividuals, offspring will be RS,helping to dilute the R allele. Possiblecombinations include:

When a pesticide is introduced intoeffective commercial use, pest individu-als are almost entirely of the SS type. Asresistance develops, some RS becomepresent (from one in 100 to one in10,000), and there are many, manyfewer RR (from one in 10,000 to one in100,000,000). Even if R alleles arepresent, it is desirable to keep many SSindividuals nearby and mating, slowingresistance development. So if thepopulation can be swamped withsusceptible individuals, resistance can beslowed. This is important, because mostof the population (say, from outside themushroom house) consists of suscep-tible individuals (SS) during early stagesof resistance. In the early stages ofresistance, the very rare RR individualmight have a greater chance of drown-ing or desiccating—or dying from anynumber of causes—than mating. After apesticide application, some individualswith R alleles may survive, but somewith S alleles might also (they may havebeen in a protected growth stage, likethe egg stage, and may not have beenaffected). As long as we can keep thefrequency of R low, we have an effectiveresistance management program.

With few important exceptions, the Rallele probably is mildly deleterious. Forexample, it may mildly reduce fecun-dity, at least initially, in the absence ofthe pesticide. The initial R frequency isheld in check by a balance betweenmutation and selection, although

RR with RR to give RR

RR with RS to give RR and RS

RR with SS to give RS

RS with RS to give RR, RS, and SS

SS with RS to give SS and RS

SS with SS to give SS

15

Operational factors are under thegrower’s control. These include thetiming and dose of a pesticide, choice ofmaterials, decisions about tank mixing,and decisions about alternating prod-ucts. Dosage, or application rate, oftendetermines if an individual is susceptibleor resistant. At some very high doselevel, every individual will be killed, andat some low dose level all individualswill survive, regardless of whether theycarry R or S alleles. Measurement of therelationship between dose and mortalityis a dose-mortality curve. The dose-mortality curve shows the proportion ofthe population killed on the y-axisagainst the dose on the x-axis. Bychanging the way the numbers arerepresented, we can straighten out thedose-mortality curve into a line. For asingle population, the curve looks likethis:

When resistance occurs, the curvechanges. The measured points don’tmatch the line as well, suggestinggreater variability in the relationship; orthe curve shifts to the right or gets moreshallow, predicting that mortality islower at the same dose, like this:

Thus, one way of monitoring forresistance is to plot the dose-mortalityrelationship from different points intime, or different geographic areas, ordifferent populations. Different popula-tions of SS, RS, or RR individuals willresult in different lines, like this:

Figure 4. Dose-mortality curve.

Per

cent

Kill

ed

0.01 0.1 1.0

Insecticide Dose or Concentration

Figure 5. Dose-mortality curve withinsecticide resistance.

Per

cent

Kill

ed

0.01 0.1 1.0Insecticide Dose or Concentration

Figure 6. Dose-mortality curves forthree populations.

0.01 0.1 1.0

Insecticide Dose or Concentration

Per

cent

Kill

ed

SS RS RR

Figure 7. Dose-mortality curves forthree populations, including selectivedose.

Selective DoseSome killed, some survive

Per

cent

Kill

ed

0.01 0.1 1.0

Insecticide Dose

SSSusceptible

RSMix

RRResistant

The dosage applied determines selectionfor resistance. If the dosage applied ishigh enough, SS, RS, and RR individu-als are killed, and no selection is takingplace—an event that rarely happens inthe real world. Even when it is possibleto apply such a high dose, the pesticidewill decay over time, and new pestindividuals that arrive (either fromimmigration or development fromanother life stage such as an egg) arethen experiencing a reduced dose.

When a dose kills some individuals butallows others to survive, it is called aselective or discriminating dose. A dosethat is able to separate genotypes (RRfrom RS, or RS from SS), is a discrimi-nating dose. This might occur when apesticide is applied to a mixed popula-tion, or it might occur after a pesticidehas been applied and is degrading into alower concentration. Figure 7 shows aselective dose, where SS and RSindividuals are killed but RR individualssurvive.

16

In the example shown in Figure 7, theRS individuals are killed, but at a lowerdose. In the following example (Figure8), selection might kill only SS indi-viduals. This (Figure 8) is the worst-casescenario for resistance management,because there typically are more RS thanRR individuals. When the selection isallowing RS individuals to survive, theR allele will increase more rapidlybecause there are more RS individuals.

These examples also illustrate that thedominance of the R allele—whetherresistance is expressed in RS individu-als—depends on the dose. When thedose is selecting for RR individuals andkilling RS individuals, the R allele isrecessive or not being expressed when itis combined with the S allele. But whenthe dose is selecting for both RR and RSindividuals, the R allele is dominant.The effective or functional dominancevaries under field conditions anddepends on dose.

As can now be seen, populationdynamics and population geneticsinteract. With resistance management,the population of alleles (R and S) andthe population of individuals (thedensity of individuals of each type)must be considered. For example, therecan be an unstable equilibrium, where Ris selected for but not maintained athigh levels. This can occur within alarge population where RR exists at alow level. A discriminating dose selectsfor the RR individuals, but there are fewof them. If high rates of immigrationand mating of SS individuals follow,most of the offspring will be SS and RS,although some RR will occur. Popula-tion density, population genetics, andresistance are fluctuating over time, andresistance management, as stated earlier,is striving to avoid resistance, slow therate of resistance, or cause resistantpopulations to revert to susceptiblepopulations.

Strategies and Tactics ofPesticide ResistanceManagement

Applying the aforementioned theory todifferent strategies can help manageresistance. These strategies have beenclassified as saturation, multiple attack,or moderation, and have been testedwith simulation models and limitedfield experiments in various agriculturalsystems.

Saturation is an effort to preventselection by making sure even resistantindividuals are killed, typically with ahigh dose, and sometimes addingsynergists to block detoxification. It hasbeen dubbed the “high dose, high risk”strategy, and it works well if all pests arekilled every time. To work, it needs tobe started while the initial R frequencyis very low, and not after some concernabout efficacy is occurring. When pestsre-invade, the saturation strategy worksbest when the immigrants are suscep-tible individuals that mate randomlywith the resistant ones, which is difficultto achieve in an environment of highdosage. The saturation model also worksbest on pests with a low reproductivepotential. Also, this strategy has highrisk, because once it fails (when the doseis no longer killing all individuals butallowing some RR, or even worse, someRS, to survive), it will continue to failquickly if it is not changed. It may bedifficult on some mushroom farms todeliver and maintain a sufficiently highdose at all locations that need to betargeted. When using the saturationmodel, it is important to rememberother concerns surrounding use of largeamounts of pesticides.

The multiple attack strategy takes aimat different modes of action withrotations or tank-mixes of differentmaterials. Rotations involve switching

Figure 8. Dose-mortality curves forthree populations, including less-effective selective dose.

Selective DoseSome killed, some survive

Insecticide Dose

Per

cent

Kill

ed

0.01 0.1 1.0

SSSusceptible

RSMix

RRResistant

17

materials for different applications andrequire a good choice of material in therotation. Ideally, any resistant individu-als surviving the first pesticide applica-tion are killed with the second material.As in saturation methods, rotationworks best when started very early, wellbefore field failures are noted. This isbecause the few resistant survivorswould have less chance of mating andproducing offspring that also matewhen their population is very low.When populations are very low, lots ofnatural mortality (drowning, desiccat-ing, disease, etc.) can keep them low.Issues about whether the R allele exists,and whether cross-resistance exists,should influence choice of material. Towork over a long time frame, rotationassumes that the frequency of R to eachmaterial declines while it is not beingused. This may occur when the nextpest immigration is composed mostly ofsusceptibles (see below). Rotation alsoassumes no cross-resistance.

Tank-mixes also combine materials, butat the same time. They are sometimesused to help ensure efficacy. Some arguethat tank-mixes also can be a resistancemanagement tactic. Tank-mixes withmaterials of distinctly different modes ofaction may help ensure that the secondmaterial kills the rare individual that isresistant to one material. However, if afarm starts to tank-mix because amaterial is not working as well as before,it may be too late—the resistantindividual may not be so rare anymore.Tank-mixes also add expense, and ifproblems arise, they are harder todiagnose. If the different materials donot degrade in the same way, the pestsare not really exposed to both materialsat some time after the applications. Insimulation models, tank-mixes workbest when started early, while the Rfrequency for any material involved inthe strategy is low, and when the

frequency of individuals resistant toboth materials is exceedingly rare. Theassumptions are that all individuals aresusceptible to one or both materials, thematerials decay at approximately equalrates, and as in rotation, there is nocross-resistance.

Cross-resistance refers to resistance thatdeveloped against one material alsoconferring resistance to another mate-rial. Cross-resistance has been fairlycommon for some insects and someclasses of modes of action. Cross-resistance has occurred from onepyrethroid to another pyrethroid, fromthe old organochlorines to the newerpyrethroids, and from organophos-phates to carbamates. This is becausethere are some similarities in the modesof action of these materials at themolecular level. To avoid cross-resis-tance, choose materials with distinctlydifferent modes of action. Withinsecticides, current options includeinsect growth regulators, pyrethroids,entomopathogenic nematodes, andprotein crystals from Bacillusthuringiensis. There are new materialswith yet other modes of action in thepipeline as well, including microbialmetabolites that affect GABA receptors,nicotinoid materials, botanicals, andnewer insect growth regulators thattarget different parts of insect develop-ment. Investment in research will helpdevelop these materials for mushroomproduction. All of these have verydifferent modes of action—some arebetter classified as biological controlmaterials, and their integrated use helpsmake clear how pesticide resistancemanagement is consistent with thephilosophy underlying IPM.

Moderation strives to maintain suscep-tible individuals in the population usingall IPM tactics (cultural, exclusion,mechanical, biological, etc.). Modera-tion attempts to preserve susceptibles inthe environment and allow mating ofthese SS individuals with those carryingthe R allele. The goal is to keep the Rallele swamped with S alleles. Growersshould use application timing to try topreserve susceptibles early in theevolution of resistance, so that not everypest individual is targeted at everymoment. Monitoring and timingapplications help preserve susceptibles.Creation of refuges (refugia)—areas thatare not sprayed—also preservessusceptibles. Refugia can be in themushroom house itself or in surround-ing habitat if they contribute to mating.

In many studies, the decay rate ofpesticides has strongly influenced therate of resistance, and fast-decayingmaterials are associated with themoderation management strategy.Materials that decay quickly initiallyhave a high (and hopefully non-selective) dose, killing all genotypes.Then the fast-decaying materials aregone. There is little time during whichthe dose is selective. Materials thatdecay slowly go through a longer timewith a selective dose. In general, slow-decaying materials—those oftencredited with “residual activity”—favorthe development of resistance. They canexhibit selective activity over longertimes and make it harder for immigrat-ing SS individuals to survive and matewith the rare RR individuals that aresurviving. Choosing materials with afast decay rate has worked as a resistancemanagement tactic for house flies.

18

In most field examples to date, pesticideresistance management programs haverequired preservation and mating withsusceptibles. Choice of short-residualmaterials has worked in models and inpractice. Limiting application to specifictimes of season or generations of thepest, or leaving refuges of untreatedareas with immigration of susceptiblesfrom those areas, have been useful andmay require coordinated activities ofneighboring growers. The most impor-tant factors in simulation modelssuggest that resistance is most influ-enced by the reproductive potential ofthe pest; also, that resistance is bestslowed by immigration of susceptiblesand reduction of selection pressure bymaking applications only when needed,carefully choosing the dosage, and usingshorter-residual materials.

One take-home message is that mix-tures, rotations, and saturation allrequire conditions not well met in thefield; reducing pesticide use (via IPM)has proven more productive thanoptimizing pesticide combinations andspatial deployments. Pesticide resistancemanagement has relied on knowing pestbiology and ecology, understandingevolution, and integrating managementtactics. Technologies available for pestmanagement are changing constantly tokeep up with changing conditions forgrowing and marketing the crop andwith changes in the pests themselves. Aresistant pest population is a change inthe pest population. Clearly, pesticideresistance management has a philo-sophical basis and is part of IPM.

19

Selected References

Georghiou, G. P. and C. E. Taylor.1986. Factors influencing the evolutionof resistance. pp. 143–156 in NationalResearch Council. Pesticide resistance.Strategies and tactics for management.National Academy Press. Washington,D.C. 471 pp.

Keil, C. B. O. and G. R. Bartlett. 1996.Permethrin resistance in Lycoriella mali(Fitch) (Diptera: Sciaridae) on commer-cial mushroom farms. Mushroom News44: 8–13.

Roush, R. T. and B. E. Tabashnik, eds.1990. Pesticide Resistance in Arthropods.Chapman and Hall, New York. 303 pp.

Taylor, C. E., F. Quaglia, and G. P.Georghiou. 1983. Evolution of resis-tance to insecticides: a case study on theinfluence of immigration and insecti-cide decay rates. J. Econ. Entomol. 76:704–707.

Integrated

Pest

Management in

Mushroom

Production

II.

20

Exclusion prevents the entrance of pestorganisms into new rooms and theirescape from older ones. The lattershould not be underestimated. Pestpopulations usually are high in olderrooms, and they threaten infestation ofyounger crops if they are not contained.Since mushrooms are grown insideenvironmentally controlled rooms, ourindustry is in a unique position inagriculture: we are able to control pestmovement into and out of growingrooms. This must be exploited fully inany mushroom IPM program. Once aroom is pasteurized successfully, pestswill have to enter in order to become aproblem. If exclusion were completelysuccessful, there would be no need forany other form of pest control for mostdiseases. (Some organisms such as thebacteria that cause blotch are notdestroyed by pasteurization and must becontrolled through other methods.)This is especially true in the wintermonths when pests should be virtuallynonexistent.

Exclusion, like monitoring, is oftendiscarded when another “magic bullet”pesticide comes onto the market. Thepesticide will give good control for atime, then resistance (See Section I.B)will begin to occur, reducing thepesticide’s effectiveness, or worse,rendering the material useless. Exclusionlimits the number of pests exposed to agiven pesticide, thereby reducingresistance.

There are several ways to accomplishexclusion: the integrity of the buildingmust be maintained; openings must besecured (doors, fans for boiler or electricrooms, etc.); air entering rooms must befiltered; and the movement of peopleand equipment must be restricted.

Construction of new growing roomsmust permit easy sealing of the buildingand provide easy maintenance of thatseal. All areas should have easy access.Any areas not exposed for easy inspec-tion can allow openings to formundetected. Moldings along rooflines,for example, can hide cracks betweenthe wall and roof. Sometimes airhandling transitions or ducts are notinstalled tight against the ceiling. Thespace between the duct and ceiling canbe so small that it is impossible to sealthe area where the wall and ceiling joinover the duct. Remember, the extremeenvironmental conditions producedduring a normal mushroom crop,particularly during pasteurization, canbe very stressful on a building. Crackscan develop that were not there duringinspection prior to the crop.

Building materials also are important.Because it is organic and porous, woodcan be a good hiding place for patho-genic organisms. Porous cinder blocksand concrete also provide refuges fororganisms, particularly in the floor,where it is nearly impossible to develophigh temperatures. Consider inorganic,

A. Specific Control Techniques

1. Exclusion

Phillip S. Coles

21

smooth, dense construction materialswhenever possible. Plastic and alumi-num are good choices, though costoften precludes their use. Inorganicinsulation is a must. Sawdust, forinstance, can become a breeding groundfor pest organisms. Cost of materialsmust be weighed against potentialbenefits.

Don’t overlook the obvious entry pointsin any building, such as drain holes(Figure 9) or the webbing in blockwork.Unless the top of the wall is capped,there are thousands of passagewayswithin the wall through which flies canpass.

In an existing facility, mortar and caulkare inexpensive alternatives to chemicalpesticides or crop loss. When a growingroom is empty, inspect for cracks andany other damage that may haveoccurred during the crop. Buildingsexpand and contract from the changesin temperature during the crop. Highhumidity causes wood to swell. Wheredisimilar materials come together, suchas wooden doorjambs against blockwalls, the different expansion rates ofthe materials cause cracks to developbetween them. All of these areas mustbe inspected, sealed as needed (Figure10), and marked off on a checklist. Turnoff the lights inside the room and lookfor light penetration from outside. If agrowing room has a spring roof, thisarea must be checked. Ceilings areespecially susceptible to damage,particularly if the temperatures duringpasteurization are allowed to get toohigh. High temperatures can damageinsulation; sprayed-on polyurethane canbuckle and crack. Nailed insulationsheets can buckle, pulling the nail headsthrough the insulation and leavingaccess holes through which pests canenter. Turn on the lights inside theroom when inspecting a loft area andwatch for light penetration. Pasteuriza-

Figure 9. Drain plugs must be sealed to keep out flies and especially rodents.

Figure 10. Rooms can be sealed with urethane insulation.

22

fibers. The fly will move the fibers backand forth and work its way throughmaterial that looks impenetrable. Onlyby testing the filter material or flynetting can a grower be confident fliescannot get through it.

tion at the end of a crop is also a goodtime to check lofts, since steam willescape through openings in the ceiling.Mark these openings and have themrepaired. This not only will exclude pestorganisms, but will reduce energy costsas well.

Limiting and sealing access doorways isof particular importance. Only one ortwo doors in a plant or any mushroombuilding should be used as entrances.All other doors should be sealed.Doorways used for entrance and exitmust be sealed around the edges, andthere should be a threshold at thebottom to seal the door when closed.Seal these doors with weather-strippingor strips of filter material (Figure 11).Spray the sealed edges with oil oradhesive as an additional barrier againstpest entry. A step mat with a sanitizershould be placed at the entrance tosanitize shoes. Clean the mat regularlyor it could become a source of infesta-tion. It is better to not have any matthan to use a dirty one. Entrance doorsinto the growing rooms should betreated the same way as the entrance tothe hallway or the plant itself. If there ismore than one door into the growingroom, one of them can serve as theentrance and the others can be sealedcompletely. If doors must be kept openfor ventilation during Phase II, theyshould be covered with fly netting orfilter material.

Obviously, filter media must be imper-vious to fly penetration. What may lookimpervious to us may not be to a fly.Flies can get through much smallerholes than their body size suggests.Filter media offer an additional prob-lem. The structure of most filter mediamakes it ideal for collecting dustparticles, but also for active pests, suchas flies, to work their way through it.When a fly comes in contact with filtermaterial, it sees a mass of hair-like

Figure 11. Filter material used to seal doors.

23

Choosing Filter and FlyNetting

Testing can be accomplished in a varietyof ways. First, inspect the material.Holes large enough to permit thepassage of flies may be obvious. Nettingor filter media may be manufacturedinconsistently, allowing some of theopenings to be larger than others, or afilter may have thin areas or “windows”insects can pass through. The materialmay not be strong enough: i.e., peopleworking near netted openings maydamage it too easily.

Second, test the filter or netting for flypenetration. One method to accomplishthis is to wrap the netting or filtermedia in question around a wire frameand place a known number of fliesinside. Seal the material with a twist tieor string and place it outside (where theflies can’t have access to new growingrooms) or inside an old room that hasflies, and determine if they escape.Conversely, you could place somethingthe flies want inside the material anddetermine if they can penetrate it. Tryplacing fresh spawned compost or a flylight equipped with flypaper inside abox to capture invaders. Use an opentopped box with sealed seams and placefreshly spawned compost in the bottomof the box. Place flypaper on the top ofthe compost, sticky side up. Or, attach afly light with flypaper to the bottom ofthe box. Cover the open side of the boxwith the material and seal it with ducttape. Make sure there are no openingsin the box or at the seals where fliescould get through. If a fly light is used,an opening must be made for the powercord. Be certain this is sealed. Put thebox in an old, fly-infested room. If thetest material is impervious to fly entry,no flies should be found on the paper.

There are other considerations forchoosing filter material instead ofnetting for a particular application.With netting, excluding flies is enough,but filters are expected to remove sporesand dust particles. Spores of concern inmushroom cultivation are from two toten microns in diameter. (A micron isone millionth of a meter, while a typicalspore is about one ten-thousandth of aninch.)

When deciding which filter to use, youshould know what quantity of dust andspores a filter can trap, in addition toknowing that it can exclude flies.Testing is not an easy task on commer-cial farms. Instead, ask the supplier toprovide test data concerning particle sizeremoval using a standard ASRAE(American Society of Heating, Refriger-ating, and Air-conditioning Engineers)test. These are standard tests of whichthe most common is the “weightarrestance test,” that uses standard testdust and will show the percent effi-ciency of the filter media at removingparticles by weight. Typical fibrousfilters have efficiencies of 60 to 80percent, with some reaching 90 percentof the test dust trapped. HEPA filtersare the most effective at removing smallparticles and commonly have efficien-cies greater than 99.97 percent. This isthe percent of the total weight of thedust that is trapped and does not relateto a specific particle size. A filter with arating above 60 percent efficiencyusually will remove all particles of lessthan five microns.

The higher the efficiency of the mate-rial, the better the dust exclusion, buthigh-efficiency filters will cause more airrestriction than low-efficiency models.In general, higher-efficiency filters will

need more filter surface area to allowthe fan or blower to deliver sufficientair. Typically, the pressure drop for thefilter should not exceed 1.0 inch ofwater. Filters must be tested at themushroom house to ensure they do notrestrict the air too much. Also, the filtermust be able to withstand the rigors ofmushroom house installation. Paperfilters are very efficient but cannot beused in the moist atmosphere of amushroom house. Therefore, filtersmade from glass fiber or other syntheticmaterials are preferred. Some manufac-turers also coat filters with a viscousmaterial known as a tackifier to aid intrapping particles.

Once a suitable material is found andattached to a door, filter frame, or otheropening, the edges must be sealed.Gapped, loose, or bunched edges offilters or netting are excellententranceways for flies, and the filter isrendered useless if a good seal is notmade there. Flies are tenacious in theirattempts to enter a mushroom house,and they have nothing to do all day butlook for ways to get inside. They cansmell compost and will mill about theoutside until they find a way inside.Insects will follow the path of leastresistance; a fly walking along a wall willnot climb around or over the seam, butwill go under it if there is an openingbetween the material and the wall. Thesimplest method to seal the edges is tofold over the material and staple theedge directly to the doorjamb. Replace-able boards attached to the doorjamb asa stapling surface will extend the life ofthe jambs. Narrow slots into which thematerial is pushed or even Velcro cancreate effective seals. Regardless of themethod selected, a good seal is para-mount. Workers performing theinstallation must be trained to makesure the material is sealed and notsimply installed.

24

Additionally, an adhesive like TangleTrap improves the edge seal. Flies snaredby the adhesive not only are incapableof crawling under a filter but also areprevented from finding other cracks.This is more important than it mayseem, since you probably never willsucceed in sealing all of the cracks in abuilding. Spray adhesive on netting andfilter seams, doorframes, fan openings,and filter frames.

There are times when an entrancewaymust be opened for a very good reasonearly in the crop cycle, for exampleduring the three days before and afterspawning. Unfortunately, this is themost critical time for fly control in thecrop cycle. Fresh Phase II compost isvery attractive to the female sciarid fly,and the compost is very susceptible togreen mold colonization at this time aswell. (This will be discussed thoroughlyin later sections.) But this is also thetime when spawn and supplements,spawning equipment, and other itemsmust be brought into or taken from therooms. Often, a portable air conditionermust be installed in one of the doors tohelp cool the room. When performingthese tasks, limit the time the door isopen and take precautions to preventinfestation or contamination.

