Greenhouse Sanitation And Pest Exclusion

By J. Raymond Kessler Jr., Auburn University

Implementation of new Worker SafetyProtection Standards, increases in pesticidecosts, and concerns about liability andenvironmental contamination from pesticideshave combined to increase both the cost and

complexity of greenhouse pest managementprograms. These increases should encouragegrowers to re-examine how they control pestsand to look for methods that reduce chemical

usage.

Two frequently overlooked or under used concepts for pestmanagement that deserves consideration is sanitation and pestexclusion. Both concepts, when applied aggressively, use nochemicals other than disinfectants, have no restricted entry interval,are often cost effective, are relatively easy to implement, and canreduce the need for pesticides. They operate on the basicphilosophy that it is easier to prevent or exclude pest problems inthe first place than to treat them once they occur.

A management philosophyEffective greenhouse sanitation requires a commitment bymanagement to establish a certain "state of mind" or "awareness"in employees. This involves establishing in the minds of everyonethose areas that should be treated as "clean areas" or "dirty areas."Employees should be trained from the first day to recognize pestproblems, where those problems come from, how they spread,and what employee behaviors are appropriate within clean areasto prevent pest problems. Management should then monitor theareas closely to determine the effectiveness of training.

Management should identify different levels of cleanliness andassign areas in the greenhouse and product area to those levels.For example: Level 1 (most clean) is anything that comes in contactwith the plants or potting media such as containers, cutting knives,work tables for processing cuttings, potting media storage, etc.Level 2 (next clean) is anything that comes in contact with thecontainers such as bench tops, conveyer belts or carts that transportcontainers, container storage, etc. Level 3 (dirty) are other areasof the production and growing. Level 4 (most dirty) is outside theproduction and growing area including things that are brought infrom outside. Objects should always move within a cleanlinesslevel or from a clean to dirty level but never from a dirty to cleanlevel without disinfection. For example, if a watering wand andbreaker fall from the bench top (level 2) to the floor (level 3), donot put it back on the bench top without disinfection.

Between crop cleanupGreenhouse cleanupbetweencrops canserve to preventthecarryoverof pestproblems to the nextcrop andeliminatethe life-stagesof insects anddiseasesthat aredifficult tocontrol usingpesticides.Though it is best to perform a cleanup between each crop, athorough job can usually be accomplished during the summer, in

Page 8

December between the poinsettia and spring bedding crops, oranytime the greenhouse is empty for a day or two. Consider thefollowing suggestions: 1) Remove all debris from the benches andfloors. Bench tops and solid floors can be swept, vacuumed or steamcleaned. Vacuuming has the advantage of picking up weed seedand spores without blowing dust into the air, which is a disadvantageof sweeping. Many growers take pride in having their employeessweep main isles. However, sweeping an isle under the greenhouseintake vent blows dust and spores into the ventilation air streamthat is carried into the crop canopy. Bench tops can be treated witha greenhouse disinfectant. 2) Remove all weeds from the greenhousefloor. Herbicides registered for greenhouse use can be appliedaccording to label directions. The following is a list of herbicidesfor greenhouse use:

Roundup Pro: Non-selccti ve, systemic, slow control, turn off fansduring application, cannot be used when desirable cropsarc present!

Finale: Non-selective, contact, turn off fans during application, canbe used when desirable crops are present, cannot be usedon eatable crops.

Scythe: Non-selective, contact, works best on young weeds and at80EF or higher, can be used when desirable crops present,can be used for algae and