When employees bring equipment ormaterials into the growing rooms, theymust keep doors closed when notactually entering or exiting the room.Train them and remind them con-stantly. Teach your employees theimportance of keeping doors closed. Onthe other hand, an automatic doorcloser, even something as crude as aspring, rubber strap, or counterbalance,will help significantly to prevent flyentry if open doors are a problem onyour farm. Also, train employees torecognize and eliminate straight flyways.If a breezeway door is open, all roomdoors should be closed. For example,

when spawn is transported to a room, itfirst should be unloaded into thebreezeway via the entrance door whileall room doors are closed. Once all theboxes are inside the breezeway, close theoutside door and open one room doorto put the spawn into the room itself.While the door to the outside is open,direct fans at the doorway to helpprevent dust from drifting inside and tobreak up the flight paths of any fliesthat may try to pass through.

Portable air conditioners required at thistime usually are installed in an outsidedoor presenting additional exclusionchallenges. Until installation and sealingare complete, flies, spores, and dust havea direct and unimpeded path into thegrowing room. Installation, therefore,must be quick. The unit should be onwheels, and methods should be devisedto get it installed and sealed quickly.Attach a sheet of plywood with a borderof foam rubber to the front of theportable unit so it can be wheeledagainst the wall and sealed at the same

time. No tools should be requiredduring installation. Simple, hand-tightened turnbuckles can draw thefoam tight against the wall and jamb.Pay close attention to mated surfacesafter installation. Improper installationprovides entry points for flies. Lastly,spray the edges with fly trappingmaterial.

Though not as susceptible to diseaseorganisms as cooldown and spawning,the casing operation and casing prepara-tion can have pest problems. Phoridflies are attracted to actively growingmycelia, and Verticillium spores caninfest the casing. Take the same precau-tions during these operations as you useduring spawning.

Exclusion also involves controlling themovement of people and equipment.Anyone who has been in older rooms—harvesters, maintenance people,supervisors—must not be allowed toenter new rooms they could infest bybringing in contaminated casing or

Figure 12. Movement of employees between “clean” and “dirty” areas must becontrolled.

25

compost, spores, flies, or mites (Figure12). Harvesters should have lunch andbreak areas separate from employeeswho work in clean areas. Always assumethat areas are contaminated if fre-quented by harvesters or peopleworking in other dirty operations suchas Phase I compost filling. These areasmust be sanitized periodically, and ofcourse are always off-limits to peoplewho work in clean areas.

Equipment used in older rooms—hoses,spraying equipment, harvesting equip-ment—should not be used in cleanrooms. Make separate clean and dirtyroom equipment available. If a piece ofequipment must be used in both cleanand dirty rooms, sanitize it thoroughlybefore using it in a clean area. Forexample, always use spraying equipmentfor pesticide applications in clean roomsfirst and then in progressively olderrooms. Of course, the equipment mustbe sanitized before use in clean roomsthe next day.

Exclusion continues to be importanttoward the end of the crop. At thisstage, instead of trying to keep pestsout, they must be kept inside thegrowing rooms. Exclusion now is moreaptly called containment. Flies areactively seeking ways out of the growingrooms, looking for fresh compost orgrowing mycelium, and are most likelycarrying pathogenic organisms. Thoughnot as critical as the employees in thespawning operation, harvesters alsomust be trained to keep doors closed.Filters must be kept intact. Filterexhaust air as well, to prevent expulsionof spores and flies into the outside air.

26

References

Lomax, K. M. 1998. Air filter selection.Mushroom News 46:14–16.

Mushrooms are saprophytes, part of agroup of decaying organisms that arenature’s “janitors.” Together with otherdecaying organisms (various bacteria,molds, etc.), mushrooms (fungi)eliminate dead material in nature. If notfor the action of these “janitors,” theworld would be buried in dead plantand animal material.

In nature, it might not matter whichorganisms consume dead leaves or afallen tree, but in trying to grow aspecific fungi, the environment must bemanipulated. This is possible withspecific cultural control techniques.Proper use of cultural controls canmanipulate growing environments tofavor the cultivated mushrooms and todiscourage competitor organisms orpathogens. Mushroom mycelium canovercome a weed mold, for example, ifthe weed mold is put at a disadvantage.No other means of control are needed ifenvironmental manipulation is success-ful or the competing organisms areweakened to the point that they becomesusceptible to other controls such aspesticides or biological agents.

Many common IPM practices are notnormally thought of as cultural controls.Phase I and II composting, for instance,are good examples of cultural controls.Mushroom mycelium will grow readilyon many of the materials used to makecompost if those materials are auto-claved (sterilized in a sealed container)

and mushroom mycelium is asepticallytransferred into them. Composting isrequired to make the material pliable soit will hold sufficient water to sustainthe mushrooms through the crop and tocreate enough density to allow trays orbeds to be filled with the desired dryweight at a reasonable depth. However,the most important reason forcomposting is to make the materialsselective for mushroom mycelium(Figure 13).

If mushroom mycelium is added touncomposted materials—materials thatare not selective for it—competitororganisms will quickly take over. Theyare able to grow much more quicklythan mushroom mycelium and willexclude the mushrooms through rapidgrowth, heat production, or productionof antibiotics (chemicals that preventthe growth of other microorganismssuch as fungi and bacteria). Mostmicroorganisms produce antibiotics as aform of chemical warfare to controltheir territories. (Penicillin is a goodexample of an antibiotic produced by afungus, in this instance by Penicilliummold.) Composting changes the rawmaterials, making them more attractiveto the mushroom mycelium andallowing the mushroom to outcompetethe competitors. Composting, therefore,is a form of pest control, and as such ispart of any good IPM program.

A. Specific Control Techniques

2. Cultural Control

Phillip S. Coles

William Barber

27

In nature, a succession of organismswork together to decompose organicmatter, and a similar process takes placewhen compost is made and mushroomsare grown. Mushrooms are simply oneof the organisms in the succession,though it is imperative that mushroomsare introduced at the right time in thesequence. When raw materials come tothe compost wharf, they should be dryto prevent microbial action and decay.Once they are wetted, the compostingprocess begins. The first organisms togrow are the opportunists, fast-growingmicrobes that release a lot of energy,CO

2, and water. This causes the

compost to become hot and explainswhy it requires abundant oxygen. Ifcomposting is done correctly, microbeswill produce ammonia and concentratesimple carbohydrates into larger

molecules. The more complex carbohy-drates are saved for a later time whenthe mushroom mycelium is introduced,because unlike many of its competitors,mushroom mycelium is capable ofproducing enzymes that can break downthese larger molecules. The presence ofthese large molecules, after a properlymanaged Phase I, is one of the charac-teristics that makes compost selectivefor mushroom mycelium. Anothercharacteristic is the conversion ofammonia, by the action of compostmicroflora, to microbial protein. Thisstage is Phase II composting.

It is not enough simply to allowcomposting to proceed uncontrolled. Ifcomposting materials are too dense ortoo wet, air will be excluded andanaerobic organisms will begin to grow.

These organisms will ensile the com-post. This is desirable in a silo wherematerials are placed with the intentionof excluding oxygen and growingorganisms that will ensile the materialso it will “keep” and can be fed to cattleat a later date. However, this is com-pletely undesirable when producingmushroom compost. Anaerobic organ-isms in mushroom compost make thecompost selective for other types oforganisms by “keeping” the nutrients inthe wrong form and by producinganaerobic compounds that are difficultto break down during the compostingcycle. Regardless of when they areproduced in the composting process,anaerobic compounds are toxic tomushroom mycelium if they remainafter Phase II.

Figure 13. Making selective compost is one of the most important components of cultural controls and IPM.

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Temperature is a good indication ofwhat is occurring inside the compostpile (Figures 14A and 14B). Hightemperatures indicate that aerobiccomposting is taking place. Lowtemperatures, on the other hand, can bean indication of anaerobic composting.

Compost formulation is an importantpart of IPM. If the formulation isincorrect, excess nutrients will be left inthe compost. If nitrogen supplementa-tion is too high, for instance, excessammonia will be produced. Ammoniaabove .05 percent is toxic to mushroommycelium and promotes the growth ofundesirable fungi like Coprinus. (SectionII.C.3.) Conversely, supplementcompost with too little nitrogen andsimple carbohydrates will remain(residual) in the compost after Phase II.Excess carbohydrates promote thegrowth of fast-growing competitororganisms like Aspergillus, which willovertake mushroom mycelium.

Length of composting in either extremecan have results similar to under- andover-supplementation. If Phase I is tooshort, excess carbohydrates will remain.If it is too long, energy will be depleteduntil not enough remains in thecompost for conversions required inPhase II.

Figure 14B. The effect of temperature ongrowth rate.

Gro

wth

Rat

e

TemperatureMinimum Maximum

Optimum

Figure 14A. Relation of temperature to growth rates of a typical psychrophile, a typical mesophile, a typical thermophile,and two different hyperthermophiles. The temperature optima of the example organisms are shown on the graph.

Gro

wth

Rat

e

0 10 20 30 40 50 60 70 80 90 100 110Temperature (oC)

4o

39o 600

88o 106o

PsychrophileExample:Polaromonas vacuolata

MesophileExample:Escherichia coil

ThermophileExample:Bacilusstearothermophilus

HyperthermophileExample:Thermococus celer

PsychrophileExample:Pyrolobus fumaril

60o

Phase II

In Phase II, an entirely different set oforganisms grow. These organismsconsume ammonia and convert it toprotein. Ammonia contains a nitrogenmolecule that is essential to proteinformation, and the Phase II organismsare capable of obtaining this moleculefrom ammonia. Later, these organismswill become the protein source formushroom mycelium. They also use theremaining simple carbohydrates leftover from Phase I as fuel. The impor-tance of the Phase I formulation shouldbe apparent.

Just as Phase I can fail due to manage-ment practices, incorrect temperaturemanagement in Phase II can spelldisaster for pest control. If the tempera-tures are too low or too high, ammonia-converting microbes will be unable toperform effectively. If temperatures inthe compost are too high, for instance,Phase I conditions will recommence andammonia production will continue.Furthermore, the organisms that thriveat high temperatures and produceammonia will use some of the simplecarbohydrates the Phase II ammonia-converting organisms will need. Therewill not be enough simple carbohydrates(energy) for these organisms to convertthe ammonia. They literally will run outof food, and the unconverted ammoniawill cause problems for the mushrooms.If temperatures are maintained at levelsthat are too low, ammonia-convertingmicrobes will not survive, since theyrequire specific temperature ranges toflourish.

Pasteurization

Pasteurization is another critical pestcontrol step in Phase II. Compost cancontain many types of pathogenicorganisms. Nematodes are the mostcommon, but other types of molds andtheir spores also are present. Properpasteurization ensures their destruction.Compost pasteurization serves the samepurpose as the pasteurization of milk.Temperatures are raised sufficiently andfor an adequate time to ensure thedestruction of pathogens, but are lowenough to allow the survival of benefi-cial microflora. By pasteurizing ratherthan sterilizing, which is done attemperatures that will destroy allorganisms, surviving beneficial microf-lora help to exclude pathogens that latermay be introduced to the growingroom. The microflora exclude patho-genic organisms by “tying up” sites, orprohibiting pathogens from obtainingsubstances they require, such as food.They also are capable of producingantibiotics, which can destroy patho-genic organisms. The microflorapopulation remaining after pasteuriza-tion is important, therefore, to thesuccessful completion of Phase IIcomposting, but also serves as directcompetition for invading pathogens.

Temperature and HumidityControl

During spawn run, optimal temperatureis again very important. If the composttemperature is too low, mushroommycelium, obviously, will grow slowly.Although growth of pathogenic organ-isms also will be slowed, their growthwill not be retarded as much as that ofmushroom mycelium. High tempera-tures are a greater problem. They notonly will weaken or kill mushroommycelium, depending on the tempera-ture ultimately reached, but also willpromote the growth of heat-producingcompetitors. These make temperaturecontrol more difficult. To make mattersworse, dead mushroom myceliumbecomes a source of simple sugars,providing food for the competitororganisms.

It is not adequate to rely on a good“average” temperature. The average of110°F (43°C) and 40°F (4°C) is 75°F(24°C), but neither temperature isconducive to optimal spawn growth.Hot areas must be located and con-trolled before they spread and causesevere localized damage similar to thedamage occurring in an entire roomthat has overheated.

After casing, while temperature remainsimportant for reasons similar to spawnrun, there are additional considerationsas the crop progresses. If temperaturesare raised to promote early maturationof mushrooms, other organisms such asVerticillium can increase their popula-tions very rapidly. Although the elevatedtemperatures may cause the mushroomsto mature more rapidly, Verticillium willspread even faster.

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Relative humidity control, as mostgrowers realize, is important for overallmushroom quality, but it is also animportant part of IPM. A film of wateron wet mushrooms provides an idealhabitat for Psuedomonas tolassi, thecausal agent of mushroom blotch.Maintaining dry mushroom surfaces isthe most effective method for prevent-ing blotch, and relative humiditycontrol is one tool for accomplishingthis. (See Bacterial Diseases, ChapterII.C.4.)

Shortening Crop Cycles

Any technique that shortens the lengthof the crop cycle aids pest control byreducing the amount of time pathogenicorganisms have to reproduce. Thestrategy is to complete the harvest andpasteurize the room before pest popula-tions can damage the crop. The benefitsare twofold: first, when pest organismsenter a growing room, they do not havesufficient time to reach economicallyinjurious levels within that crop.Second, it reduces the amount ofinnoculum on the farm for new crops inother rooms. This applies to arthropodpests as well as fungal pathogens.

There are many ways to reduce the timeneeded for the cropping cycle. Mostimportant, run the growing roomsproperly from the start. Low tempera-tures or mechanical problems inspawning or casing can delay the onsetof picking and expose the room toexcessive increases in pest populations.Phase II rooms must be brought intoconditioning range without undo delay.Cooldown-to-spawning times should bekept to a minimum, and properspawning rates must be used to ensurecomplete colonization in a minimalamount of time. During cropping,remaining mushrooms from each breakshould be stripped to help the nextbreak come in more quickly.

Growing techniques that shorten cropcycles also should be considered, such asadding CAC-ing (Compost At Casing)to the casing layer and reducing thenumber of breaks. Through-spawningand supplementation are examples ofmethods used in the past to shortencrop cycles.

Sanitation

Sanitation is essential for controllingmushroom diseases and arthropod pests,because it will slow the spread ofpathogenic organisms as well as lowertheir overall populations in the mush-room-growing environment. The placeto start is outside the growing rooms.Roads and the immediate vicinity ofmushroom houses should be paved withconcrete or macadam, since dust is anexcellent carrier for the sticky spores ofVerticillium or Trichoderma. Areasaround growing rooms, tunnels, andother sensitive locations should be keptfree of dirt. In dry weather, water tokeep dust to a minimum. These areas,also, should be kept free of clutter.Debris provides hiding places for flies,sheltering them from inclementweather. Mow grass to reduce areaswhere flies can hide from sun, frost, orrain.

The walls and floors of rooms must bewashed and sprayed with sanitizers toensure all pathogens are destroyed.Steam pasteurization within a room isnot sufficient to ensure these surfacesare free of pathogens, since the wallsand floors act as heat sinks. Heat isconducted through the floor into theground, which has an almost infinitecapacity to absorb heat, maintaining thefloor cooler than the room air in contactwith it and ensuring such surfaces willnever attain pasteurization tempera-tures. For the same reason, the basementfloor of a house always will be coldunless it is insulated.

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The importance of washing beforesanitizing cannot be overemphasized,because any dirt left on a surface quicklyties up a sanitizer. This renders itineffective and essentially protects anyspores or other potential pathogensfrom being destroyed.

Hallways can harbor carry-overs fromprevious crops. All hallway surfacesmust be washed and sprayed. Any areasthat cannot be sprayed, such as electricpanels, must be wiped down with acleaner and disinfectant.

Once growing rooms are clean, theymust be maintained that way. Thiswould be easy if they could be sealed,but people and equipment must enterrooms to perform mechanical opera-tions and monitor the crops. Themovement of equipment and people ona farm must be controlled. Equipment,for example, should be separated andcolor-coded according to department oruse to ensure that dirty equipment suchas squeegees from filling operations can’tbe used in clean areas.

Within the room, good housekeepingminimizes the multiplication of pestorganisms. Keep growing surfaces freeof organic matter such as dead mush-rooms, which can serve as food sourcesfor pest organisms. Mushrooms shouldbe picked tight to reduce the chance ofspreading spores containing virusparticles.

Steam-off is an important part ofmaintaining low pest populations.During cropping, pest organismpopulations will increase inside thehouse and are potential sources ofcontamination for new growing rooms.Steam-off, or post-crop pasteurization,eliminates these contamination sources.Prior to steaming, growing roomsshould be closed, and openings such asthose for fans should be closed toprevent the escape of pathogens as the

room is heating up. If fly populationsare very high, the room should besprayed with quick knockdowninsecticides to prevent escape once thesteam is turned on. After steam-off hasstarted, monitor both compost and airtemperatures with probes. Raise the airtemperature with live steam to 160°F(71°C) and maintain it there until thecompost reaches the same temperature.Begin counting time when thecompost reaches 160°F (71°C). Thecompost temperature should be 160°F(71°C) for at least 5 hours to ensure anadequate kill of all pathogens. Ifpathogenic organisms are found to besurviving steam-off, wet the casingsurface before injecting steam to helpwith heat transfer through the compostand casing. Also, more time can beadded to the steam-off.

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Introduction

Biological control provides the mush-room grower with natural tools tocontrol mushroom pests. Natural anti-pest capabilities of nematodes, wasps, orbacteria are exploited. Biological controlalso capitalizes on the properties ofchemical substances released by the pestor by food on which it is feeding.

Biological control methods offer manyadvantages over chemical control: theagents have a specific host range, thereare no toxic residues, and concern forworker exposure is reduced. Biologicalcontrol methods can target a pest andreduce its numbers to an acceptablefarm operational level. In addition, thecontrol agent may be self-perpetuating,reducing the need for frequent reappli-cations. Development of resistance israre.

Biocontrol requires the support of anIPM program to create the conditionsunder which biological agents can bemost effective. For example, the agentmay act only against an immature stageof the pest and have little impact on theadult, necessitating that the IPMprogram call for its use when theimmature forms are predominant in thepest population. Or the biocontrolagent may be more susceptible than thepest to pesticides and may be killed orweakened when pesticides are used as

A. Specific Control Techniques

3. BiologicalControl

Danny Lee Rinker

part of existing pest control practices.The IPM program would be alert to thispossibility. Application of the biocontrolagent would be withheld until chemicalresidues have dissipated, or a controlagent may reproduce more slowly thanthe pests and never “catch up” once thepest population is high. An IPMprogram then may include other means,perhaps chemical controls, to lower thepest numbers. The biological system canbe left to do what it does best—maintain low pest populations.

An IPM program can help the farmermanage other limitations of the biologi-cal control method—longer time topeak effectiveness, incomplete elimina-tion of the pest, cost, and inability toovercome the overwhelming pestpressures resulting from poor house-keeping—by calling for other controlmeasures when they in turn are mosteffective. And, because biological agentsmay have detrimental effects on themushroom crop if applied improperlyor when their use is not warranted, anIPM program must be in place toensure that the biological agent servesthe grower’s needs while avoidingreductions in crop yields or quality.When supported by an IPM program,biological control methods can expandthe mushroom farmer’s arsenal of pestcontrol weapons.

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Biological control programs in themushroom industry are currently beingused for nuisance flies on compostwharves, sciarid flies, and blotch disease.Additional potential agents for biologi-cal pest management in the mushroomindustry are cited.

Nuisance Flies on CompostWharves

The house fly (Musca domestica) and thestable fly (Stomoxys calcitrans) arecommon to compost wharves. Aneffective biocontrol method augmentsthe number of naturally occurringPteromalid wasps. These tiny wasps areparasites that attack the immature pupalstage in the fly’s life cycle. The wasps arenocturnal and do not sting. Commonlyused species are the Spalangia endius,Muscidifurax raptor, M. zaraptor, and M.raptorellus.

The Pteromalid wasp has a life cyclesimilar to other insects: egg, larva, pupa,and adult. Most of this wasp’s life cycleoccurs within a host that providesnutrition and protection for all stagesother than the free-living adult wasp.House flies and stable flies are amongtheir potential hosts. The adult wasplays her eggs into the nuisance fly’spupa. The immature parasites consumethe host’s tissues from the inside, andadult wasps “host feed” on fluids fromthe outside, preventing the fly fromdeveloping into a healthy adult. Thewasp’s life cycle requires two to fourweeks. Under optimal conditions, theparasites can reduce the nuisance flypopulation in 4 to 6 weeks. Completeelimination of flies usually is notpossible, especially where there ismigration onto the farm from off-sitelocations.

Parasitic wasps must be integratedwithin a pest management program.Reducing conditions favorable tobreeding helps to limit fly populations.Flies will reproduce in moist organicmatter; therefore, promote gooddrainage, remove seepage, and minimizestanding water to lower the number ofnuisance flies. Good sanitation on thewharf, rotation of raw materials, andremoval of spent substrates from thefarm also will expedite fly management.Routine fly monitoring is essential toevaluate the necessity and effectivenessof a management program. Release ratesof parasites are dependent on flynumbers, environmental and climaticconditions, migration from off-sitelocations, and chemical controls.

Wasp release early in the season is agood strategy, since the fly pests havecertain survival advantages over thewasps—greater reproductive capacity,ability to fly greater distances, andgreater resistance to pesticides. If thenumber of adult flies is too high, baittrapping can initially reduce it. Oncethe adult fly number is lowered, thewasps can be used to keep the pestsunder control.

Sciarid, Phorid, and CecidManagement

Mushroom fly pests are a consistentproblem for growers. The three flygroups most commonly encountered arethe sciarid fly (Lycoriella mali), thephorid fly (Megaselia halterata), and thececid fly (Mycophila speyeri, Heteropezapygmaea). The sciarid larvae attackcompost, spawn, mycelia, pins, andmushroom stems and caps. The larvaeof phorid flies feed on mycelia, causingdepressed crop yields. Cecid larvae feedon the mushroom stems or gills,reducing marketable yield. Sciarid andphorid adults carry disease organismsinto the crop. Mushroom flies arediscussed in greater detail in ChapterII.C.1 of this manual.

Nematodes as Control AgentsAgainst Mushroom Flies

Mushroom flies are good targets forbiocontrol with beneficial nematodes.More information on nematodes,especially those that negatively affect themushroom crops, can be found inChapter II.C.5 of this manual. Benefi-cial nematodes, those that can play arole in biological control, are coveredhere.

Howardula husseyi as a ControlAgent Against PhoridsHowardula husseyi is an endoparasiticnematode that occurs naturally in thephorid population. This nematode livesboth in the compost and in the fly. Ithas a six- or seven-stage life cycle: egg,four or five immature larval stages, andadult. Some of these immature-stagelarvae are free-living, while others areparasitic. Both adult male and femalephorids are commonly infected withnematodes.

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When the female phorid attempts to layeggs on spawned mushroom compost,she also deposits second-stage nematodelarvae. Female and male nematodelarvae develop and mate while in thecompost. The fertilized fourth-stagefemales (“infectives”) enter the phoridlarvae or young pupae and develop intoadults while in the phorid body cavity.While inside, they also deplete anddisorganize the fly’s food reserves andlay eggs. After the eggs hatch, the youngnematodes work their way through thephorid ovaries into the oviducts. Whenthe female phorid attempts to oviposit,she discharges the nematodes.

While in the phorid, the growing anddeveloping nematodes reduce thephorid egg production by 50 to 100percent. Under controlled lab condi-tions with parasitism increasing uncon-trolled, phorid populations can bevirtually eliminated within five flygenerations. Commercialization of thisnematode species has not been success-fully achieved.

Steinernema feltiae as a ControlAgent Against SciaridsA beneficial entomopathogenic nema-tode, Steinernema feltiae, has beenimpressed into service as a biocontrolagent against sciarids. This nematodespecies carries bacteria that are deadly tothe sciarid fly. Bacteria live within thegut of the nematode and are releasedonce inside the host. The nematode lifecycle includes the egg, four juvenilestages, and the adult. The third juvenilestage generally enters the third or fourthlarval stage of its host through naturalbody openings like the mouth, anus, orspiracles, or it may go directly throughthe body wall. Once inside the host, thenematode makes its way into the bodycavity of the insect larva and releases thebacteria. These bacteria rapidly kill thehost within 48 hours by blood poison-ing. The immature nematodes feed on

the new bacterial cells and host tissuesand then develop into adults. The adultnematodes reproduce in the host. Youngnematodes, finding the food supplydepleted, will exit the cadaver.

Infective-stage nematodes can beapplied to the casing material at casingor later during the crop. The nematodesdo not feed in the compost or casing.They can be responsible for high levelsof mortality among L. mali larvae. Labtrials have shown S. feltiae to causemortality levels up to 100 percent. On-farm trials have attributed lower, butsignificant, reductions in fly emergence(e.g., 66 percent fly emergence) to thepathogenic effects of S. feltiae whenapplied at rates of 81 million nematodesper 100 m2. In order to achieve highermortality, current supplier recommen-dations are 300 million per 100 m2.

Microorganisms as BiologicalControl Agents of MushroomFlies

Bacillus thuringiensis subspeciesisraelensis (Bti) is a bacterium that isused widely in biocontrol. The bacte-rium produces both a protein crystaland a spore. Once eaten by the larva,the crystal degrades in the alkaline gutof the insect. The insect’s gut subse-quently becomes paralyzed, and larvaldeath occurs within 48 hours.

Field trials have demonstrated control ofphorids and sciarids when Bti wasapplied either to compost or casing.Small-scale research trials with oneformulation have demonstrated that acompost application could provide 85percent sciarid control. An applicationto casing at a lower formulation ratemanifested a 70 percent control level ofsciarid larvae. Excessive mycelial growthon the casing or reductions in yieldsmay occur from a casing application.Bti appears to be more effective againstyounger rather than older sciarid larvae.

Mites as Control Agents againstMushroom Flies

A predator consumes its prey, eitherpartially or entirely. One such predatorin the mushroom crop is the miteHypoaspis miles. This mite will preyupon larvae of cecids, phorids, andsciarids. These mites are commerciallyavailable for use in the greenhouseindustry, but none are being used at thistime in the commercial mushroomindustry. The mite is less than 1 mm insize and light brown in color. The lifecycle is complete in about two weeks. Insmall-scale experimental trials, sciaridswere controlled at 96 percent using 750mites per m2. However, field trials inOntario were not as dramatic, with lessthan 30 percent control of sciarids. Themites do not suppress mushroom yield,nor are they found on mushrooms.Mites have several advantages. They aremobile and can easily search for prey;mushroom growing conditions aresuitable for their reproduction; and theycan live for several weeks without food.Despite the low control rate thus far,predatory mites do have potential forsuccessful integration into biocontrol ofmushroom pests.

Fungi

Some fungi are capable of invading thebodies of flies. The pathogen spore ormycelium penetrates, develops, and killsthe host. After death of the host, sporesare produced on the cadaver’s surface.These spores then will infect others. Thedevelopment of Pandora gloeospora hasshown promise for control of sciarids.

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Biologically DerivedChemicals Used inBiological Control ofInsects

The term “biological control” has cometo include the use of chemical sub-stances with control potential. In somecases, insects themselves may be thesource of the chemicals that will attractothers. Or, substances can be producedby the food source that may eitherattract or repel insects.

Pheromones

Pheromones are volatile chemicals thathelp insects find each other or causesome other biologically importantresponse. The compounds are speciesspecific and are detected by the insect inminute concentrations. In a biologicalcontrol program, these chemicals areused to attract large numbers of thepests (mass trapping) to stop aninfestation or, conversely, to confuse thepests so the two sexes cannot find eachother to mate. Sex pheromones havebeen demonstrated for phorids andsciarids. However, commercial trialsusing synthetic compounds have notbeen successful.

Kairomones

Kairomones are volatile chemicalsproduced by a pest’s food source thatalert the pest to its presence. They couldbe used as a chemical message to lurepests into traps. The attractiveness ofcompost to sciarids during Phase IIcool-down or of actively growingmycelia to phorids are observed events.However, researchers have not been ableto duplicate the phenomenon observedin the field.

Repellants and Anti-Feedants

These chemicals act as a “self-defense”mechanism for the food source. Theyeither repel the pest from the foodsource before it feeds (repellant) orafterwards (anti-feedant). Calciumoxalate, a byproduct of mushroommycelial metabolisms, has been foundto have repellant activity toward thelarvae of sciarids. By itself, calciumoxalate is not an effective controlmethod, but as part of a wider program,it may prove to be useful.

Disease Management

Most biocontrol efforts againstmushroom diseases have focused onbacterial blotch. Bacterial blotchdisease, caused by Pseudomonas tolaasiior P. gingeri, has been managedcommercially by another bacterium (P.fluorescens biovar V). The biocontrolagent acts as a preventative, becomingestablished before the development ofa blotch population. It competitivelyexcludes the colonization and develop-ment of the blotch population.Bacteriaphages (viruses that infectspecific bacteria, usually killing them)also have been used successfullyagainst blotch. Combining bothorganisms could be highly effective.

Conclusion

Biological control of mushroom pests isa reality. Parasitic nematodes and waspsare commercially available and arebecoming integrated into pest manage-ment programs, while other organismsincluding fungi, bacteria, and mites arebeing developed. The prospects arefavorable for the development ofeffective biological control agents in thenext several years.

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Integrated Pest Management is notsynonymous with organic or pesticide-free production, as many people believe.Judicious use of chemical pesticides isan integral part of an IPM program. InIPM, pesticides are not applied on arigid schedule as they are in a chemi-cally dependent pest control program.They are one facet of a broad (inte-grated) approach to pest management,though one that frequently can beminimized or avoided altogether.

Many pesticides appear to providesuperb pest control independent ofother control measures. After anapplication of a contact material, forinstance, many dead insects may litterthe outside of a plant, temptingcomplete reliance on such products.After a simple (though not inexpensive)application, the grower feels good. Theapplication complete, there is now moretime to devote to the long list of otherduties that confronts a grower each dayon a mushroom farm. Regularlyscheduled pesticide applications,therefore, become appealing.

But using chemical pesticides in thisfashion is destined to develop pestresistance to them. Pest organismsreadily become resistant to overusedchemicals. (See Chapter II.B, Resistancemanagement.) Pesticides in an IPMprogram, however, are applied as a lastresort and are used in accordance withmonitoring, established economic

thresholds and temperatures, and neveron a rigid schedule. Also, pesticides aremost efficient if used when they canlower a high pest population rapidlyand significantly, providing the growerthe opportunity to get the pest undercontrol and possibly saving a cropobviously in peril. Other IPM strategiesthen can maintain that level of control.

There are two pesticide applicationtechniques on a mushroom farm. One ispreventative, and is predicated onmonitoring and temperatures, whilemonitoring exclusively triggers theother. Preventative applications servethe same role as physical exclusion.Instead of making it physically impos-sible for fly entry, however, a chemicalbarrier is applied in an attempt to killthe fly before it gains access to thegrowing room. This is not as effective asphysical exclusion, but it is a backup toit if some entry points have beenoverlooked. Use a contact poison forthis application. There are other types ofpesticides, but more on them later.

Preventative applications do not replacediligently sealing the growing room. Onthe contrary, the two must worktogether. (See Chapter II.A.1, Exclu-sion.) If a contact spray were usedwithout physical exclusion, only themost resistant flies would be enteringthe rooms to reproduce. In effect, youwould be screening for “super flies.”

A. Specific Control Techniques

4. Chemical Control

Phillip S. Coles

37

Only use spray when weather is condu-cive for fly movement and whensignificant fly populations exist on thefarm. Every farm will be different, andeach farm should develop its ownprocedures dictating when sprayingshould take place. If the temperature isbelow freezing outside and yourgrowing rooms are physically separated,flies cannot move from old to newrooms or from the wild population intonew rooms. Determine at what tem-peratures they will move on your farm,and do not use preventative sprays whenthe outside temperature is below theestablished figure. (See Chapter II.C.1,Arthropod Pests, for flight tempera-tures.) You may want to decrease yourthreshold by a few degrees to add asafety margin.

Assess fly populations in two ways.First, population numbers should beavailable from monitoring inside thegrowing room. Have the numbers beenhigh, or are they becoming high?Managers at each farm must decide justwhat is “high” when referencingmonitoring data. Second, growersshould have a good feel for fly popula-tions from time spent in the growingrooms. In early crop stages, usually it isnot possible to detect flies withoutmonitoring. If you can, you have a veryserious problem! But, in the later stagesof harvesting, high fly populations aredetected easily. A grower must makespraying decisions with this informa-tion. An example of a spray-triggeringscenario might be a daytime hightemperature above 50° F (10° C),obvious fly populations in old harvest-ing rooms, and spawn run fly countsconsistently above 10 flies per day.Obviously, the parameters would varyfrom farm to farm.

A common use for preventative sprays isapplications to the outsides of buildings.Outside spraying, however, has seriousdisadvantages. It is difficult to getcomplete coverage around and on top ofa building. It cannot be done duringinclement weather. The pesticide isexposed to the elements—rain can washit off—and ultraviolet rays from the sunbreak it down. There are also environ-mental concerns. The pesticide isoutside where it can contact non-targetorganisms, and care must be taken notto contaminate streams or other water

supplies. Never spray when there is achance of drift.

Chemical applications to enclosed areasoutside of the actual growing area, suchas hallways and lofts, are a moreeffective use of preventative sprays thanon the outer surfaces of buildings. Goodcoverage is attained more easily; thematerial is protected from degradationand wash-off; non-target organismexposure is limited; and the percentageof pest populations exposed to thepesticide also is limited. This helps with

Figure 15. Fly light with many sciarid flies on it.

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resistance management, since targetorganisms must penetrate the walls ofthe growing building before coming incontact with the pesticide. Logicaltargets for pesticide applications areinside growing rooms, on beds or trays,and on any plastic covering the com-post. Of course, pesticides used ingrowing rooms must be labeled formushroom use.

Despite exclusion and the use ofpreventative pesticidal applications,some flies still can gain access to agrowing room. To know whether fliesare entering a room—and the magni-tude of the invasion—you mustmonitor. The Pennsylvania Fly Monitorprovides the best way for commercialfarms to monitor fly populations. Thismonitoring device is simply a blacklight fastened to a board with a strip ofsticky paper on either side of the light(Figure 15). The monitor should beplaced in a location proven to collectthe most flies of any area in the room.The location will vary from farm tofarm, necessitating some experimentingat the outset. Keep in mind that fliestend to be lazy and won’t travel farunless it is necessary. Therefore, the

monitor usually is placed above thehighest bed so the light can be seenfrom a large portion of the room, aswell as near areas of the room wherepenetration most likely occurs. Fliesshould be counted daily and thisinformation used to make pesticidedecisions. Decisions can be madeaccording to daily or cumulative counts.Daily counts would trigger the use of aknockdown material, an adulticide,while cumulative counts would dictatethe use of a larvicide in compost orcasting.

Remember, a fly monitor does not catchall of the flies in a room. It traps only apercentage of them. The monitor wasoriginally tried as a control method. Itwas hoped the flypaper would captureincoming flies, and that would be theend of them. After testing, only apercentage of the flies were caught, andthese almost exclusively were femalesthat already had laid their eggs. Thismeant the monitor was useless as acontrol technique; but by sampling thepopulation, it gave a relative fly countfor the room and therefore was valuablefor making pest control decisions.

It is important at this point to distin-guish between different types ofmaterials, for this will establish howthey are to be used. As stated earlier,contact poisons make very goodpreventative sprays. They are in place ifa fly tries to enter a growing room andare effective against adult flies. A quickknockdown material such as a pyre-throid fog is very useful if flies suddenlyappear on the monitor in cooldown orearly spawn run. Larvicides and growthregulators are good for mixing with thecompost and/or casing to prevent theflies from reaching adulthood andproducing another generation.

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Type of Material Uses When to Use

Contact poison, adulticide Preventative, exclusional spray. Prior to air in growing roomsreaching 100° F (38° C), or beforecooled compost is brought ina tray or tunnel system.

Quick knockdown, adulticide Good when large number of invaders When fly monitors indicateare present, or at the end of a crop when an influx of invading adultsyou want to prevent them from exiting a at the beginning of the crop,room and invading new rooms. or when the grower feels fly

populations in an old roomare high enough to threatennew crops. It also works wellas a knockdown to preventflies from escaping the roomas steam is being injected.

Growth regulator or similar larvacide To prevent eggs laid by When cumulative fly countsinvading adults from developing dictate their use.into adults, producing latergenerations.

Establishing EconomicInjury Levels

Pest control decisions must be based onmonitoring. Even preventative sprayshave a monitor count component.Unfortunately, there are no concrete,scientifically established economicthresholds for mushroom farms. Thesenumbers are somewhat arbitrary andmust be determined by the growers ateach farm. If extensive scientific studiesexisted, there still would be dramaticdifferences from farm to farm, andeconomic injury levels (EIL) wouldhave to be customized.

To develop individual EILs, the growermust consider the level of potentialdamage. For example, sciarid flies causemuch more extensive crop loss thanphorid flies, and can decrease quality byburrowing into the mushroom stems.Therefore, higher numbers of phoridsthan sciarids can be tolerated. There areadditional outside influences. If diseaselevels are low, a fairly high number offlies may be acceptable. But those samepopulations can be devastating if thereare high levels of Verticillium and/orgreen mold on a farm. The sciarids arevery important vectors of green mold,since they are most attracted to thecompost during cooldown, precisely thesame time green mold infections aremost likely to occur. When Verticilliumis high, only low populations of bothflies can be tolerated, keeping in mindthat the high activity level of phoridsmakes them better at spreading thedisease. All of these factors must betaken into account when trying todetermine the economic thresholdtriggering a pesticide’s use.

An example of an economic thresholdfor sciarid flies is two flies a day untilthe end of spawn run, then 10 per daythrough harvest. Obviously, higherpopulations can be tolerated as the cropprogresses (see Part I, Theory ofIntegrated Pest Management). This isalso an example of a daily EIL. If morethan two flies per day appear on the flymonitor, the grower would be justifiedin spraying a fogging adulticide to killthe incoming invaders from that day.

Cumulative counts determine the use oflarvicidal agents added to the compostand/or casing. High fly counts early inthe crop would indicate future prob-lems, since a significant number of theinvading adults probably will besuccessful in ovipositing in the compost.A strategy is needed to prevent themfrom producing subsequent generations.If a material is added to the casing layer,there is more than adequate time for thegrower to make a control decision. Forexample, if experience had shown thatsignificant fly damage would result ifmore than a cumulative total of 200sciarid flies (a cumulative EIL) hadentered a growing room prior to casing,then a larvicide should be added to thecasing. On the other hand, if a materialmust be added at spawning, there is notas much time to make a pest controldecision. In this instance, the materialhas to be applied before the spawningmachine mixes the spawn with thecompost, so the cumulative EIL wouldbe a specific number of flies on themonitor up to the day of spawning orpossibly until spawn broadcast. If alarvicide is added to the compost—either on the compost wharf or at fill—it is more similar to a preventative spraythan a spray based on an EIL; therefore,preventative spray criteria woulddetermine whether or not the larvicidewas used at this stage.

Formulations

There are several types of formulationsused for pesticides, each having its ownadvantages and disadvantages. Somepesticides are available in more than oneformulation, so their use can varydepending on the situation. Mostpesticides are available in only oneformulation, so their effectiveness mustbe weighed against the advantages of theformulation.

Classes of Pesticides

There are several classes of pesticides.Some, like the organophosphates andcarbamates, contain some of the originalpesticides such as DDT. The moremodern materials such as insect growthregulators (IGR) are becoming morecommon. They also are safer than theolder materials and much more specificin their range of effectiveness. Thegrower doesn’t have much choice inwhat class of pesticide is used, sinceonly those registered can be used. Workwith your sales representative to decidewhich ones are best for your applica-tion.

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Testing

Finally, no pesticide, regardless of howsafe or easy to use, is of any value if itdoes not kill the target pest or pathogen.Pesticides must be tested, and theyshould be tested against the specific fliesof a given farm. Just because tests showgood efficacy against sciarid flies for amaterial does not necessarily mean itwill be good against your farm’s sciaridflies. Genetic variation occurs betweenindividuals and between differentpopulations. Generally, when a materialis new it will work well, but as it is used(or misused) resistance develops, atdifferent rates in different populations.The only way to be confident in apesticide’s efficacy on your farm isthrough testing.

Some testing is easy to do and can bedone at the farm level, while other testsare too difficult and require a profes-sional. The expertise of the personnel ona given farm will dictate how much ifany of the testing can and should bedone there.

There are many simple ways to testpesticides. Fungicides are difficult totest because of the difficulties ofworking with the various pathogens.Generally, insecticides are relatively easyto test. The easiest are the quick-knockdown fogging materials. Make acage using fly netting that will preventthe flies from escaping, but that also willallow air movement. Place some fliesinto the cage and hang it inside a roomthat is scheduled for fogging. After theroom has been aired out, count thenumber of dead and surviving flies.

There are several ways to evaluatecontact materials. It can be as simple asplacing wood blocks in an area that isbeing sprayed. Remove the blocks, placethem in a container, and add flies to thecontainer. If the flies die, the materialworks. Also, a lid to a container can befastened to a wall or ceiling, or simplyplaced on the floor. After it has beensprayed, fill a container with flies andattach it to the lid to see how the fliesdo. This involves a little more risk, soavoid taking flies into the growingroom. Reserve this method for outsidesprays.

Remember that flies are relatively fragileand do not live long, whether they areexposed to pesticides or not. So youalways should have a control group forpurposes of comparison. If the unex-posed flies die, they may have beenmishandled. Try the test again.

Once everything is in place to performthe test, flies must be collected. They arevery small and fragile, and collectingthem is no easy task without the rightequipment. The best way to collect fliesis with an aspirator. Aspirators areavailable commercially, some withbattery-operated pumps. These areuseful if you are collecting largeamounts of flies on a regular basis, butyou also can fashion an inexpensiveaspirator from some very inexpensivelab materials that will suit the purposeat almost any mushroom farm. All thatis needed is a flask or bottle with arubber stopper that has two holes. Ineach hole is a short piece of glass tubingwith rubber tubing attached. One of thepieces of glass tubing will have a pieceof netting over the end inside the jar. Tocollect insects, suck on the end of thefiltered rubber/glass tube while holding

Formulation Advantages Disadvantages

Emulsifiable Concentrate Easy on spray nozzles; can Cannot be mixed dry.(EC) A liquid formulation, be used with small amountsoil that makes an emulsion of water; easy to suspend inwhen mixed with water. water; very little residue left

in bottom of tanks. Not dusty.

Wettable Powder—pesticide Can be mixed dry. Abrasive to nozzles.is mixed with clay carrier Difficult to keep suspended inused for suspending in water. water; much can end up wasted on

bottom of tank. Dusty.

Flowable—a wettable Reduced dust as compared to Still abrasive to nozzles.powder that has been mixed a wettable powder.with a liquid to makehandling easier.

Dust—a pesticide mixed Coverage can be seen and Dusty, dirty. Leaves a lot of visiblewith dust used as a carrier; evaluated. residue.very dilute compared to awettable powder.

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the other rubber tube near the insect. Itwill be pulled inside of the jar for lateruse. Be sure to place the netting over theend of one tube or you may end upeating your samples!

Conclusion

Pesticides are an important part of anyIPM program, but they also havedrawbacks and should be used as a lastresort after other types of controls havebeen put in place. They must be used ina responsible manner, not only from asafety and environmental standpoint,but also to ensure their continuedeffectiveness. A plan must be devisedusing monitoring and economic injurylevels. The safest and most effectivematerials and formulations must beused, in the proper manner, and theireffectiveness ensured through testing.

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Laws Regulating PesticideApplication

The Federal Insecticide, Fungicide, andRodenticide Act (FIFRA) requirescertification and licensing of users ofrestricted-use pesticides. Certificationdocuments the fact that applicators/handlers know how to use pesticidessafely for themselves, the public, and theenvironment. There are two categoriesof applicators: private and commercial.A private applicator is a person who usesor supervises the use of pesticides for thepurpose of growing an agriculturalcommodity such as mushrooms. Theapplication can be done on propertyowned or rented by the applicator or theapplicator’s employer. A commercialapplicator is a person who uses orsupervises the use of pesticides on a“for-hire” basis. State pesticide inspec-tors with both the Pennsylvania Depart-ment of Agriculture and the DelawareDepartment of Agriculture routinelyconduct on-site use observations toensure that applicators are handlingpesticides correctly. Review the safetytips below in preparation for thepesticide inspector.

B. Pesticide SafetySusan Whitney

The Worker Protection Standards(WPS) cover workers and pesticidehandlers/applicators in mushroomproduction. (Workers are those employ-ees who do any kind of work that wouldbring then in contact with surfaces thathave been treated with pesticides in thepast thirty days.) All pesticides used inmushroom production must have an“Agricultural Use Directions” statementon the label. Read this statement toensure that you are complying with thelaw. For specific details on WPS, consultthe “EPA How-to-Comply Manual.”The WPS requires employers to providethe following for both workers andhandlers/applicators:

1. Information at a central locationthat includes a WPS safety poster;the name, address, and telephonenumber of the nearest medicalfacility; and the name, date, time,restricted entry interval (REI), andapplication site of pesticidesrecently applied.

2. Training for workers and handlersunless they are already certifiedapplicators.

3. Transportation to an appropriatemedical facility, as well as pesticideuse information if a pesticide illnessoccurs.

4. Decontamination sites within 1/4

mile of all workers and handlers.Supplies must include water forroutine washing—one gallon perworker and three gallons perhandler (in some cases, eye flushwater must be immediately avail-able for handlers); plenty of soapand paper towels; and cleancoveralls for handlers.

The WPS requires employees to providethe following for handlers/applicators:

1. Personal protective equipment(PPE) required by the pesticidelabel (Figure 16). Employers mustconfirm that all equipment is clean,is inspected for damage, and isworking properly. PPE must bestored away from pesticides.

2. A pesticide-free area for changingclothes.

3. A decontamination site for washingafter handling tasks and at mixing/loading sites. Employers mustmonitor handlers who are usingfumigants or any pesticide that hasa skull and crossbones on the label.

4. Specific instructions on the pesti-cide label, including how to useapplication equipment. Employersmust inspect and maintain applica-tion equipment. Employers mustprovide access to labels.

Figure 16. Applying pesticides using typical Personal Protective Equipment.

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The WPS requires employers to do thefollowing for workers:

1. Notify workers about applicationsand areas under REI. Employersmust post written signs that meetEPA standards. Some products mayrequire both signs and oral warnings.

2. Keep workers out of areas wherepesticides are being applied.

3. Keep workers out of areas underREI, except for early-entry excep-tions.

Mushroom producers also may have tocomply with the Occupational Safetyand Health Administration HazardCommunication Standard. This lawrequires employers to make MaterialSafety Data Sheets on all hazardouschemicals in the workplace, not justpesticides, available to employees.

The Federal Record Keeping Regula-tions require that private applicatorskeep application records of restricted-use pesticides. Records must include thepesticide name, EPA registrationnumber, total amount of active ingredi-ent applied, size of area treated, com-modity, location of application, andcertified applicator’s name and number.Records must be made within 14 daysof the application and kept for 2 yearsin an easily retrievable format. Theymust be surrendered to medical person-nel upon request. Pennsylvania requiresthese records to be kept for 3 years.

The Worker Protection Standards coverboth restricted-use and general-usepesticides. They require producers tokeep application information in acentral location where workers normallycongregate. Information must includethe pesticide name, EPA registrationnumber, time of application, and re-entry date and time. Pennsylvania alsorequires records of the formulation and

rate of application for all uses of anypesticide with an REI on the label.Records must be made before theapplication and kept for 30 daysfollowing the REI. This form satisfiesboth WPS and the Federal RecordKeeping Regulations.

Safe Handling ofPesticides

Pesticide labels should be read at leastfive times: before buying a pesticide;before storing a pesticide; before mixingand loading; before applying thepesticide; and before disposing of theempty container and/or unwantedproduct.

Keep in mind that the label is the law! Itis a legal document. If label directionsare not followed, the law has beenbroken—an action that may warrantfines and/or penalties. The label tellshow toxic the pesticide is, what PPE towear, and how to protect the publicfrom exposure and the environmentfrom contamination. The label also tellshow, where, and when to apply theproduct and what pests are controlled.

Probably the most important words onthe label are the signal words, whichindicate how toxic the product is to theapplicator: Caution—least toxic;Warning—moderately toxic; Danger—most toxic. Remember this equation:Risk = Toxicity x Exposure. Your risk ofbeing poisoned by a pesticide is equal tothe toxicity of the product times yourexposure to the product. Never use aproduct with a danger signal word if aproduct with a warning or cautionsignal word will get the job done just aswell. The product with the dangersignal word will not kill the pest anyfaster, but it will be more hazardous tothe applicator’s health.

Pesticides can enter the human bodythrough contact with the skin, inhala-tion, or ingestion. For protection fromexposure to pesticides on your skin, readthe PPE statement on the label. Wearthe recommended chemically resistantgloves and coveralls. Clean and main-tain PPE according to manufacturerdirections. Check regularly for signs ofwear and tear. The minimum PPErequired for any pesticide application isa long-sleeved shirt and long-leggedpants. Of the contamination that landson a person’s body during mixing andloading, 98 percent ends up on thehands and forearms. This contamina-tion is avoided easily by wearing long-sleeved shirts and gloves. For protectionfrom breathing pesticide fumes andvapors, read the PPE statement on thelabel. Wear the recommended respiratorand clean and maintain it regularly.Have a respirator fit-test each season. Toprotect against ingesting pesticide, nevereat, smoke, or drink while handlingpesticides. Wear a face shield whilemixing and loading to prevent danger-ous splashes.

If transporting pesticides from thedealer to your place of business, keepthe pesticides in the bed of a pickuptruck. Never carry pesticides in thepassenger compartment of a vehicle. Tiethe containers down and carry anemergency spill kit. Long-term storageof containers should be in a locked, dry,well-ventilated facility that is free fromtemperature extremes. A sign on thedoor should warn that pesticides arestored inside. In case of fire, emergencypersonnel need to know that toxicfumes may come from this room. Thefloor of the storage facility should bemade of sealed concrete for easydecontamination after spills. Anyshelving should be of stainless steel, aswooden shelves will soak up spills fromopen containers. Fumes from such spills

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will continue to contaminate any visitorto the room.

Place open containers in secondarycontainers. Disposable “turkey roasters”from a department store work well.Never keep food, feed, seed, or businessproducts in the pesticide storage facility.Absorbent materials like stationary andpaper towels will absorb pesticide fumesand contaminate users repeatedly. Neverstore PPE in the pesticide storagefacility for the same reason. Keep a spillcleanup kit handy: broom, dust pan,mop, bucket, bleach and lye (fordecontamination), and spill controlproducts. Cat litter will soak up a spilleasily. Newer products made of gelflakes will pick up the spill and allowyou to transfer it to the spray tank forapplication. (Gel flakes will not clogapplicator nozzles.) This means that it isnot necessary to dispose of a valuablepesticide or hire a hazardous wastecontractor to clean up a spill.

Proper calibration of applicationequipment will save money by avoidingproduct overuse. In addition, calibra-tion prevents loss of commodity fromexcess pesticide residue. Fill a spray tankwith water and put the nozzle in abucket to collect the spray. Run thesprayer for the amount of time it wouldtake to spray one bed. Measure theamount of spray collected in the bucket.If this is more pesticide than the labelrecommends for one bed, it will benecessary to move the spray wand fasterover the bed. If the amount collected inthe bucket is less than what the labelrecommends for one bed, it will benecessary to spend more time applyingthe product to ensure adequate cover-age.

While mixing and loading, wear thecorrect PPE. Connect a backflowpreventer to the hose to prevent back-siphoning and contamination of thewater supply. During the applicationprocedure, make sure that no workersare in the area. Wear the label-requiredPPE for the application, and let some-one know you are working withpesticides in case of an accident. Cleanthe spray tank after each use or use adedicated sprayer.

After the application, triple rinse or jetrinse empty containers. Take thecontainers to a pesticide containerchipping facility to recycle them. Checkwith the appropriate state departmentof agriculture to determine availabilityof chipping facilities. Unwantedpesticide can be disposed of by use on-site, or a hazardous waste contractormay be hired to remove the unwantedproduct. Avoid the problem of un-wanted pesticide. Buy only what can beused in one season or less. Stockpilingof inventory is not recommended,because the EPA may cancel a productbefore one that is in storage is used.Likewise, the manufacturer mayproduce a better pesticide than aninventoried chemical, or stored productsmay become obsolete on a particularfarm because of a change in the farm’spest complex. There are many reasonsfor buying pesticides in small quantitiesand using stock quickly, not the least ofwhich is that improper storage anddisposal of empty containers andunwanted product can contaminate theenvironment.

Following pesticide application, showerand put on clean clothing. Washapplicator clothing on-site, or usedisposable PPE. If clothing must betaken home, wash it separately fromfamily wash.

In the case of a pesticide emergency,read the information posted at thecentral facility, which will include thelocation of the nearest emergencyfacility. Clipboards with emergencyprocedures should be kept in pesticidestorage facilities and in mixing/loadingareas. All workers should be familiarwith, and review often, the informationposted on the clipboards.

Sciarid Flies

The major insect pest of mushrooms inNorth America is the sciarid fly,Lycoriella mali. These flies are smallblack insects about 1⁄4 inch (3–5 mm)long with long antennae and gray wingsheld folded over the back (Figure 17).Females are more abundant and largerthan males. Female sciarids have apointed abdomen that is frequentlyswollen with eggs, while males haveprominent claspers on the end of theirabdomen that are used in mating.Females are attracted to lights andfrequently can be seen on backlitwindows, vents, picking lights, andblack light traps. This attraction to lightprovides the grower with a means to

monitor the number of female fliesentering the house and emerging fromthe compost/casing during the crop.Males, on the other hand, are foundprimarily on the surface of the casingsearching for newly emerged females tomate with. Adult flies do not activelyfeed but may take in some water. Theimmature sciarids (larvae) are translu-cent, white, legless maggots that rangein length from 1⁄8 to 1⁄4 of an inch (1–8mm). The head is large and dark withpowerful chewing mouthparts thatdistinguish sciarid larvae from otherinsect larvae that might be found inmushroom production houses. Thelarvae are the feeding stage in the lifecycle of this fly.

C. Pest Species Biology and Control

1. Arthropod Pests

Clifford Keil

Figure 17. Sciarid fly and larva.

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Sciarids like L. mali are found naturallyin cool shaded woods and areas of densevegetation. The females seek out spotsto lay their eggs where fungi have justbegun to colonize the substrate.Accordingly, L. mali females invademushroom production houses as thecompost cools down after peak heatingand the mesophilic fungi in the com-post begin to grow. This invasioncontinues during spawning. It isessential to protect the crop by placingplastic on the bed surfaces and keepingthe doors and other entry points closedduring this period. Running black lighttraps during this period is a good way toassess the tightness of fly exclusionmeasures and also pinpoint the time ofinvasion. Female sciarids are capable offinding cracks to enter voids in blockwalls to find entry into rooms withrunning spawn. They are very tenacious.Adult L. mali prefer cool temperaturesand are most active when outdoortemperatures are between 50°F (10°C)and 75°F (24°C). Consequently, thethreat of infestation is greatest fromMarch to July and September throughlate November in most of NorthAmerica. This threat is diminishedduring the hottest part of the summer,especially under dry conditions andafter three successive frosts.

Once inside a growing room, a femaleL. mali typically will land on compostclose to the point of entry to lay hereggs. Depending on how well fed shewas as a larva, she may lay up to 150eggs. Female L. mali can be verydiscriminating in choosing a spot foroviposition. They can detect residues ofDimilin and avoid laying eggs onsubstrate with this pesticide. They alsocan detect the presence of Trichodermaand will lay their eggs preferentially inareas contaminated with this fungus.The eggs are small, 1⁄16 inch long,translucent and white, and oval. Theymay be laid as singles or in large

clumps. The larvae hatch from the eggsafter about 4–6 days at regular composttemperatures (75–80°F, 24–27°C). Thefirst instar larvae begin feeding immedi-ately on mycelium and the compostitself. The larvae go through 4 instars toreach their maximum size of 1⁄4 inch,shedding their integument at each moltto get larger. This is a vulnerable stagein the life cycle, and some insect growthregulators are active only on moltinglarvae. The larvae are voracious feedersand attempt to eat anything they find intheir jaws as they move through thecompost and casing. This includes othersciarid larvae (they are cannibals) andother insect larvae they might encounterin the compost and casing. They preferto feed on developing mycelium andcompost as opposed to a dense mycelialmat. It is hard for the larvae to feed onmycelium in fully spawn-run compost,as it is water repellant and studded withcalcium oxalate crystals.

About 21 days after the eggs were laid,the larvae transform into pupae, thetransition between the larvae and theadult. This stage is inactive and does notfeed. Many times, the larva will spin asilk chamber to protect itself duringpupation. Pupation generally lasts abouta week. The males typically emerge 1–2days before their sisters. Because there isa narrow window for oviposition duringcooldown and spawning, the firstgeneration of L. mali emerges as adultsvery synchronously just before firstbreak. This synchronous developmentallows the grower to apply insect growthregulators and biological controls suchas nematodes to the most susceptiblelife stages of the insect by timingdevelopment from the peak invasion onlight traps. The complete life cyclerequires about 28 days at normalcompost temperatures. A peak ofemergence usually can be seen for thesecond generation, but it is less distinct.

There is evidence that the timing of thelife cycle for L. mali may change withdevelopment on different strains ofAgaricus bisporus, different species ofAgaricus (e.g. A. blazei or A. bitorquis),or different species of mushroom(Pleurotus or Lentinula). There havebeen reports that L. mali populationsthat have become resistant to certainpesticides may take longer to completedevelopment.

The feeding of larvae in the firstgeneration probably does little damageto the crop. The exception to this rulewould be in situations where Tricho-derma green mold is prevalent. In thiscase, it is likely that even small infesta-tions of flies can significantly magnifythe damage from this disease. Very highnumbers of larvae feeding in thecompost during spawn run also caninhibit fruit body production throughdestruction of the compost and themycelium. In most situations, cropdamage and loss of yield and qualityresult from the ability of the adults tomechanically spread mushroom diseasessuch as Trichoderma, Verticilliumfungicola, and Pseudomonas tolaasii. Thefeeding of the second generation larvaealso can be extensive and can result inyield loss through degradation of thecompost and casing, and destruction ofmycelium and fruit body primordia inthe casing. In severe infestations, larvaecan tunnel up into the stipe, resulting inthe condition referred to as “blackstem,” which renders the mushroomsunmarketable. The potential for cropdamage through reduced yield andquality is significant with this pest.Growers must be continuously vigilantto avoid crop damage from this insectpest.

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Phorid Flies

A pest of secondary importance inNorth America is the phorid fly,Megaselia halterata. These flies are small,1⁄

8 inch (2–3 mm) in length, with a

humpback appearance and very smallantennae (Figure 18). They appearstockier than sciarids and are veryactive, running and hopping erratically.The males and females closely resembleeach other. Adult phorids typically enterthe production rooms and houses laterin the crop cycle than sciarids. Theyprefer warmer air temperatures anddrier conditions in the substrate. Theyalso can become a problem later in theyear, typically June and July. Conse-quently, infestations of M. halterata aretypically seen in drier areas of casingafter second break. The larvae arecreamy-white maggots that are nolonger than 1⁄

4 inch (6 mm) when fully

grown. The rear end is blunt andcontains the opening of the breathingtubes. The head is pointed and the samecolor as the rest of the body. Themouthparts are relatively small hooksheld inside the head. Phorid larvae feedonly on mycelium and graze selectively.

Female phorids enter the growing roomand lay about 50 eggs in areas wherethere is fresh mycelia growth. The larvaehatch after several days and beginfeeding. They pass through three to fourinstars. They are more sensitive tovariations in compost and casingtemperature than sciarids, and thetiming of the life cycle is variable. Atwarm compost temperatures of 75–80°F (24–27°C), development from eggto adult may require only 15 days.During cropping with lower tempera-tures (60–70°F, 16–21°C) in the casing,development may extend up to 50 days.The larvae feed only for about 1⁄3 of thisperiod of immature development. Theremainder of the time is spent as theimmobile and nonfeeding pupa. Thepupae are about 1⁄8 inch long andgradually turn from cream colored todark brown as they mature. The pupaeare flattened and oval in shape withbreathing horns at the broad head end.

Because the larvae feed selectively, theyare not capable of causing the kind ofdamage that sciarids do as larvae.Significantly more phorid larvae can betolerated—perhaps as much as 50 to100 times more than sciarids—beforeeconomic damage can occur to the crop.Phorid adults are very capable oftransmitting fungal and bacterialdiseases, however, and control of theadults is necessary to maintain crophealth. Because they are active fliers,they can be a significant irritant topicking crews, and control of the adultsmay be necessary to maintain efficiency.

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Figure 18. Phorid fly and larva.

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Cecid Flies

A variety of other species of flies can beencountered in mushroom houses. Themost potentially damaging are cecidflies (Figure 19). Three species havebeen identified as pest species in theUnited States. These three species arerarely seen as adult flies, because undermost conditions larvae become “motherlarvae” that give birth directly to 10–30daughter larvae. These species usuallydo not become a pupa and subsequentadult that must mate before laying eggs.Reproduction is accomplished withoutmating and gives rise to daughter larvaedirectly. This is termed paedogenicparthenogenesis. When conditions areoptimal, this method of reproductioncan result in very rapid multiplication ofthis pest, leading to astronomicalnumbers of larvae, tens of thousands persquare foot.

Cecid larvae are legless maggots, bluntlypointed at both ends. The head and thetail are not easily distinguished, exceptby the direction of travel. White larvaetypically are the species Heteropezapygmaea, while orange larvae are in thegenus Mycophila, either speyeri orbarnesi. Heteropeza pygmaea is probablythe most commonly encountered cecidin mushrooms and has been reportedfrom Agaricus as well as other species,particularly Pleurotus. The small, stickylarvae are spread by workers and ontools and equipment. Initial entry to thegrowing room may be by transport ofinfested peat or substrate, movementwith personnel, or through the rareflying adult. Small infestations may notbe readily apparent at first. The larvaefeed on the mycelium as well as on thestipe and gills of mature mushrooms. Iflarge populations develop, the larvaemay mass together on the floor anddisperse in large groups. Larvae also canbe found on mature mushroom capspacked for market. This species has thepotential to significantly reduce yieldwhen it becomes established on a farm.

The two orange Mycophila are not ascommon as the white Heteropeza, butcan cause significant damage. They havea slightly shorter life cycle and thereforecan develop damaging population levelsrapidly. However, their orange colormakes them more conspicuous, andgrowers typically notice them beforelarge populations are attained.

Cecid larvae have the potential offeeding on mycelium within woodenstructures inside growing rooms.Because the wood offers some insulationfrom the heat of cookouts, they maysurvive the high temperatures and infestthe next crop. Direct treatment of woodwith insecticides and fungicides may benecessary to reduce between-cropsurvivors if there are high populations ofcecids on the farm.

Figure 19. Cecid fly and larvae.

Other Flies

A number of other species of flies maybe noticed by alert growers, especiallyon light traps. Most of these areincidental and may indicate that certainconditions can be found in growingrooms that require attention. Occasion-ally, they indicate the presence of a newpest on the farm. When in doubt aboutthe identity of insects found on thefarm, do not hesitate to submit samplesfor identification.

Flies that resemble a large phorid withprominent red eyes are probably fruitflies in the genus Drosophila. The term“fruit fly” is a misnomer for this group,as the larvae all feed on fungi of one sortor another, in some cases on rottingfruit. In the wild, larvae of these fliescan be found feeding on maturesporophores in great numbers. Theselarvae resemble small house fly maggotsin that they have a pointed head withsmall mouth hooks and a blunt rear endwith breathing tubes. If we think ofsciarids and phorids as feeding on theearly stages of mycelial growth in the lifecycle of a fungus, we can think ofDrosophila as feeding late in the lifecycle. If you see significant numbers ofDrosophila adults, there are probablyareas in the growing room with large,over-mature mushrooms. This can be aproblem particularly in portobelloproduction if large, nonmarketablemushrooms are not picked off the bedpromptly. The danger here is that iflarge populations develop, eggs may belaid on mushrooms packed for sale. Ifthe eggs hatch and larvae begin feedingduring transit, storage, and display inthe retail store, consumers may purchasemushrooms with maggots in the cap.

Other species of flies may indicate thatanaerobic conditions may have devel-oped at some place on the farm or ingrowing rooms. These flies includeblack scavenger flies (sepsids), moth flies(psychodids), and small dung flies(spherocerids).

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Introduction

There are many fungal pathogens ofmushrooms, but only a few of themcurrently affect commercial mushroomfarms. Some of these are true pathogensattacking the mushroom mycelium,while others can simply outcompetemushroom mycelium growth. Fungalpathogens can either affect the qualityof the product, reduce production, orboth. But all of them reduce the totalreturn of a crop, often significantly.Many control methods, such as sanita-tion, are useful for all of the diseases.There also are control measures specificto each disease.

Verticillium Diseases

Common names:Verticillium disease, Verticilliumspot, brown spot, fungus spot, drybubble

Scientific name:Verticillium fungicola

Outdated names:Verticillium malthousei,Acrostalagmus fungicola, Cepha-losporium constantini

Perfect stage:unknown

Verticillium is one of the most signifi-cant diseases of commercial Agaricusproduction. It is endemic on manymushroom farms and can cause substan-tial yield reduction. It can occur innature in addition to cycling within amushroom farm, traveling from older tonewer growing rooms.

C. Pest Species Biology and Control

2. FungalPathogens

Phillip S. Coles

William Barber

Identification

Infection takes on a variety of forms andhas various symptoms, from smallspotting on the surface of a mushroomcap to a complete infection of thefruiting body so that it is unrecogniz-able as a mushroom. Appearance willdepend on the timing of infection andthe number of spores.

The first symptom group is spotting, asuperficial infection causing necroticlesions on the cap of the mushroom.These spots will enlarge and coalesce asthe mushroom enlarges. This easily canbe confused with bacterial blotch orTrichoderma spot. Spotting is the resultof late infections of Verticillium. Themushroom already had developed whenthe infection occurred, and the patho-gen only had time to infect the mush-room superficially.

A simple way to determine whichorganism is causing spotting is to placeinfected mushrooms into a sealed plasticcontainer with a few moistened papertowels. The water in the towels will keepthe humidity of the chamber high, andthe causal agent will grow out from themushroom tissue. If the infection isbacterial, the color of the spots will notchange. Trichoderma spot, on the otherhand, will turn green when the fungussporulates, and Verticillium will turn themushroom surface gray and give it afuzzy texture.

A very localized infection on themushroom cap can be expressed as a“harelip.” The infection kills the cells ina specific area, preventing growth.Then, while the other cells of the capcontinue to grow, expansion occurseverywhere except within the infectedarea. This causes the pinched area, orharelip. The dead area of the sporocarpwill appear gray and leathery.

Infections on the mushroom stem willcause exterior cells to die. Because theexterior cells no longer will grow whilethe noninfected cells continue toelongate, the mushroom will bendtowards its infected side. Further, thedead cells will split and crack, causing a“blow out” (stipe blast) on the side ofthe mushroom stem. An infection onthe stem also can be expressed as astreak along the length of the stem.

More significant infections cause seriousdeformation of the sporocarps, whichwill appear as large, formless, puffball-like masses. The cap becomes indistin-guishable from the stem (Figure 20).Growers commonly refer to thissymptom as “dry bubble.” Its expressionrequires early infection by Verticilliumspores. The Verticillium spores musthave infected the pins early enough, andwith enough spores, to have time tocompletely take over the growth of thepin. Bubbles will be covered with thegray fuzzy bloom of the Verticilliumconidiophores.

Figure 20. Verticillium in the dry bubble stage.

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Biology

Verticillium spot (Figure 21) takes about7 days to produce visual symptoms. Ifthere are visible lesions, stipe blast, orother superficial mushroom deformities,it can be concluded that Verticilliumspores infected that mushroom about 7days before the appearance of symp-toms. For an actual bubble to appear,the infection requires a 10- to 14-dayincubation period. Therefore, if themushroom pin already is formed at thetime of infection, there will be onlysuperficial markings on the mushroom.If the infection begins soon after casing,dry bubbles will be formed.

Verticillium needs the developingsporophore to manifest symptoms. Themycelium germinating from theVerticillium spores will grow into themushroom tissue, parasitizing anddeforming it. Mushroom myceliumalone will show no symptoms ofVerticillium.

Verticillium infections are caused byspores and mycelium transported or

spread to uninfected sites by manydifferent modes. The spores are verysticky and can be carried by anything towhich they are able to stick. Thisincludes, but is not limited to, person-nel and their clothing, mushroom flies,mites, and rodents. Flies are particularlyproblematic vectors, since they activelyare trying to leave older growing rooms.Flies likely will pick up Verticilliumspores in the older rooms and spread theinfection to new rooms. In addition,they can carry mites that in turn cantransport Verticillium spores.

Once the mites leave the bodies of theflies, they will spread spores whilemoving throughout the room. Rodentfur is an excellent carrier for the stickyspores, and the tendency for mice andrats to bore into mushroom beds insearch of spawn grains can expose a lotof material to infection. Equipment canbe a source of inoculum, especiallyequipment that is moved from dirtyareas to clean areas. A good example iswatering or spraying equipment.Watering and spraying are donethroughout the crop, and if a watering

nozzle or hose is used at the end of acrop and then moved to an earlier stage,infection can result. Harvesting basketstraveling to and from a processor alsocan be a source of inoculum if thebaskets are delivered from an infectedgrowing area to the processing plant andare returned to the farm—or deliveredto another farm—where they mightinfect a previously clean growing area.

Verticillium can be spread on aircurrents. Spores will stick to dustparticles and can enter a growing roomthrough the ventilation systems. Dustcan settle on equipment or casingmaterials en route to a room. Sporesalso can travel on airborne mites,regardless of whether or not the mitesare living.

The initial infection may come fromone of many sources, but once inside aroom, the infection can spread veryquickly. This is due to the high repro-ductive capability of the Verticilliumorganism, which can produce 30million spores per hour. Tests on petriplates have shown that, after touchingone bubble that is sporulating, a fingercan touch eight more petri plates andcause infections on every plate. There-fore, anything contacting a sporulatingbubble can infect many potential sites.High fly populations are very effectiveat spreading an infection throughout aroom. Water hitting an infected site canpick up spores and splash them ontoother mushrooms, infecting them withVerticillium. Harvesters and theirequipment will spread an infectionquickly throughout a growing room, aswell as from room to room.

High spore loads can develop on thefloors and other infection sites, increas-ing the possibility of spores beingpicked up by a vectoring agent. Deadmushrooms also can be reservoirs forinoculum.

Figure 21. Verticillium spot.

Monitoring

The most useful method of monitoringVerticillium is to count the number ofbubbles in a growing room. By mappingthe number and location of the bubbles,you can detect patterns. Improperlysanitized casing equipment may showitself in a high concentration of bubblesin the area where the casing crew starts.High bubble counts in rooms havingthe highest incoming fly populationscould indicate spores coming in withflies. High bubble populations neardoors might suggest that dust isentering through doorways or that thereare possible ventilation problems.

Understanding the timing of Verticil-lium disease is essential for controllingit. The time when a specific symptommanifests itself is a good indication ofwhen the infection occurred. If bubblesappear on first break, for instance, thereprobably was a breakdown in sanitationin the peat moss preparation, the casingoperation, or an early stage of casegrowing, since there is a 10- to 14-dayincubation period for bubble develop-ment. If bubbles do not occur until thelast break, it is likely that spores areentering once harvesting has begun,either on harvesters or harvestingequipment.

Control

Verticillium control depends primarilyon eliminating spores through sanita-tion and control of vectoring agents. Allequipment should be kept in dedicatedstorage areas. Equipment and personnelfrom dirty areas never should be allowedto enter clean areas, and personnel andequipment from clean areas nevershould be allowed into dirty areas. Ifhoses or spray apparatus, for example,must be moved between clean and dirtyareas, they should be moved fromnewest to oldest rooms, then sanitizedbefore they are returned to new rooms.(See “Sanitation” in Chapter II.A.2,Cultural Control.)

Harvesters must be trained to recognizeand not touch bubbles. More impor-tantly, employees must be taught theimportance of cleanliness, particularly ifthey work in clean areas. Control dustby paving roads or by oiling or watering

gravel roads. Filter air to exclude sporesand anything that may be carryingthem, such as flies or mites. (SeeChapter II.A.1, Exclusion.) Control flyand mite populations and their move-ments into new growing areas. (SeeChapter II.C.1, Arthropod Pests.)

Bubbles can be destroyed with salt. Thebest method is to put salt into a plasticdrinking cup, then cover the bubblewith the cup and salt (Figure 22). Thesalt will desiccate the bubble, preventingfurther mycelium growth, and theplastic cup will prevent the spores fromspreading. Bubbles can be physicallyremoved from the growing room. Thisis often done in an alcohol solution.The procedure is risky, however, sincethe bubble is disturbed and sporesmight be released. Worse yet, the personremoving the bubbles can become adisease vector.

Figure 22. Salt will kill the Verticillium, while the cup will prevent the spread ofspores.

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Fungicides have been, and most likelywill continue to be, available for thecontrol of Verticillium. There is,however, a special difficulty with tryingto develop a fungicide for a fungalpathogen of a crop that is itself afungus. Very often the fungicide willhave a toxic effect on mushroomgrowth. This must be weighed againstthe benefit of Verticillium control, sincesome mushroom production could belost. Also, since pesticides that are theleast deleterious to the mushroom cropmust be used against Verticillium, thefungicide’s mode of action against drybubble must be targeted to one of thefew things that is different aboutVerticillium and Agaricus. Since mush-rooms and Verticillium are very similarfrom a pesticide’s point of view, anydifferences between the two that areexploited by a pesticide’s mode of actionwould be small, and there would be astronger propensity toward the develop-ment of resistance than normally occursin most pest species. Therefore, pesti-cides should be used sparingly, onlywhen needed, and according to eco-nomic thresholds (See Section I.B).

In some instances, despite whatevercombination of control measures areused, Verticillium can run rampantthroughout a growing room. Sometimesit is possible for every developingsporophore to be expressed as a bubble.In this extreme example, there is nopoint in continuing the crop, especiallyif no harvestable mushrooms are beingproduced. The room will have becomean incubator for Verticillium spores andmost likely will be producing flies thatwill further spread the spores and thoseof other molds. Trying to save old cropswith this level of infestation will resultin the continuation of the infectioncycle. Steam the room early andeliminate this potential source ofinoculum.

Trichoderma Green Mold

Common name:green mold

Scientific name:Trichoderma harzianum

Perfect stage:unknown

Trichoderma harzianum is a relativelynew disease of commercial mushroomproduction. It was first encountered inIreland and the UK in 1985. Duringthe 1985–1986 growing season, theensuing epidemic caused losses esti-mated at one million monetary pounds($l.5 million U.S.). Through 1990,losses were estimated to be between 3and 4 million pounds ($4.5–6.0 millionU.S.). In 1990, it appeared in BritishColumbia, and in the Ontario area in1992. In 1993, it reached the BerksCounty growing area of Pennsylvaniaand, in 1994, Chester County, Pennsyl-vania. Since then, it has becomeendemic in Pennsylvania.

Aggressive strains of Trichodermaharzianum have been associated withthe commercial production of Agaricusbisporus. In the UK, the aggressive formis known as “Th2.” In the U.S. andCanada, “Th4” is the dominantaggressive strain. These aggressive strainshave been found only on mushroomfarms and only recently.

The genus Trichoderma includes manycommon soil-inhabiting fungi anddecaying organisms associated withwood and decaying vegetation. Innature, it has an important role as adecomposer. Trichoderma is a verycomplex genus, and not until 1969 didRafi properly clarify the taxonomy.Nine species aggregates were identified

from their microscopic characteristics,but to date there is still no satisfactoryclassification of species in Trichoderma.In addition, there are many differentstrains or races in the various species.They can vary in aggressiveness,resistance to heat or pesticides, and in avariety of other ways.

Trichoderma species are asexual fungithat propagate through vegetativegrowth and production of asexual spores(conidia). The conidia are spread easilyby various means. Trichoderma also canhave a sexual stage in which its appear-ance is changed so substantially that itoriginally was classified incorrectly asbelonging to the genus Hypocrea.

The members of the genus Trichodermahave a considerable arsenal of “chemicalweapons” that are produced in the formof antibiotics and other toxins thatstrongly inhibit the growth of otherorganisms. Furthermore, some speciesare capable of parasiticism on themycelium of other fungi. Its aggressive-ness makes it useful as a biologicalcontrol agent against fungal pathogensof green plants. This same aggressive-ness, however, makes it a seriouspathogen in commercial mushroomproduction.

It is now possible to isolate differentspecies and strains through PolymeraseChain Reaction (PCR), but when firstencountered, green mold samples had tobe identified through microscopicexamination that was very time-consuming and always suspect as toaccuracy. PCR examination also hasshown that green mold is not a newstrain of Trichoderma that mutated froman existing form, nor is it one of manystrains developed for biological controlson green plants. It probably has beenaround for millions of years, andchanges in cultural practices made itvery successful in mushroom houses.

Beyond mushroom farming, it is veryrare.

Trichoderma mycelium grows oncompost and competes aggressively withmushroom mycelium. Microscopicobservation of the interaction betweenTrichoderma and mushroom myceliumdoes not show any obvious pathogenic-ity. This has lead to debate aboutwhether Trichoderma green mold is afungal pathogen or a competitor.

Identification

Trichoderma mycelium is gray in thebeginning and then changes to white,becoming very dense. After fruiting, itsspores turn it a dark green (Figure 23).There are many other types of moldsthat also are green and associated withmushroom compost, includingGliocladium, Cladosorium, Asperigillus,Penicilium, and Chaetonium. Care mustbe taken not to confuse them withgreen mold. There also are other speciesand varieties of Trichoderma that willnot cause the disease, and only throughclose taxonomic examination orthrough PCR can they be differentiated.However, if green mold progressesrapidly across the growing surface(Figure 24), it can be assumed to be oneof the aggressive varieties of Trichodermagreen mold.

Pygmy mites often are associated withgreen mold infestations, though this isnot always the case. They also can occurin the presence of other types of fungi.

Figure 23. Trichoderma mycelium, showing dark green color.

Figure 24. Widespread green mold infestation.

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Biology

To infest a mushroom crop, Trichodermafirst must have its spores introduced.The spores are contained in a stickymatrix that can attach to many differentsurfaces. Consequently, many of thetraditional pathways of other types offungi also apply to green mold. Thespores can adhere themselves to employ-ees and their clothing, as well as toequipment used on the mushroomfarm. Rodents can carry spores, andspores can travel on flies or on mitescarried by flies. (Mites are excellentvectors because they have specializedorgans known as sporangia, which areused to spread fungal spores.) Mush-room trimmings can be a reservoir forspores, and the practice of puttingtrimmings in compost can add toinoculum sources. If post-harvest andPhase II pasteurization are insufficient,green mold spores can survive to infest anew crop.

It is not enough for spores simply to bepresent; they must exist in sufficientnumbers and correct conditions mustprevail. No specific compost or environ-mental conditions have been found tobe associated consistently with greenmold development. It has been shownthat a carbohydrate source is necessaryfor spore germination. Spawn grainsserve the carbohydrate requirement verywell if they are fresh (the mycelium hasnot yet grown into the compost) and ifthe green mold spores are within onecentimeter of the grain. Green mold,therefore, will not germinate in fullycolonized compost, where the mush-room mycelium protects the grain fromthe disease. Green mold spores intro-duced at casing will not germinate forthe same reason. Also, a minimumnumber of spores are required. Theo-retically, only one spore is needed tostart a green mold infection; but, as istrue with most types of fungi, one spore

is not enough. Grogan showed that it ispossible to get an infection from lessthan 100 spores, though normally moreare needed. For experimental purposes,at least 9 million spores are used in eachinoculation.

Once germinated, the green moldmycelium will move quickly intocompost and colonize it. Consequently,mushroom mycelium no longer will beable to grow there. The green mold thenwill move into compost already colo-nized by mushroom mycelium and willspread across an entire growing surface.

Monitoring

Use the Verticillium mapping techniqueto monitor green mold; i.e., count thenumber of squares infected with greenmold in a growing room and map thenumber and location of the infections.By noting the number and location, youcan detect patterns. Improperly sani-tized spawning equipment may showitself if the highest concentration ofgreen mold is in the area where thespawning crew starts. High green moldcounts in rooms or in areas of a roomhaving the highest incoming flypopulations could indicate that sporesare coming in with flies. High greenmold populations near doors couldindicate that dust is entering throughdoorways or that there are possibleventilation problems.

The time at which a specific symptommanifests itself is a good indication ofhow severe the infections were atspawning. If no green mold is detectedexcept for a few spots at the end of thecrop, the amount of inoculum probablywas low. If it is seen when the plastic ispulled at spawn run, there was a seriousinfestation.

Control

Control begins in Phase I and Phase IIcomposting, where the number ofspores in the compost must be mini-mized. Any green mold spores that mayget into the compost during these stagesmust be destroyed to prevent germina-tion in the growing rooms after theroom is planted.

Minimize potential inoculum sources bynot allowing unpasteurized materialsfrom harvesting, such as mushroomtrimmings, onto the compost wharfwhere green mold spores could collectin the leachate pond. It is better toremove all trimmings from the farm siteif possible.

To eradicate spores that may get intothe compost, cross-mix during Phase Iso that all the material is exposed to thehighest composting temperaturespossible. Control moisture to ensurethat the maximum amount of compostreaches these temperatures. Formulateso there is a distinct ammonia odor atthe end of Phase I. The ammonia willhelp to degrade the exterior of the sporecoat.

Phase II pasteurization must be com-plete. Pasteurize at 140°F (60°C) fortwo hours. Beds must be filled uni-formly to ensure that all areas attain thistemperature.

Disease control depends primarily oneliminating spores through sanitationand control of vectoring agents.Sanitation at spawning is more impor-tant to control of green mold than, forinstance, control of Verticillium, whichis more dependent on control aftercasing. Harvesting and overall farmsanitation are important for control ofboth organisms. All equipment shouldbe kept in dedicated storage areas.Equipment and personnel from dirtyareas never should be allowed to enter

Dactylium Diseases

Common Names:cobweb mold, Dactylium mildew,soft mildew, soft decay

Scientific Name:Dactylium, cladobotryum

Outdated names:Dactylium dendroides, Nectriaalbertinii, Nectria rosella,Cladobotyium dendroides

Identification

Dactylium mildew, or cobweb mold, canbe recognized by its wefty, cotton-likemycelium. The mycelium will cover thesurface of the casing as well as thesurface of mushrooms and mushroompins. The mycelium is usually white,but can be gray and often turns pink oryellow with age. Infected mushroomsdevelop a soft, wet rot.

Cobweb mold is a relatively minordisease of mushrooms, but because of itsability to grow quickly, it can spreadover many mushrooms. If left un-checked, widespread mildew can resultin unsalable mushrooms and eventualsignificant yield loss.

Biology

Cobweb mold occurs only on the casinglayer and cannot grow in the compost.Therefore, infection must take placeafter casing. Symptoms can occur beforefirst break, but they usually appear laterin the crop. Dactylium may thrive in thecontrolled environment of a mushroomfacility, but it also can survive in wildmushrooms or in soil. Inoculum cancome from outside sources surroundinga mushroom farm or from older roomswhere infections have occurred. Unpas-

clean areas, and personnel and equip-ment from clean areas never should beallowed into dirty areas. If hoses orspray apparatus, for example, must bemoved between clean and dirty areas,they should be moved from newest tooldest rooms, then sanitized beforebeing returned to new rooms. (See moreon sanitation in Chapter II.A.2.)Control dust by paving roads or oilingor watering gravel roads. Filter air toexclude spores and anything that maybe carrying them such as flies or mites.(See more on exclusion in ChapterII.A.1.) To further reduce green moldspore spread, take the additional step ofusing separate cafeterias and breakrooms for employees working in areasother than harvesting. This also willhelp with other types of pathogens.Employees working in the spawningarea should be issued new uniformsdaily.

Areas infested with green mold can becontrolled with salt or hydrated lime bysprinkling the infected areas with eithermaterial. The salt or lime should extendat least 8 inches from the edge of thevisible growth, since adjoining casingcan harbor the mycelium and soon beproducing spores. If mycelium appearson the surface of the compost beforecasing, spray the area with a 1,000-ppmchlorine spray, again extending thetreatment 8 inches beyond theinfection’s visible edge.

Existing chemical pesticides essentiallyare ineffective on green mold myceliumonce it is growing actively in compost orcasing. However, it has been shown thatsome types of fungicides applied tospawn grains will provide limitedprotection to the grains and preventgreen mold spores from germinating.Tumbling the spawn with the fungicidemixed with a carrier such as gypsumcoats the grains. Great care must betaken when applying fungicides to the

spawn. First, spawn must be kept clean.In order to be mixed with a fungicide,spawn must be removed from itsoriginal packaging, exposing it topossible contamination. This couldresult in a worse green mold infectionthan if no fungicide had been applied.Therefore, sanitation is of the utmostimportance during this operation.

Second, tumbling the spawn in a mixerdamages some of the mushroommycelium on the spawn grains and canreduce its vigor. Mix the grains as gentlyas possible. Once it is mixed with thefungicide, spawn usually is stored in alarger bag than the original packaging.Therefore, care must be taken toprevent overheating of the spawn beforeit is applied to the compost. Of course,pesticide labels must be followed at alltimes.

Fungicide applications should belimited to avoid resistance development.They should be used as a “last resort”when green mold infestation is out ofcontrol. Sanitation is the only way tocontrol green mold in the long term,and once the disease is brought undercontrol, the use of fungicides must bestopped to reduce the chance ofdevelopment of resistant green moldstrains. (See more on resistance manage-ment in Section I.A and ChapterII.A.4.)

As with Verticillium, if green mold getsout of control, it is better to steam offthe room early rather than risk thespread of infection to new rooms.Reducing the amount of inoculum willyield benefits to future crops that aregreater than the benefits that might bereaped from the few mushrooms thatcould be salvaged. Post-harvest must beadequate.

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teurized soil or spent mushroomsubstrate used for casing can be a sourceof inoculum. Actually, any type ofcasing can cause infection if it hasbecome contaminated. Further, sporescan enter a growing room throughventilation or on employees or equip-ment. Infection often begins on deadmaterial left on the casing surface. Deadfruiting bodies or the stumps trimmedfrom mushrooms can be a food sourcefor germinating spores. From there, theinfection can spread to the casing layer,covering it and any mushrooms or pinsin its path. Infections can appearquickly and can spread rapidly. Trashleft on beds, high relative humidity, andhigh air temperatures are very conduciveto cobweb mold’s growth.

Control

Cultural controls, especially sanitationand exclusion, are the best way tocontrol cobweb mold. Casing areasmust be kept clean and sanitized.Casing material must be loaded intosanitized trucks and covered to preventcontamination during transport togrowing rooms. All equipment used forcasing must be cleaned and sanitized.Casing employees must be clean andwearing laundered clothing each day.Once the casing material is safely insidethe room, the air must be filtered toensure cobweb spores do not enter theroom (see Chapter II.A.1, Exclusion).Beds must be kept clear of trash such asstumps or dead mushrooms, whereinfections can start.

Environmental control is the key topreventing the spread of existinginfections, since cobweb mold needsboth high humidity and high tempera-tures to spread. Often, growers will raisea growing room’s temperature toaccelerate mushroom growth. A growermay be trying to outpace the growth ofa pathogen or trying to complete abreak on schedule. This practice can

cause more harm than good, for, if it isdone when cobweb mold is present, anepidemic may occur because the mold’srate of growth will increase faster thanthat of the mushrooms. Maintaining theoptimal temperature for mushroomgrowth, on the other hand, will bedetrimental to the growth of cobwebmold.

Since high humidity promotes thegrowth of cobweb mold, it is verysusceptible to control by desiccation ifgrowing room relative humidity islowered. Maintain the room tempera-ture below 65°F (18°C) and the relativehumidity below 92 percent, and thegrowth of cobweb mold will be inhib-ited.

Chemicals also may be used to controlcobweb mold, though presently thereare no materials registered specificallyfor it. Some fungicides applied for othertypes of pathogens such as Verticilliumhave the unintended but beneficialeffect of controlling cobweb mold.

Introduction

Weed molds may be defined as moldsthat grow in competition or in associa-tion with the mushroom mycelium.These fungi compete for nutrients andmay have a negative influence on thegrowth and nutrient uptake by Agaricusbisporus; however, they are not knownpathogens. Some weed molds may growin properly prepared compost forsupporting the mushroom’s growth,while others may not grow unless themushroom mycelium is present. Therange of effect that weed molds mayhave on the mushroom mycelium is broad.

Indicator mold are fungi that grow incompost that has not been selectivelyprepared for A. bisporus. Growth ofthese molds may suggest a nutritionalimbalance in the compost. Indicatormolds will grow only in compost thathas specific nutrient conditions thatfavor their development. These moldsgrow on compounds that the mush-room cannot use, and once that foodsource is depleted, these molds will stopgrowing and usually disappear. How-ever, because compounds were availableto these fungi, fewer nutrients areavailable to A. bisporus, and crop yieldusually is lowered.

Some of each type of mold have little tono effect on A. bisporus, while otherscan entirely inhibit the growth of thespawn and eventually the mushrooms.

Weed Molds

Lipstick Mold

Common Names:lipstick, red lipstick

Scientific Name:Sporendonema purptirescens

Outdated Name:Geotrichuin candidutti,Oosporum sp.

Lipstick mold may occur in compostduring spawn run or in the casingduring cropping. At first, this mold ishard to distinguish from spawn growth,as it first appears in spawned compost asa white crystalline-like mold. Growthbegins as small white colonies, previ-ously referred to as “frost on a wind-shield” or “small white cotton balls” onstraws or casing. When developing aftercasing, these small white balls may bemisidentified as mushroom spawnforming into pins. The descriptivelipstick color develops as the spores arematuring. Several shades of pink, cherryred, and eventually orange or buff colorsmay be found (Figure 25). It has beenreported that lipstick in a peat moss andlimestone casing remains white, and itsred color will not develop.

3. Weed andIndicator Molds

David M. Beyer

C. Pest Species Biology and Control

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Lipstick mold grows slowly and usuallyremains confined to areas of thecompost or casing. It does not appear togrow outward like green mold ormildew. The white growth of lipstickeventually may grow into uninfectedareas of casing, and it is able to colonizewell-conditioned compost. Significantyield losses are associated with heavycompost infestations prior to casing. Ifthe mold does not become visible untilthird break, yield loss will be minimal.

Air currents can spread spores fromcontaminated casing or spent compostduring watering or via pickers. Heavyinfestations usually reflect a build-up of

Figure 25. Lipstick mold causes a descriptive lipstick color as the spores are maturing. Several shades of pink, cherry red, andeventually orange or buff colors may appear.

spores around a mushroom productionarea. Poor sanitation and inadequatepost-crop steaming are possible causesfor an increase in spores around afacility.

An infestation of lipstick mold maycontinue for several crops or cycles on afarm. Control is achieved through acomplete post-crop steaming andadequate pasteurization during Phase II.The lipstick fungus may not be a provenpathogen of the mushroom, but itspresence indicates the need for increasedsanitation and pasteurization proce-dures.

It has been reported that the occur-rence of lipstick mold would indicatethat a La France virus disease mightalso be present. However, when virusoccurs, lipstick mold is not alwayspresent. This phenomenon suggeststhat the virus-infected and lipstickspores are spread around or intro-duced into an area in a similarmanner. Some of the control methodsfor this mold would be similar tothose for LaFrance disease.

It also has been suggested that theoccurrence of lipstick is related to oldwet poultry manure; wet, dense com-post at filling time; or excessive use ofsteam during Phase II. In addition,

colony becomes cinnamon-yellowbrown, the edges will remain white. Themold grows rapidly but usually disap-pears within 10 days or by the timemushrooms are first harvested. It ispossible that a dense infestation willretard the crop, especially first break,and cause a slight yield reduction.

The fungus, Chromelosporium fulva, isextremely common in soil and flour-ishes on damp wood. Under certainconditions, it can grow into casing notcolonized by spawn. Areas in compostthat overheated during spawn run,virus- or Trichoderma harzianum-infected areas, or areas of wet compostat fill with poor spawn growth encour-

excessive nitrogen at spawning time maybe related to increased lipstick mold.Excess nitrogen may be a result of thewet compost or excessive moisturecondensation with too much steam. Inthese latter cases, other molds also maybe present with lipstick. Wet compostor lumps of wet chicken manure maynot be completely pasteurized, andlipstick spores may survive.

Cinnamon Brown Mold

Common Names:brown mold, cinnamon brownmold

Scientific Names:Chromelosporium fulva,Chromelosporium ollare

Outdated Names:Botrytis crystalline, Ostrachodermapeziza

Perfect Stage:Peziza ostrachoderma (cup-shapedfruiting bodies)

Figure 26. Cinnamon brown mold starts out white, but changes color to lightyellow or golden brown.

Cinnamon brown mold has a variety ofcolor ranges, from yellow gold to goldenbrown to cinnamon brown. Cinnamonbrown mold is one of the most commonbrown molds found in mushroomhouses. The mold first appears as largecircular patches of white or gray-whiteaerial mycelium on the compost, casing,or on bed or tray boards. This moldmay grow on compost, but it is mostfrequently seen after casing. The moldstarts out white, but within a few daysspores form and the color changes tolight yellow or to light golden brown(Figure 26). Over time, the colordeepens to golden brown or cinnamon,and the mold develops a granularappearance. As the center of the mold

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age the growth of cinnamon brownmold. This mold has been observedgrowing on undistributed supplementsadded at spawning. Improperly condi-tioned compost containing green moldoften will contain cinnamon brownmold. Widespread infestations ofcinnamon brown mold may indicateeither poor sanitation or wet andimproperly conditioned compost.

The mold is most commonly known asa re-colonizer of over-pasteurized casingand spent compost. The mold will growrapidly from infested compost areas intocasing, especially in areas where spawngrowth is weak or nonexistent. It willgrow on the casing and can becomeobvious throughout much of thegrowing room at the same time,suggesting that airborne spores landedon the casing at about the same time.The high humidity and warm tempera-tures following casing are ideal forgrowth of cinnamon brown mold.

Several weeks after first appearance ofthe mold, and after the mold hasdisappeared, small cups or disk-shapedfruiting structures may appear on thecasing; these are the sexual phases of theC. fulva (Peziza ostrachoderma). Thecup-shaped structures have a rubbery orleathery texture and usually are darkbrown, although chartreuse and yellowfruiting bodies have been observed(Figure 27).

Figure 27. The cup-shaped structures caused by cinnamon brown mold have a rubbery or leathery texture and usually aredark brown, although chartreuse and yellow fruiting bodies have been observed.

during compost pasteurization and anadequate post-crop pasteurization areessential to eliminate the threat ofinfestation. Preventing spores fromentering mushroom houses duringspawning and the spawn-runningperiod is essential. High-efficiency airfilters reduce the possibility of introduc-ing the mold into spawning areas, andsanitary conditions should be main-tained during spawning.

Sepedonium Yellow Mold

Common Name:yellow mold

Scientific Names:Sepedonium spp., Sepedoniumchrysosporium

Sepedonium yellow mold begins to growas a whitish mold that eventually turnsyellow with age, and produces abundantspores that become easily airborne.Yellow mold differs from other yellow-colored molds by the appearance of thinwhite mold growing in compost duringthe spawn run and by the tremendousspore load that develops. The spore loadcauses clouds of “dust” when compost isdisturbed (Figure 28). The sparse whitemold turns dull yellow to tan with age.Yellow mold spores can be spread tocompost by air currents before orduring the filling operation, during thespawning operation or spawn-runningperiod, or because of spent compoststicking to wooden boards or trays.Spores also may survive pasteurizationin compost that is not conducive togood heat conduction and does notreach adequate temperatures.

The obvious, thick-walled spores ofSepedonium are resistant to the highheat of pasteurization; therefore, theyare able to survive Phase II. These sporesare spherical, golden brown, large, anddistinctly spiny, a characteristic thatdistinguishes Sepedonium from the othersignificant compost yellow mold,Chrysosporium. The latter causes matand confetti diseases. Sepedoniumproduces smaller oval spores, but theseare rarely observed in mushroomcompost specimens.

The growth of Sepedonium seems toaffect spawn growth—the moldcolonizes compost considered ideal forspawn growth. Heavy infestations ofSepedonium yellow mold are associatedwith poor yields, but whether this is dueto Sepedonium or to other factors is notknown. Sepedonium spore populationswill build up on a farm following theappearance of yellow mold. Stricttemperature monitoring and control

Figure 28. Yellow mold has a distinct yellow color in compost. The tremendousspore load of yellow mold causes clouds of “dust” when compost is disturbed.

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Pythium Disease

Scientific Name:Pythium hynosporum; Pythiumoligandrum

Outdated Name:Pythium artotrogus

Pythium is an antagonistic, potentiallypathogenic fungus infrequently isolatedfrom mushroom compost. The fungushas the potential to cause yield loss,because spawn will not grow in areascolonized by Pythium.

Toward the end of spawn run, perfectlyround areas may be noticed wherespawn does not colonize the compost.These distinct circular areas, which mayvary in size from a few inches up to 1–2feet in diameter, are characteristic ofcompost infested with Pythium. Thecompost immediately adjacent to theseblack areas may be well colonized withspawn and support a normal crop ofhealthy mushrooms. Occasionally, thecompost surface may be grown overwith spawn, but a lens or football-shaped mass of black compost, with thegreatest diameter in the center, may befound by digging into the compost. Atthe compost’s surface, only a small (2-to 3-inch) black spot may be seen, buton digging into the compost, thecharacteristic shape would becomeapparent. The compost may contain nosigns of a pest or pathogen except forthe sparsely growing delicate whitemold, which is Pythium. Eventually,spawn may colonize the infestedcompost; however, few if any mush-rooms will grow in these areas.

Microscopic examination and labora-tory study are necessary to identify awhite compost mold and confirm thepresence of Pythium. Often, otherdiseases or improper cultural practicescause spotty mushroom production.

Little information is available on the lifehistory of this fungus and the mecha-nisms by which it spreads throughout amushroom production area. Pythiumspores are large and thick-walled, andmay survive various heat and moisturetreatments. It has been reported thatthey are resistant to heat and drought.Viable spores have been recovered fromdry surface compost after Phase II, andspores can survive up to 18 months atroom temperature. Severe Pythiumdevelopment occurs after spores havebeen introduced to compost at or beforespawning. Airborne spores that con-taminate compost at spawning time arereported to be the primary source ofinfection. Therefore, filtration andreduced spore loads during Phase II andspawning will help to control this mold.Apparently, spores introduced a fewdays after spawning will not becomeestablished in compost and will notprevent spawn growth. Soil-laden strawor horse manure also are thought to besources of spores that survive pasteuriza-tion and then colonize within compost.Control also is accomplished withsound cultural practices such as effectivepasteurization of compost during PhaseII, a comprehensive sanitation programfor spawning, and a complete post-cropsteaming.

Corticium Mold

Common Name:Corticium-like (identity notcertain)

Corticium mold is found in compost,on casing, or on the woodwork ingrowing rooms. This flat-growing gray-white mold is found on straws or woodin mushroom houses. It appears to growfrom within beds or tray boards,uprights, cross pieces, and other woodstructures. When the mold grows oncasing, it looks granular like salt. Small1- to 2-inch diameter circles, occasion-ally covering up to 65 percent of thecasing, will be found. Corticium isfound infrequently today because ofeffective pasteurization and post-cropsteaming procedures. When this molddoes appear, it may tend to persist forseveral consecutive crops until it isconcurrently eliminated from infestedwooden surfaces and compost.

Overly decomposed—but not necessar-ily wet—substrate is associated with thedevelopment and occurrence ofcorticium in compost. Widespreadinfestations will result in yield reduc-tions of up to 10 to 20 percent, andreductions as high as 40 percent havebeen reported.

Corticium grows naturally as a commonrotter of cellulose (dead tree limbs,stored straw, etc.) and profusely sporu-lates when the weather is damp. It ispossible that spores of the Corticium-like fungi are carried by air currents intoa mushroom house before or during thespawning operation, or whenever thegrowing room is opened to the outsideenvironment. Improperly curedcompost is a good substrate for thismold. Yield reductions can be attributedto either the mold itself, poor compost,or the combination of the two condi-tions.

Vegetatively, an ink cap fungus producesa luxurious growth of white finemycelium in or on the compost beforeor after spawning. Round white pininitials the sizes of peppercorns (1⁄

16-inch

diameter) begin to develop on thecompost sometimes as early as 3 to 4days after spawning. Pins develop intomushrooms with narrow white stemsand scaly white to gray cone-shapedcaps. Once the mushroom forms(Figure 29), it disintegrates quickly intoink black liquid, giving this fungi itsname, ink caps. The black liquidcharacteristic of this genus is theproduct of autodigestion. Certain inkcap species develop a long fibrousrhizomorph (rootlike structure) thatextends into the compost.

Indicator Molds

Ink Cap Fungi

Common Names:ink caps, ink weed, wild mush-rooms

Scientific Names:Coprinus fimetarius, Coprinusradiatus, Coprinus sp.

Imperfect Stage:Ozonium, Rhacophyllus

Coprinus, or ink cap fungi, may appearduring spawn run or crop production.Ammonia seems to be a growth require-ment of this fungus, and impropermanagement of Phase I and IIcomposting, resulting in ammonia-typecompounds, is most often linked withthe appearance of ink cap fungi. It hasbeen suggested that variations in thefrequency of appearance from year toyear may reflect the abundance of inkcaps in the straw, cobs, or hay used incompost production, though this hasnever been proven. Ink cap populationsin such crops are probably influenced bycomposting and growing conditions.

Figure 29. After ink cap mushrooms mature, they disintegrate quickly into the ink-black liquid that gives the ink cap fungus itsname.

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Like Agaricus, the fruiting process ofCoprinus is cyclical, and ink capmushrooms occasionally may reappearin flushes. More often though, ink capmushrooms appear only once duringthe growing process. Once ammoniacompounds in the compost are gone,the compost pH decreases, and there isa gradual disappearance of ink caps.Mushroom spawn then will graduallycolonize the previously infested com-post.

Several species of Coprinus occur withthe mushroom crop. The larger ink cap,Coprinus fimetarius, is characterized by athick hollow stem and a grayish scalycap. This mushroom often is associatedwith severe substrate preparationproblems, either during Phase I or PhaseII. The smaller species, Coprinusradiatus, has a shorter thinner stem anda very fragile pale brown to yellowbrown cap. This mushroom often isassociated with a breakdown in supple-ments added at spawning time or aminor composting problem thatresulted in ammonia-type compoundsbeing released by the supplement. OtherCoprinus species have been isolated frommushroom compost, and unnamedspecies have been reported.

Ink caps may begin to grow as early asthe end of Phase II, but more often theyfirst appear during spawn run, aftercasing, or just before first break.Epidemic infestation of Coprinus oftenis associated with a difficult or poorlymanaged Phase II composting. Toomuch breakdown of raw materialsduring Phase I composting, whichaffects resiliency or conditioning of thecompost, or the addition of too muchwater, may contribute to a difficultPhase II and residual ammonia com-pounds. The addition of excessiveamounts of inorganic nitrogen tosubstrate causes an imbalance, whichalso can result in residual ammonia at

spawning time. The thermophilicmicroflora that grow during Phase II areunable to convert all the ammonia intomicrobial protein, and the microbes willuse up the available carbohydrate orwater before the ammonia has beencompletely converted. These ammonia-type compounds left in the substrateprovide food for ink cap development.Spotty or confined occurrences of inkcaps in parts of the room suggest thatthese areas contain compost that ispacked nonuniformly or too tightlyduring the filling operation. Highpopulations of nematodes have beenobserved in these areas of ink caps,further suggesting that a compacted,tight, or wet substrate was unable toproperly heat during pasteurization andthe remaining part of Phase II.

Compost moisture may favor thedevelopment of ink caps. Overly wetcompost is more difficult to condition,partially because of the reduced aerationwithin the substrate. Excessive use ofsteam, or steam used to maintain airtemperatures during Phase II, when toomuch fresh air is brought into the room,will cause condensation on the surfaceof the compost. Excessive condensationwill interfere with air and gas exchangefrom the compost into the air duringPhase II. Conversely, dry compost atfilling, or excessively high temperaturesor ventilation throughout Phase II, willresult in moisture becoming thelimiting factor for microbial growth.Therefore, the microbes will die beforethey are able to completely condition orconvert ammonia into microbialprotein. The resulting ammonia-typecompounds provide a food source forgrowing ink caps.

Ink caps also may grow as the result ofimproper temperature managementduring Phase II. Areas of the compost inwhich the compost temperature did notremain within the range of 115 to

140°F (46 to 60°C) from 72 to 96hours before and after pasteurizationmay contain residual ammonia. Oppo-sitely, composts that reheat (recycle) aslittle as 3 to 5°F (-16 to -15°C) nearthe end of Phase II will have additionalammonia produced via microbialammonification of nitrogen com-pounds. Rejuvenated microbes will usepreviously formed protein compoundsto obtain carbohydrates for their energy,and the nitrogen left from the usedproteins may be ammonified. A low airtemperature, cooler than 100°F (38°C)and maintained to manage the internalcompost temperature, can result in anammonia-laden layer (0.5 to 1 inch indepth) at the compost surface. In suchinstances, ink caps can flourish on theammonia remaining in this surfacelayer.

Locating the origin of ink caps can aidin deciding why the compost supportsink cap growth. A few scattered ink capsare little cause for concern and mayindicate compost nitrogen content atfilling time near the limit for a farm.However, a bountiful flush of ink capssuggests excessive ammonia atspawnings and is evidence that certainaspects of Phase I or Phase IIcomposting need to be corrected.

Plaster Molds and Flour Molds

Common Names:white plaster mold, brownplaster mold, and flour mold

Scientific Names:Scopulariopsis fimicola,Botryotrichum piluliferum,Papulaspora byssina, Thielaviathermophila, Sporotrichum sp.,Trichothecium roseum

Outdated Names:Monilia fimicola, Oospoio sp.,Myriococcum praecox

Perfect Stages:Dichotomyces (S. fimicola),Chaetomium (B. piliiliforum),Corticium (Sporotrichum), andHypomyces (T. roseum)

Imperfect Stages:Acremonium, Chrysosporium,Myceliopthora, Sepedonium,Sporotrichum, Thielavia

Although the fungus that causes flourmold is not the same as that causingplaster mold, it is generally believed thatthe same nutritional factors favor thegrowth of the two mold groups; so theywill be discussed together. Several fungihave been associated with the white andbrown plaster mold condition. Briefly,Scopulariopsis fimicola probably is themost familiar, and Botryotrichumpiluliferum is the most recently recog-nized. Species of Sporotrichum, Thielaviathermophila, and Trichothecium roseumhave been called plaster or flour molds.Brown plaster mold has been used todescribe infestations of Papulasporabyssina, Scopulariopsis fimicola, and P.byssina. The reader is referred to otherreferences to obtain more details on thetaxonomy of these fungi.

White plaster mold first appears, nearthe end of Phase II or during spawnrun, as a small irregular patch of whitespawnlike aerial growth on the compostsurface (Figure 30). Within a few days,this aerial hyphae begins to resembleplaster of paris. Eventually, the aerialgrowth completely disappears, leaves awhite mold on the compost surface, andlooks like spilled plaster or flour. Insome cases, the white plaster moldgrows from the infested area of thecompost and looks to be flecks ofplaster or flour on the casing surface.Some colonies have a pearly glisten, andthe mycelium is creamy white to buffcolored instead of snow white. Otherplaster or flour molds, species ofSporotrichum and Trichothecium roseum,appear initially as fluffy white moldsthat develop a light peach color andlight rose-pink color, respectively.

Thielavia thermophilia is thermophilic(heat loving), and for this reason isunique among indicator molds.Thielavia grows rapidly and abundantlyduring the last days of Phase II, and isfirst observed as circular- to oval-shapedpatches of fluffy white mold, 1 or 2 feetin diameter, on the compost surface.Before spawning, spores in the colonycenter start to mature, and the fluffytexture of the mold takes on a granular,flourlike appearance. Color changesfrom white to salmon pink and then tobeige. A few days after spawning, thewhite fluffy growth of this mold againmay appear salmon pink to beige-colored. The colonies may grow denselyand rapidly through the compost,eventually colonizing in large areas or inmany areas within the room. Thepowdery masses of spores becomeairborne when the infested area is

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Figure 30. White plaster mold first appears as a small irregular patch of whitespawnlike aerial growth on the compost surface.

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disturbed. Near the end of the cropcycle, areas infested by this mold usuallycontain numerous small black sphericalfruiting structures in addition to thefluffy beige form. These fruiting bodiesare the sexual stage of T. thermophila.Growth of this mold in compost occursin conditions similar to those that favorthe growth of other brown molds andink caps. It is possible that if compostconditions are conducive to the growthof one of these molds, several types orspecies may be growing in close proxim-ity to each other.

The rapid growth of T. themophila ininfested areas may increase composttemperatures to a range as high as 105to 120°F (41 to 49°C) and prohibit orkill spawn growth. Once the mold hasused up its food, the compost cools, andspawn often recolonizes the infestedareas if ammonification of the composthas not occurred. However, these areasoften fail to support either a vigorousspawn growth or high yields. This whitemold develops in restricted spots andhas not been observed infesting anentire tray or bed of compost. Conse-quently, high compost temperatures areencountered only in these spots, androutine monitoring of compost tem-peratures during spawn run may notreveal the presence of “hot spots” causedby T. thermophila. Presence of thisplaster mold is noticed most oftenduring a visual inspection of spawngrowth development. It may be detectedon farms where compost temperature ismonitored in a great number oflocations daily. Most other plaster andflour molds that occur in mushroomcompost do not cause “hot spots.”

The brown plaster mold fungus,Papulaspora byssina, first appears on thecompost surface during the spawn run.Dense plasterlike white mold maydevelop in areas 6 to 15 inches indiameter. As the fungus matures, thecenter of the colony changes from white

to yellow or tan, and then to brown,orange, or rust color. Brown plastermold colonies grow a bit above thecompost and often are outlined by anactively growing outer fringe of whitemycelium. Colonies tend not to befluffy in structure. Several colonies cangrow together to form a continuouscoating over the surface of the compostor on damp bedboards. After casing, themold may grow up through the casingand emerge on the surface. The moldusually is white at first, and the colormay change to the typical brown with awhite fringe. These molds are easilyrecognized by hand lens as a mass ofdarkly pigmented spherical structureson the compost straws or casing. Thebeadlike structures, called “bulbils,”appear and are interwoven with a finenetwork of white hyphae.

It is currently thought that growth ofplaster molds and flour molds occurswhere compost is too broken down oroverly wet during Phase I compostingand/or inadequately or improperlymanaged during the Phase II process.These molds develop in mushroomcompost when nitrogen sources, formedduring Phase I, are left after Phase II.These nitrogen-type compounds are notconverted into microbial protein, arereferred to as amines and amides, andmost often appear in composts with pHlevels above 8.5.

Long composting time, which results inoverly composted manure, is more aptto support the growth of these plasterand flour molds. Plaster or flour moldswill appear in a facility when improperlyconditioned compost is made. Althoughthe spawn will grow, conditions thatsupport widespread growth of plaster orflour molds will not support maximumyields of mushrooms. Modification ofcomposting practices to improvecompost quality usually reduces theoccurrence of flour and plaster molds.

Olive Green Mold

Common Names:olive green mold

Scientific Names:Chaetomium globosum,Chaetomium oliveaceum

Imperfect Stages:Botryotrichum, Humicola,Papulaspora, Scopulariopsis,Thermomyces, Trichocladium

Spores of the olive green mold fungusare heat tolerant and may survive at140°F (60°C) for 6 hours. However,this mold appears in compost wherePhase II ventilation is inadequate.Improperly managed Phase II aerationthat leads to an inadequate oxygen leveland compost temperatures greater than142°F (61°C) seems to promote theformation of compounds that appeartoxic to spawn growth but favor growthof olive green mold.

An inconspicuous grayish-white finemycelium growing in compost, or a finefluffy aerial growth on the compostsurface several days after spawning arethe early signs of this fungus (Figure31). Spawn growth is often slowed andreduced during the early part of thespawn growing period. Later in spawnrun, this mold’s fruiting structures maylook like very small gray-green cockle-burs or peppercorns about 1⁄

16 inch in

diameter. Fruiting structures are mostlikely to develop on straws in isolatedspots in the affected compost. Compostmay have a musty odor and often doesnot support mushroom spawn growth;therefore, it is common to see olivegreen mold in black compost that is notcolonized by mushroom spawn. Thefluffy white-grayish growth or greenfurry burs characteristic of olive greenmold are obvious even on compostcolonized by mushroom spawn.

Characteristically, burs are olive green ininfested compost, in contrast to theblue-green spore masses of Penicilliummold, or the forest-green Trichodermamolds.

Once it has been formed in the com-post, olive green mold persists through-out a crop. Spawn usually grows intoareas occupied by Chaetomium, al-though spawn growth often is delayed.Compost conditions conducive to awidespread infestation of olive greenmold may reduce spawn growthsignificantly, with a coincident reduc-tion in mushroom yields.

Compost that has a good structure, suchas that which is resilient when com-pressed or not overly decomposedduring Phase I, will allow for betteraeration during Phase II. Adequate airexchange throughout the entire Phase IIis necessary to prevent compost frombecoming anaerobic. Even a few hours

Black Whisker Mold

Common Names:black or gray whisker mold,whisker mold

Scientific Names:Doratomyces microsporus,Doratomyces stemonitis,Doratomyces purpureofuscus,Trichusus spiralus

Outdated Names:Stysanus stemonitis

Perfect Stages:Periconia and Cephalotrichum

Black whisker mold may occur incompost during spawn run or aftercasing. It first appears in spawnedcompost as an erect, black, whiskerlikestructure. The distinctive black whiskerappearance develops as the spores arematuring (Figure 32).

Black whisker mold fungus in compostindicates an unbalanced nutritional basein the compost at spawning time. WhenChaetomium green mold is present,black whisker mold also will be present,since both are celluolytic, or fungi thatfeed on cellulose.

Black whisker mold grows rapidlythrough the compost at the end ofPhase II and at the beginning of thespawn run. Heavily infested areas ofcompost appear darker than usualbecause of the masses of black powderyspores. When disturbed, these spores areliberated and the compost appears to be“smoking.”

Black whisker mold is not thought to bea serious competitor of mushroomspawn. Its presence usually indicatesthat the straw has been incompletelydecomposed or caramelized. Low Phase

of too little air sometimes is enough tocause compost to become anaerobic andconducive to olive green mold growth.The proportion of outside air intro-duced into a room to ensure aerobicconditions in the compost throughoutPhase II varies from facility to facility.

Excessive compaction or oversaturationof compost with water at filling timeshould be avoided. Proper manipulationof steam valves, fresh air dampers,doors, and high-speed exhaust or intakefans can ensure the availability ofenough air to the compost during PhaseII. These procedures also enhanceaerobic thermogenesis in the compost,which enables compost temperatures toremain hotter than the air temperatureduring Phase II. Air temperature and airvolume should be managed to maintaina temperature differential and gasexchange between the compost and theair.

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Figure 31. Early signs of olive green mold are an inconspicuous grayish-whitefine mycelium growing in compost, or a fine fluffy aerial growth on the compostsurface several days after spawning.

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I temperatures result in excess carbohy-drates that are easily used by blackwhisker mold. Black whisker mold alsomay indicate that nitrogen supplemen-tation of fresh compost ingredients wasinadequate, or conversely, that theproportion of carbohydrates was toohigh. It has been reported that thismold also grows in compost thatoverheated during spawn run.

Whether spores of black whisker moldsurvive peak heat is not known. Growthof Aspergillus and Penicillium molds alsoare favored by conditions conducive tothe growth of black whisker mold, andthese fungi also may be present in thecompost. Black whisker mold, Aspergil-lus, and Penicillium are mold fungi,which produce abundant numbers ofspores. Air heavily laden with spores

from these fungi, often erroneouslycalled “gas,” can induce an acute allergy-type response in dumping crew person-nel. Workers may report respiratorytroubles often characterized byasthmalike symptoms including nasal orthroat irritation, chest congestion,breathing difficulty, nosebleed, oralternating fever and chills. Theresponse is transitory, but a personsensitive to these spores becomes moresensitive with each exposure, and thediscomfort may become more intense.Sensitive or sensitized workers should beassigned tasks elsewhere, away fromcompost dumping. Proper preparationof compost precludes the developmentof these molds, so these molds areunknown at many facilities.

Smoky Mold

Common Name:smoky mold

Scientific Name:Aspergillus spp.; Penicillium spp.;Penicillium chermesinum

Several species of Penicillium have beenreported in mushroom compost, andmost are harmless to the spawn andoverall yield; yet, it recently has beenreported that P. chermesinum has causedserious crop losses when introduced intoPhase II compost at spawning time.Symptoms begin to show up as edgebreaks at first break. Digging intoinfested areas causes large clouds ofspores to form; hence the name “smokymold.” Aspergillus and Penicillium oftenare greenish in color, whereas P.chermesinum is characteristically whiteat first, then turns brown. All smellmoldy.

Reported incidence of P. chermesinumoccurs mostly in bulk Phase I and IIsystems. Other smoky molds can befound in all systems. It has beensuggested that P. chermesinum hasoriginated from dirty straw and fromother Penicillium spp. and Aspergillus inoverheated, supplemented compost afterspawning. A large P. chermesinum sporeload infecting compost at spawning hasthe most devastating effect on yield.Much like Trichoderma green mold,there may be an interaction between themycelium of this mold and Agaricus. Ithas been suggested that spawn is eitherparasitized or effectively repressed insmoky mold. Control of this particularmold is similar to virus control; there-fore, extreme hygiene and sporeexclusion is essential. However, thespores are quite small, so HEPA filtersare required to remove these two-micron spores. Cleaning before andafter spawning is essential.

Figure 32. Black whisker mold first appears in spawned compost as erect blackwhiskerlike structures, highly magnified in this photo. The descriptive blackwhisker appearance develops as the spores mature.

(No slide)

Other smoky molds often are found incompost where less protected spawningsupplements are present and overheatduring spawn run or after casing. Evenbrief periods of temperatures above90°F (32°C) can damage or kill thespawn. These Penicillium and Aspergillusmolds easily colonize the dead spawngrains and supplements. Compost inthese areas is generally black at casing orsometimes has a mosaic appearance.Often, these black areas appear towardthe center of the beds, where tempera-tures are warmer (Figure 33). If theoverheating occurs within 2–3 days afterspawning, residual bacteria may causecompost to begin heating. Often,compost may smell clear of ammonia at

spawning, but it will not be completelyconditioned. These residual compoundsprovide food to the bacteria or othermesophilic (heat-loving) microbes.Control of these molds is ensured bycompost, which is maintained in theconditioning range during Phase II untilit is completely conditioned. It is alsoimportant that enough, but not toomuch, moisture is in the compost. Drycompost may result in the microbesrunning out of water before they havecompletely used all the availablenitrogen. Conversely, wet compostprevents proper aeration within thecompost and prevents the microbesfrom growing.

Oedocephalum Mold

Common Name:brown mold

Scientific Names:Oedocephalum sp., Oedocephalumfimetarium

Brown mold may appear occasionally asearly as during cooldown, beforespawning, but more often developsduring the latter part of spawn run. Themold first forms irregularly as a lightgray mold growing on the compostsurface; but within a few days, sporesform and begin to mature, and the colorchanges to dark tan, fawn, or lightbrown. The growth habit ofOedocephalum brown mold varies froma weak growth over the compost surfaceto a dense coating on the compoststraws. This mold grows on compostmost of the time, but occasionally it isseen after casing. After casing,Oedocephalum grows slowly from sites ofinfestation up through the casing andmay appear on the casing surface beforepin formation. The pearly-whitemycelium of Oedocephalum growsloosely over the surface, but its colorchanges to silvery brown as the fungusages and the spores mature (Figure 34).

The appearance of this fungus, discern-ible through a hand lens, consists of anerect spore-bearing structure with aglobular cluster of large spores at its topend. Rubbing Oedocephalum brownmold between the thumb and indexfinger produces a gritty sensation similarto that experienced in rubbing finesand. This gritty characteristic distin-guishes Oedocephalum sp. from otherwhite-brown molds in mushroomcompost or on casing. Spores ofOedocephalum sp. are common in mostmushroom composts, but they liedormant unless induced to germinate

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Figure 33. Compost in smoky mold-infected areas is generally black at casing, orsometimes has a mosaic appearance. These black areas often appear towardthe center of the beds, where temperatures are warmer.

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Figure 34. The pearly white Oedocephalum mycelium, discernible through a hand lens, consists of an erect spore-bearingstructure with a globular cluster of large spores at its top end. Its color changes to silvery brown as the fungus ages and thespores mature.

and grow. The environmental andnutritional conditions that encouragegrowth are not fully understood.Usually, Oedocephalum brown moldgrowing in compost indicates thatammonia and amines were not com-pletely eliminated during Phase II andare serving as a food for this organism.Growth of Oedocephalum does notinhibit spawn growth, but conditionsfavoring its growth are not optimal formushroom production. Compostconditions similar to those described forplaster molds are associated with thegrowth of Oedocephalum brown mold.

Bacterial Blotch—Pseudomonas tolaasii

Description

Pseudomonas tolaasii, the cause ofbacterial blotch, is an aerobic, non-spore-forming fluorescent bacterium inthe genus Pseudomonadaceae. It is acommon bacterium; many fluorescentPseudomonads are readily isolated fromfield soil. These groups of bacteria arerather closely related and often difficultto distinguish, although a uniquefeature of the species P. tolaasii is itsability to infect and discolor commercialbutton mushrooms. The discoloration ispale yellow at the start and darkens to agolden yellow or rich brown color. Theblemishes are superficial but decreasethe eye-appeal of mushrooms and lowertheir quality in the marketplace. Thisbacterium is not a threat to humanhealth.

Control

Managing bacterial blotch disease onmushrooms is a matter of chlorinatingthe irrigation water applied to the cropto a concentration of 150 ppm chlorine;using water that is potable (drinkable)as a source for irrigation water; andmost importantly, inducing the caps ofthe mushrooms to dry after an applica-tion of irrigation water. It is common toinclude a 2- to 3-hour drying cycle inenvironmental management afterirrigation. During this time, the

ambient temperature should be raised afew degrees, the humidity should belowered to below 85 percent, and thetotal airflow should remain unchangedor increased by 10–15 percent. The goalis to lower the humidity in the growingroom to induce the mushrooms to dry.

Experience suggests that when themushroom compost is too dry when itis spawned—less than 60 percentH

2O—the above steps will not elimi-

nate bacterial blotch from the crop.Also, when the source of the peat mossused to case the mushroom beds haschanged, bacterial blotch may not becontrolled, because some peats foster P.tolaasii more than other peats. Anotherenvironmental situation in whichbacterial blotch is almost impossible tocontrol is when the external air tem-peratures are moderate (59 to 72°F, or15 to 22°C) both day and night, andthe air is full of water vapor. In such asituation, the condenser of the airconditioner does not turn on, since theair temperature in a growing room iswhat the grower specified. Since themushroom growing temperaturerequirement has been satisfied, themoisture in the outside air is notcondensed on the cooling coils. In suchinstances, placing an electric light closeto the air temperature sensor will causethe control system to register that theincoming air is too warm. The con-denser will begin to operate, which willremove some of the excessive water fromthe incoming, ambient air.

C. Pest Species Biology and Control

4. BacterialDiseases

Paul Wuest

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Strain Choice

There are a few reports that some wildspecies of Agaricus bisporus possessresistance to bacterial blotch. Inaddition, there are differing levels ofsusceptibility among the commercialstrains of hybrid white and hybrid off-white mushrooms. Growers may be wiseto try different strains to determineresponse to bacterial blotch, selectingthe strain that performs best in theoverall conditions at the facility.However, choosing a strain of A.bisporus based exclusively on its suscep-tibility to bacterial blotch may not be inthe best interests of production at afacility. Managing bacterial blotch is notsimple, and sometimes the best effortsfail. This approach allows a producer tochoose a strain well suited for theunique environmental conditions ateach facility.

Mummy and FalseMummy—Pseudomonasspecies

Description

Mummy disease is characterized bymushrooms that develop to the buttonstage or larger, then stop growing. Theaffected mushrooms sometimes developa curved stipe with translucent, longitu-dinal streaks on the inside. The mush-room tissue becomes mummylike inappearance: spongy, dry, and leathery.With an early onset of mummy disease,first-break mushrooms will be delayedin their development by a few days, buta break of mushrooms does develop andcan be harvested. Second-break mush-rooms in the same location exhibit thefull-blown symptoms of mummydisease. Thereafter, mushrooms nolonger will grow in that area. The poorquality of the mushrooms and the lackof subsequent harvest from infectedareas can create a severe economic loss.

The causative agent that inducesmummy disease is a bacterium, a speciesof Pseudomonas closely related to butnot the same as the bacterium thatcauses bacterial blotch. ManyPseudomonas bacteria commonly arefound in and on organic matter, so it isdoubtful the mummy bacterium is aunique organism introduced fromoutside a mushroom farm. Rather, themummy bacterium may be a normalpart of the bacterial microflora of mostmushroom composts. When conditionsfavor its growth and reproduction, itspopulation grows large enough to causethe disease recognized as mummy.

A scientist working at a cave farm inMissouri in the 1930s first describedmummy disease. It appeared as areasonably large patch of mummifiedmushrooms on first break, with the size

of the affected area getting larger as thecrop aged from break to break. Thissymptom pattern continued until themiddle 1970s, when off-white strainspredominated at mushroom farms, andinto the 1980s, when hybrid white andhybrid off-white mushroom strains werethe most widely grown strains of A.bisporus at mushroom farms. Since then,mummy disease seems to initially affecta few squares (8 to 12 lineal feet) in agrowing room at traditional bed farmsand does not spread along a bed after itfirst appears. This newer expression ofmummy disease, sometimes referred toas false mummy, shows additionalsymptoms. These include a fuzzymycelial growth at the base of mush-rooms (Figure 35) and very coarsestrands (rhizomorphs) attached to themushrooms when picked. Also, a layerof tissue at the base of the stipe turnsmahogany brown or yellow-brownwhen the stipe is cut longitudinally andexposed to the air for a few minutes.The bed area affected by these newersymptoms increases very little in sizefrom break to break. If the symptomaticarea is allowed to dry between breaks,some mushrooms will grow and can beharvested from the affected areas.

An unusual phenomenon has been seenrepeatedly when mummy diseaseappears in a growing room. It isreasonably common for the totalproduction from the room withmummy disease to be equal to orgreater than the production from aroom where no mummy disease occurs.This oft-repeated observation suggeststhe bacterium associated with mummydisease may be ecologically related toone or more other organisms that arecapable of enhancing production. Or,the conditions that favor mummydisease development also favor theoptimum production of mushrooms.

At farms when spawned compost iscovered with plastic for the spawn runperiod, some growers have seen lessmummy disease when they cut openand turn back the plastic wheneverwater accumulates on its underside.This practice prevents the accumulatedwater from dripping into the compostand soaking the top of the bed.

In the 1970s, when off-white strainspredominated, it was common practiceto remove the plastic a few days beforecasing to ensure the surface of thecompost was completely dry beforecasing was applied. The off-white strainswere much more sensitive than earlierstrains and could be harmed by toomuch water in/on the surface compost,unrelated to the mummy threat.Mummy misdiagnoses often occurredwhen compost beds were cased whenthey were too wet. Under these condi-tions, spawn growth into the casing wasslow, mushroom formation was delayed,and the mushrooms appeared to havethe characteristics of mummy disease. Infact, the problem was water stress, notmummy disease.

Control

The effectiveness of mummy controlmeasures may be difficult to predict,though moisture management is thebasis for many control efforts. Experi-ence suggests that during times of theyear when evaporation from spawnedcompost or cased mushroom compost isless than it should be, mummy diseasedevelops. Bed growers in ChesterCounty, Pennsylvania, have hadexperiences in which the addition ofwater to compost before or at the timeof spawning predisposed the compost tosupporting mummy disease. Oddlythough, bed growers in Berks County,Pennsylvania, added water to compostat spawning without this response.Other factors may be involved: BerksCounty growers generally used morehay in blended composts, while ChesterCounty growers use more horse manureor straw in their blended composts.

Figure 35. Mummy disease, showing the tilted cap and fuzzy bottom stems. Another attempt at mummy controlwas to water the surface of the compostwith chlorinated water (150 ppm Cl) afew days before casing. Some growerswere confident this practice controlledmummy; an equal or higher numberassumed it enhanced the amount ofmummy in a crop.

Sanitation and hygiene cannot beoverlooked in efforts to control mummydisease. In their absence, mummy-infested compost moving through a trayline can contaminate the equipment,which in turn contaminates the com-post moving along behind it. Onemummy-infested tray of compost canserve as an inoculum source and infestmost of the other compost in onegrowing room of trays. At tray farms,especially, mummy disease can causedevastating crop losses. Thoroughwashing and sanitizing of tray-handlingequipment is essential to minimize thethreat of spreading the cause of mummydisease; the same is true for spawningequipment. Special attention to sanita-tion and good hygiene in and aroundspawn bags, spawn, and the spawningprocess is essential.

Sanitation and hygiene, practicedwithin an environment where moisturemanagement promotes evaporationfrom compost and casing, are the onlyways to reduce the threat of a mummydisease infestation.

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Introduction

Nematodes thrive in raw compost andcan exist in excessive numbers duringthe mushroom growing process. Whilesome growers believe that nematodes aremerely an indicator that compost andcasing preparation has gone awry, it iswiser for growers to assume thatnematodes can represent the risk ofyield losses, and to take precautionsagainst their proliferation.

Nematodes

Nematodes are tiny, very primitiveroundworms. They appeared early onthe evolutionary stage, being the firstanimals to evolve a body cavity. Theyare extremely abundant in both typesand numbers. There are about 12,000species currently known, but scientificopinion holds that the number ofspecies actually could be 100 timesgreater. Typically, nematodes range insize from 0.2 mm to 6 mm in length,though some may be much longer.

Nematodes are found in marine,freshwater, and soil habitats. It has beenestimated that there are 8 billionnematodes in an average acre of fieldsoil. One square meter of garden soilprobably contains approximately 2 to 4million nematodes. Many are parasites;in fact, almost all types of creaturesstudied by scientists have at least onespecies of nematode that parasitizesthem. Roughly 50 species parasitizehumans.

Caenorhabditis elegans, one of thesaprophytic nematodes to be discussedbelow, has become an important toolfor genetic and developmental research-ers. This organism is made up of only1,000 cells. It matures in 3 days and hasa transparent body that allows scientiststo watch the dividing cells.

C. Pest Species Biology and Control

5. Nematodes

Phillip S. Coles

Nematodes in MushroomGrowing

It is fortunate that nematodes do noharm in raw compost, because they areubiquitous in the materials used toprepare the compost mix, and theircomplete removal, if possible, would beextraordinarily expensive. The richnessof the compost environment in terms offood, water, and oxygen providesnematodes with an excellent habitat, atleast until composting temperaturesreach lethal ranges. The cooler outerportions of the rick, if not mixed andturned into the interior, will continue tosupport nematode populations intoPhase II.

There are four general types of nema-todes: parasitic, saprophytic, predatory,and animal parasitic. Only the first twoare discussed here. For mushroomgrowers, the primary difference betweenthese two groups lies in their feedinghabits. The parasitic nematode feedsdirectly on mushroom mycelium,whereas the saprophytic nematode feedson bacteria, protozoa, fungal spores, andother bits of organic matter, but doesnot attack the mycelium.

Parasitic Nematodes

These nematodes, also referred to asfungal-feeding or mycophytic nema-todes, are increasingly rare in mush-room farming today. Presently, industrychoices of casing materials or pasteuriza-tion of casing usually avoid outbreaks.In the past, however, they were respon-sible for disastrous crop losses.

The parasitic nematodes use their stylet(a needlelike mouthpart) to pierce themycelial cell and inject digestive juices.The same stylet then becomes strawthrough which the nematode consumesthe liquefied cell contents. As nema-todes move through the mycelium-filledcompost, they first destroy the finehyphal structures and leave the myce-lium looking stringy. Thereafter, largermycelium is destroyed, leaving smallbarren bed areas that grow progressivelylarger as the nematodes venture outwardinto healthy compost. If the conditionsare optimal for the nematodes—moderate temperature (68–77°F, 20–25°C) and wetness—entire beds can bedenuded of their mycelium. Dependingon the number of nematodes on thebed, the mushroom crop will bereduced or eliminated.

Under good conditions, nematodes canmultiply 30- to 100-fold in 2 weeks.When their burgeoning populationexhausts the compost of its nutrients,the nematodes respond to the changingenvironment by swarming to thesurface. Exposed there, they can bepicked up easily by vectors such ashumans and flies. If dried slowly, thenematodes become dormant and can bedistributed by even slight air move-ments.

Compost infested with nematodes has acharacteristic appearance: soggy, soursmelling, and depressed. The nematode-trapping gray mold, Arthrobotryssuperba, may appear in areas where themycelium has been destroyed. Thissoggy mess is apparently good habitatfor the saprophytic nematodes, thesecond of the two types discussed here,for they frequently appear in these areas.

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At low levels, these nematodes havelittle effect on mycelium. As thenematode numbers increase, myceliumbegins to grow slowly and weakly. Athigh infestation levels, the strandscompletely degenerate. Researchsuggests that the extent of thesaprophytic nematode damage tomycelium is closely tied to the numberof bacteria, the nematodes’ primaryfood source, present in the spawnedcompost or casing. Their detrimentaleffects on the mycelium appear to belinked to the release of a toxin orbyproduct into the compost. Extractstaken from diseased compost and casingshow there is greater crop damage whenboth bacteria and nematodes are presentin high numbers than when onlybacteria are present. The enhanced cropinjury may be the result of increasedproduction of toxins when both arepresent, or may reflect some way inwhich the nematodes make possible amore rapid or thorough bacterialcolonization of the compost.

There is an interesting ecologicalrelationship among the nematodes,bacteria, and mycelium. Under exces-sively wet compost conditions, bacteriahave an advantage over mycelium, andas the nematode food source, theirincrease in numbers encourages theexpansion of the nematode population.The high numbers of bacteria alsoinhibit normal growth of mycelium.The compost deteriorates and becomeswet and increasingly anaerobic. Underless wet conditions, the mycelium canspread, use the water for its owngrowth, and dry out the compost to apoint that inhibits the bacterial prolif-eration. The nematodes remain in lownumber because of the dry conditionsand the limited food source. Theenvironment remains favorable formushroom production.

Saprophytic Nematodes

These nematodes, often referred to as“free-living,” now are more commonlyassociated with mushroom farming thanthe parasitic species. They characterizepoorly prepared compost and/or casingand cause severe deterioration ofmycelium in their own right. Thecommon saprophytic species are listedbelow. In most cases of infestation, twospecies of these nematodes are present.

Common Saprophytic NematodeSpecies

Acrobeloides apliticus

Acrobeloides buetschii

Caenorhabditis elegans

Cruzenema lambdiensis

Panagrolalmus rigidus

Pelodera (Pelodera) strongyloides

Rhabditis (Cephaloboides) oxycera

Rhabditis (Choriorhabditis)longicaudatus

Rhabditis (Rhabditis) terricola

Rhabditis (Pellioditis) pellio

Saprophytic nematodes’ feeding habitsdiffer markedly from their parasiticcounterparts. They suck in and chewthe particles of food they consume.They possess a muscular pharyngealbulb, which creates the suction to drawin food particles and liquids. Thesaprophytic nematodes multiply evenfaster—one hundred-fold in 3 days—than those that are parasitic. Many ofthese nematodes are parthenogenetic(self-fertile).

Effects on mushrooms can range fromlittle damage to total elimination of thecrop. The appearance of the compostcan gives clues to the damage to come;when dark, watery, barren patchesdevelop, production will be severelyaffected.

Survival Characteristics

Nematodes owe their abundance andwidespread distribution in part to theirremarkable survival abilities. If driedslowly, they enter a heat-resistantdormant state that can persist for yearsuntil they contact enough moisture tobreak dormancy. In the dried state, theyare distributed easily by air currents.They also can survive without food formonths. They are not susceptible tocold or freezing, and they regain theirvigor once temperatures are moremoderate. When their high numbersbegin to deplete the readily availablefood supplies in compost, they show acollective swarming behavior that bringsthem to the compost surface for agreater chance of dispersal. Thesaprophytic nematodes take this groupbehavior a step further and form intocolumns of living nematodes, hundredsstrong, that wave about on the surfaceof the mushroom bed, ready to adhereto hands, tools, flies, or other objects.This phenomenon is called winking.The waving strands of winking nema-todes can be observed by holding aflashlight at a 45-degree angle to thebed. A grower’s IPM plan should takeinto account these survival traits tominimize the opportunities for nema-tode dispersal.

Sources of Inoculum

Nematodes are carried into the growingprocess in a number of ways; the mostobvious of which is in the compost. Asnoted above, nematodes are associatedwith raw materials entering the compostyard and respond by proliferating in theinitially favorable compost environ-ment. On the cooler parts of the rick,inside clumps of compost materials, orin excessively wet compost, they maysurvive Phase I and enter Phase II. Thevast majority of their population may bedestroyed in a Phase II room duringpasteurization at about 140°F (60°C),but survivors can persist in wet areas,dry areas, and clumps, and can continueon to spawning. There they encounter amore favorable environment: tempera-tures around 75°F (24°C), moistconditions, and near-neutral pH (7.5).Mixing at spawning distributes thenematodes. The spawning machine cancontaminate many subsequent beds ortrays after spawning a single infestedbatch of Phase II compost.

Peat, as it is introduced into thegrowing process, is dry, has a low pH,and usually does not contain nema-todes. Once in place as casing, however,as conditions become more moist, peatprovides a favorable environment.Compared to compost, casing providesa habitat with less interference bymycelium. Pasteurization temperatures,as noted above, and careful watering(moist but not wet) can reduce oreliminate nematode populations; butfailure to manage these environmentalconditions can allow nematodes tomove further into the growing process.

Another source of nematodes in a cropis a preceding infested crop. In growingrooms, woodwork and ceiling insulationcontaminated with nematodes caninoculate successive crops. If hightemperatures during pasteurization donot penetrate into the wood, especiallyinto the cracks and crevices, nematodeswill not be destroyed. Likewise, mois-ture dripping from contaminated ceilinginsulation spreads nematodes to newbeds.

Nematodes can invade growing roomsfrom other areas of production in avariety of ways. Dust can carry dormantnematodes between rooms, and flies,mites, hands, boots, and tools can carrynematodes acquired from contact withswarms or contaminated materials.Equipment such as spawning machines,if not designed for easy cleaning and ifnot routinely sanitized, provide nema-todes with an effective means ofdistribution.

Sampling, Separation, andIdentification

Ricks, trays, or beds that are suspectedof infestation can be tested for presenceand relative quantity of nematodes. Inany testing procedure, the integrity ofthe sample is critical; in this case, thelocation at which the sample is collectedcan strongly influence the results.Collecting samples from the hottestportions of the materials usually willgive negative results because nematodesrarely survive there. Sampling at coollocations or areas where heating hasbeen nonuniform in the past is morelikely to produce detection of the pests.Incubation of samples sometimes isnecessary to provide adult nematodesfor identification.

Nematodes can be separated fromcompost or casing and identifiedvisually. A Baermann funnel (Figure 36)is a convenient tool for collectingnematodes for further investigation. Theapparatus consists of a support systemthat holds a funnel with a bottom tapclosure. The funnel is filled with freshwater. A cloth or strong, fine mesh bagis suspended over the water at the top ofthe funnel. Strong commercial tissueswill work. A sample of compost orcasing is placed into the bag. Thenematodes move out of the sample, andsince they are slightly denser than water,sink down the funnel until they arestopped by the tap closure. The tapclosure is opened after the migration hasproceeded for several hours, and thenematodes are collected in a shallowglass dish.

Nematode identification by nonexpertsis limited to differentiation of generaltype or genus level. The most usefuldistinguishing characteristic is theappearance of the anterior (front) endwhere the mouthparts are located. A

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blunt end from which the needle-likestylet can extend shows the organism tobe parasitic. Saprophytic nematodeslack the stylet and appear to have liplikebulbs stuck on their anterior ends. Bynoting the structures of the anteriorend, the shape and size of the internalstructures, the body length and otherfeatures, and contrasting them topublished illustrations of nematodetypes (rhabditoid, aphelenchoid, etc.),the nematodes’ identity can be deter-

Control Measures

Because nematodes are ubiquitous, totalprevention of nematode invasion andtotal eradication during infestations isunlikely. Further, since nematicides arenot available to mushroom growers,measures to prevent or control infesta-tions are limited to ensuring thatnormal temperature and sanitationsafeguards are followed, and thatenhanced measures are instituted whennecessary. A well-prepared IPM pro-gram should outline clearly thesemeasures and help keep all members ofthe growing team on track.

The Phase I rick provides the growerwith his first opportunity for nematodecontrol. Good Phase I temperatures,uniform mixing of the raw materials,and ensuring that cool shoulders aremoved to the interior positions aremeasures that will reduce the number ofnematodes moving on to Phase II.

Compost should be pasteurized at140°F (60°C) for 2 hours to subject thenematodes to killing temperatures. Thistemperature range is adequate to killwet nematodes, but if the compost andnematodes dry out, temperatures ashigh as 160°F (71°C) would be requiredfor lethal effect. The compost mayrequire moisture adjustment to avoidbeing overly dry, but care should betaken not to make the compost soggy,or bacterial development will beencouraged. The heating system shouldbe checked and compost temperaturesmonitored to verify that uniform peakheats are reached in all areas of thecompost. Casing should be pasteurizedat 140°F (60°C) unless the grower isconfident that each shipment is free ofnematodes. Recontamination of thecasing should be avoided.

Figure 36. A Baermann funnel is a simple tool for extracting nematodes frommaterial.

mined well enough to make controljudgments or to process comparisons.But, for the grower, simply the existenceof nematodes, regardless of the species,is a problem.

At spawning, any compost suspected ofharboring significant nematode popula-tions should be processed last andfollowed by scrupulous cleanup ofmachinery. During cropping, thegrower can do little to control aninfestation other that to prevent furtherspread. One of a grower’s challenges isto rid the growing room of its legacy ofnematodes. Pasteurization at tempera-tures of 160°F (71°C) should beconducted.

Scrupulous attention to sanitationthroughout the growing process, thehallmark of a properly maintained farm,will contribute greatly to nematodecontrol. In addition to typical sanitationpractices, the following should beconsidered:

● Develop and enforce rules restrict-ing personnel movement betweencompost areas and growing rooms.

● If trays, shelf boards, or other suchitems cannot be pasteurized, theycan be washed with a steampressure washer—though thistreatment may be insufficient tokill all nematodes. Sanitizers shouldbe used in rooms and on equip-ment. This is especially importanton floors, since they act as a heatsink during pasteurization andrarely can have their temperaturesraised sufficiently to kill nema-todes.

● Redouble sanitation efforts atspawning. Review spawningmachine design and positioning todetermine if better cleaning ispossible with adjustments orretrofitting.

● Take precautions against nematodespread by bits of spilled compostfrom infested trays. Clean up anydropped materials before they arecarried into noninfested areas.

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Case History #1: Ross and Burden

(as presented in “An unusual problem—saprophagous nematodes.” Mushroom

News. January 1982.)

Ross and Burden describe sudden, massive crop losses that were traced

eventually to saprophytic nematode (Rhabditis) infestations. In the first occur-

rence, the farm’s production dropped 50% in two weeks, and in a later instance,

dropped to 10% of budgeted levels. Ross and Burden observed lost production

in the first break, with barren patches appearing on some trays. Other trays were

completely barren. Mycelial degeneration was evident, pinning was poor, and

large numbers of nematodes became visible.

Their investigations uncovered, among other things, that the production problem

was worse on trays that were watered at spawning, and that significant numbers

of nematodes were surviving peak heat. After further investigation, they con-

cluded that active compost (which also had a higher-than-normal initial load of

nematodes) required extra fresh air in Phase II. However, the air/bed temperature

differential was sufficient to dry and cool the surface of the compost, a condition

that protected the nematodes from heat kill. Flooding during the same period

likely had carried many nematodes into the farm, providing the unusually high

pest pressure. The coincidence of the extra burden of pests and the surface

drying in Phase II set off the chain of events that resulted in catastrophic infesta-

tion. They reported, “A few simple anti-nematode measures were put into

operation, and the farm yield recovered very quickly. . . .”

This incident and another nematode problem with a shelf operation provided the

investigators’ impetus to delve further into the factors influencing nematode

infestation. They concluded that saprophytic nematodes could be a primary

cause of crop losses.

These control measures should beused as the basis of a grower’s controlprogram, but in certain cases,infestations appear that requireremedies tailored to the particular

farm operation or even the season of theyear. The two case histories belowillustrate creative problem solving innematode control.

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Case History #2: Barber and Cantarera

(as presented in “Seasonal nematode problems.” Mushroom News. June 1987.)

Barber and Cantarera described a common phenomenon, occurring in late

winter and spring in southeastern Pennsylvania, of dramatic increases in

nematode populations in crops ready to pin. They suggested a cause and

described measures to remedy the problem.

The phenomenon, they wrote, has its origin in the cold shoulders found in

compost ricks during the winter months. If effective cross-mixing of the rick is

not accomplished, these regions fail to achieve the temperatures necessary for

nematode kill. This extra load of nematodes is carried into Phase II, where routine

pasteurization practices may be unable to bring nematode populations down to

safe levels. Barber and Cantarera suggest that sampling of Phase II trays in

locations likely to be cooler (near sideboards, ends, and surfaces) gives a better

indication of nematode survival than sampling the centers of trays. When

swarming of nematodes is observed before pinning or by first break, the grower

can safely assume that Phase II pasteurization has fallen short of expectations.

Dryness may be the cause, and moistening the compost surface at fill or just

before pasteurization assists the normal peak heats in producing the necessary

kill. However, the wetting must be judicious and soaking avoided. These simple

measures have mitigated seasonal nematode problems. They warn farmers to

avoid the belief that nematodes are “not really harmful.”

The Future

The future may hold new options fornematode control. At the present, wehave few ways of dealing with nema-todes once they are infesting a bed. Butnew applications of biological controlmay change that. Nematode-trappingfungi, for example, hold promise forpest control. These fungi can pierce theouter surface (cuticle) of nematodes,invade their bodies, and lay spores onthe inside. In the process, the nematodeis killed, but before death comes, itsmovements can disperse the fungi by

carrying spores through the compost orcasing. Research has shown thatArthrobotrys irregularis kills nematodes,but use of this fungus has not developeda wide following.

A great aid to the grower would be thedevelopment of strains resistant to thetoxins that are suspected of beingproduced in nematode infestations. Off-white and white strains were shownyears ago to react differently to extractsprepared from nematode-infestedcompost and casing, giving rise to hopesfor commercially effective levels ofresistance in the hybrid mushroomstrains used today. Unfortunately, such

strains are not available yet, but theirpursuit is a worthwhile venture forresearchers.

Conclusion

This section could not end with a bettermessage than that contained in the lastsentence of Case History #2. A compla-cent opinion that will not serve thegrower well is that nematodes, especiallysaprophytic nematodes, are not reallypests, or that they are only indicators ofother problems. A valid IPM programmust consider the potential for nema-tode infestation and detail all farm-specific anti-nematode measures toavoid expensive crop loss, especiallysince pesticides are not an option.

Introduction

Of all the diseases confronting thegrower, none has been the subject ofmore confusion than virus disease. Ithas been known by a variety of names,shows a wide range of symptoms, and inthe early stages, can be overlookedcompletely. Virus disease can beconfused with the effect of poor culturalpractice. It is increasingly apparent,though, that the economic impact ofvirus disease is significant and realizedworldwide.

History of Virus Disease

Virus disease, which also is known as LaFrance disease, dieback, X disease,watery stipe, and brown disease, wasnoted first in 1948 by James Sinden andEdith Hauser on the La France Brothersmushroom farm located in southeasternPennsylvania. The disease was reportedlater in England and the Netherlands,and probably occurs worldwide.

We now are confident that La Francedisease is caused by a virus. During the1960s, Michael Hollings in Englandproposed that a virus caused thisdisease. He prepared extracts fromdiseased mushrooms and found thatthey contained several types of viruslikeparticles when viewed at a high magnifi-cation with an electron microscope.

The scientific confirmation of the viralcause of the disease did not come easilyor quickly. Only after many years ofscientific research was the identity ofthese viruslike particles determined withsome certainty. It is now known thatthere are at least three types of viruses ofinterest to mushroom growers. LaFrance isometric virus (LIV) is thoughtto be the main cause of virus disease.Mushroom bacilliform virus (MBV) isassociated with the disease, but may be abenign virus. Vesicle virus (VV) alsoappears to be a benign virus that iswidely distributed in commercialmushrooms.

C. Pest Species Biology and Control

6. Virus Disease

C. Peter Romaine

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Disease Symptoms

Part of the confusion surrounding virusdisease likely resulted from the range ofsymptoms by which the disease presentsitself. The disease can reveal itself in twoseverity ranges. In its less severe form,the virus causes only minor yield losses.Mushrooms have a normal appearance,although yield may be slightly de-pressed, and the crop appears to besuffering the effect of poor culturalpractices.

In the more severe form, the diseasecauses a delay in the emergence ofmushrooms. When the mushroomsappear, they have small caps and longstems that growers refer to as the“drumstick syndrome” (Figure 37). Themushrooms may look similar to thosegrown in an atmosphere with an

elevated level of CO2. The mushrooms

are poorly anchored in the casing, andtheir veils open prematurely anddischarge spores. Nematodes andlipstick mold may be abundant in thecompost, indicating inadequate andnonuniform peak heats in Phase I andPhase II. In many cases of severe virusdisease, the casing shows spots com-pletely barren of mycelium; these areasfail to develop mushrooms. This“dieback” syndrome probably is relatedto high populations of nematodes ratherthan to the direct effects of viralinfection.

While the severe form of virus disease isdramatic, much of the economic impactis caused by the yield loss associatedwith the less severe form. This yielddepression can occur early on, beforethe grower suspects virus disease haseffected a crop. If the slight yield loss is

noticed at all, it may be confused withthe effect of suboptimal culturalconditions. It is critical that the growerarranges for clinical testing of the cropfor the presence of virus, to confirm theexistence of the disease once it issuspected.

Observations over the years have givenclues to the factors influencing theseverity of the disease:

● Generally, the greater the squarefootage of a bed showing diseasesymptoms and the earlier thesymptoms appear, the greater thecrop loss.

● The closer infection occurs to thetime of spawning, the more severethe disease. Contaminated compostproduces a severe infection if mixedinto noncontaminated compost atspawning.

Figure 37. Symptoms of virus disease. Shown is the characteristic “drumstick” syndrome involving elongated stems andsmall, misshapen caps.

● The earlier in the cropping cycleinfection occurs, the greater thecrop loss, since most mushroomsappear in the early breaks.

● All mushroom varieties are suscep-tible to virus disease. There isanecdotal evidence that brownstrains are more resistant than off-white and white hybrid strains,although the purported degree ofresistance has never been quantified.In the absence of resistant strains,control of the disease remains in thehands of the grower.

The Viruses

A trained researcher can detect manykinds of viruses “lurking” in mush-rooms, but very few viruses have anyknown impact on the appearance orgrowth of the mushroom. The same istrue in all the organisms that scientistshave studied. We also harbor manyviruses in our bodies that seem to haveno discernible effect on us at all, and weare concerned only about those thatcause disease.

The mushroom viruses that have beenstudied so far are composed of thegenetic information-encoding chemicalribonucleic acid (RNA). A protectiveprotein coat covers the RNA, but in thecase of the VV, a lipid membranereplaces the protein shell.

Viruses multiply to astronomicalnumbers within the cells of their host,but they lack the biochemical features todo so on their own. Consequently, theymust reproduce inside a host cell; ineffect, they take over the operations ofthe cell for their own multiplication.For this reason, viruses are considerednonliving “molecular pirates.” For thesame reason, mushroom viruses are nottransmitted as “free-living” particleswithin the compost, casing, or water,but rather are transmitted only fromwithin a living organism (i.e., mush-room spores and mycelium).

LIV is the infectious agent that has beenimplicated in virus disease. LIV is foundin all virus disease-affected mushrooms.MBV is not considered a cause of virusdisease. Research has shown that MBVis present in some healthy mushrooms,but it also is present in most, but notall, mushrooms affected by virusdisease—but never without LIV beingpresent too. LIV seems quite capable ofcausing disease without the assistance ofMBV. It is suspicious, however, thatboth MBV and LIV are detected inmost cases of virus disease. MBVconceivably could modify the severity ofthe disease symptoms or may causeanother type of disease not yet de-scribed. Or, it may have no effect on themushroom whatsoever. VV occurs inboth healthy mushrooms and thoseshowing virus disease symptoms, andfor this reason is thought to be benign.

The table below summarizes our currentunderstanding of the occurrence ofthese three viruses in healthy mush-rooms and in mushrooms showingsymptoms of virus disease.

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Incidence of the Virus in:

Virus Type Healthy Mushrooms Diseased Mushrooms

LIV <1% 100%

MBV ~5% ~60%, but only with LIV

VV 100% 100%

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Sources of Infection

LIV associated with virus disease istransmitted through spores and myce-lium of the mushroom. Transmission ofthe virus by infected mushroommycelium in the compost was investi-gated even before the viral nature of thedisease was known. It was shown thatinfected mycelium could, if introducedexperimentally or accidentally onuntreated wooden surfaces, carry thevirus into a healthy crop. The healthycrop then would develop the symptomsof the disease. Virus transmission byway of infected mycelium has beenassociated with severe disease outbreaks,possibly owing to the ability of themycelium to fuse quickly with thehealthy spawn and transmit the virus.

Spores now are believed to be the mostimportant mechanism for spread of thevirus. Spores are produced in prodigiousnumbers within mushroom farms. Onemushroom can discharge 1.3 billionspores, and spore discharge rates fromexhaust air can be as high as 3.7 billionper minute. Though diseased mush-rooms produce fewer spores thanhealthy ones, almost 70 percent of theviable spores discharged by diseasedmushrooms contain LIV. When adiseased spore germinates in compost, itsends out its own mycelium, which caninfect healthy mycelium (i.e., spawn).As rhizomorphs and mushroomsdevelop from the infected mycelium,the virus multiplies and spreadsthroughout the tissues, causing diseaseand infecting the new mushrooms andtheir spores. Picking mushrooms tightstops this disease-spreading cycle bypreventing the release of spores. Sincediseased mushrooms tend to open andrelease their spores prematurely com-pared to healthy mushrooms, growersmust be very diligent in their pickingpractices.

Spore-transmitted virus disease tends tobe less severe than mycelium-transmit-ted virus disease, possibly because of theextra time necessary for spores togerminate before infecting myceliumand spreading throughout a crop ofmushrooms. This delay is somewhatoffset by the large number of sporesavailable to carry the virus.

Patterns of Infection

Now that virus disease is recognized inits various forms, growers have beenable to discern certain patterns ofinfection. Historically, the diseasecommonly flared up when constructionon the farm disturbed a settlement ofvirus-infected spores. Typically, growersobserved the disease in crops that werebeing spawned at or near the time of theconstruction. More recently, outbreakshave been associated with a compostingproblem. Much like an indicator mold,virus disease shows that the compost isnot being heated uniformly to tempera-tures that are high enough to destroythe sources of the virus in the compost.

Clinical Diagnosis of VirusDisease

Clinical diagnosis of virus disease can bea critical part of an IPM program. Asnoted earlier, clinical diagnosis ofviruses in a crop is an important firststep in correcting an outbreak, espe-cially when the disease is manifesting itsmilder form. Testing for virus disease isuseful in other ways. The grower shouldroutinely test to determine if virusdisease is present but unnoticed incrops. This precaution can pay for itselfin reduced yield loss. Once a virusoutbreak occurs, the grower can usevirus testing to monitor the course ofthe infection to verify that controlmeasures are successful. How thistesting is performed has changed andimproved in recent years. Testing is nowextremely sensitive, available, andaffordable. Some commercial spawnmanufacturers offer virus diagnosis as acustomer service.

Early on, viruses were detected visuallyusing an electron microscope alone or incombination with antibodies(immunosorbent electron microscopy)that captured the virus particles, makingthem easier to detect. This testingprocedure is expensive, but it is stillused in parts of Europe.

Testing for the presence of certaindouble-stranded RNAs (dsRNAs), thegenetic component of the virus, waswidely practiced in the 1980s and wasthe research tool that led to the identifi-cation of LIV as the virus disease agent(Figure 38). This test was used at farmsto diagnose, detect, and monitor virusoutbreaks. Its use allowed growers totrack progress through the course ofoutbreaks, match results with controlpractices, and verify when virus out-breaks actually had disappeared.

Reverse-transcription polymerase chainreaction (RT-PCR) is the state-of-the-science test that now offers unsurpassedsensitivity for virus disease diagnosis. Inthis test, an enzyme to DNA firstconverts the viral dsRNA. Usinganother enzyme, the DNA then iscopied more than a million times,similar to using a photocopier. The largequantity of the copied DNA can bedetected easily in the laboratory, eventhough the original viral RNA fromwhich it was copied may have beenpresent in the mushroom tissue at levelstoo low to detect by other methods(Figure 38). Using RT-PCR, virustesting can be extremely sensitive, andfew virus episodes escape undetected.The test is of reasonable cost and doesnot require extraordinarily expensive labequipment.

Figure 38. Clinical diagnosis of virus disease. DsRNA analysis (left) and RT-PCRanalysis (right) of healthy (Hea) and diseased (Dis) mushrooms. DsRNA analysisdetects a vesicle virus dsRNA in healthy mushrooms, and numerous La Franceisometric virus dsRNAs in diseased mushrooms. RT-PCR detects only La Franceisometric virus in diseased mushrooms with the presence of a specific DNAproduct (arrow). DNA size markers are shown (Mkr).

Control Measures

Since there is no known commercialmushroom strain that is resistant tovirus disease, the grower must incorpo-rate virus disease preventative measuresinto the IPM plan and rigorously carryout the control measures. The followingpractices are recommended for diseasecontrol:

● Establish and strictly adhere to acomplete sanitation/hygieneprogram. Sanitation of surfaces,machinery, and clothing of workersis the foundation of the controlprogram. Disinfectants (quaternaryammonia solutions, iodine, phenolics,and chlorine) can be used in the cleaning regimes.

● Control the release and movementof spores to prevent them frominfecting new crops. Do not allowmushrooms on the beds to open;pick tight. Pick diseased crops last.

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Use HEPA air filters on productionroom air intakes.

● Attend to composting and pasteur-ization. Adequate and uniformpeak heats are necessary to killsources of infection in the compost(virus-infected spores and mycel-ium). Check routinely to ensurepasteurization with good peakheating during Phase II.

● Be careful to avoid contaminationduring spawning operations, andbe protective of spawned beds.Practice thorough sanitation duringspawning operations. Movement ofworkers should be restricted in thearea where spawning operations arecarried out and where spawn runcrops are growing. Use plasticsheets on beds during spawn run toprevent spores from falling on thecompost.

● Time-released supplementation atspawning may improve yields froma diseased crop, but is not asubstitute for any of the controlmeasures listed here. It cannotcontrol the disease.

● Steam off to kill sources of infectionsuch as mushroom spores andmycelium. Usually 160°F (71°C) inthe beds for 6 hours or more iseffective. Some growers use a 24- to48-hour steam-off. Double steamingthe house, once when full andagain when empty, has beenpracticed but probably is not anymore effective than steaming thehouse properly once.

The Future

Considerable success has been achievedin genetically engineering viral resis-tance in plants, and work is under wayto accomplish the same for mushrooms.The first highly efficient and convenientprocedure for transferring genes intoAgaricus bisporus recently was developed(C. P. Romaine laboratory). Throughmolecular biotechnology, the breedingof viral-resistant mushroom strains, aswell as strains with wide-ranging noveltraits, now is within our grasp.

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Contributors

Phillip S. Coles, project coordinator andcontributor, project manager, GiorgiMushroom Company, and chair,Integrated Pest Management Commit-tee, American Mushroom Institute

William Barber, growing manager,Giorgi Mushroom Company

David M. Beyer, assistant professor ofplant pathology, The Pennsylvania StateUniversity

Shelby J. Fleischer, associate professor ofentomology, The Pennsylvania StateUniversity

Cliff Keil, associate professor of ento-mology and applied ecology, Universityof Delaware

Danny Lee Rinker, associate professor,mushroom specialist, HorticulturalResearch Institute of Ontario

C. Peter Romaine, professor of plantpathology, The Pennsylvania StateUniversity

Susan P. Whitney, extension specialist inentomology and applied ecology,University of Delaware

Paul Wuest, professor emeritus of plantpathology, The Pennsylvania StateUniversity

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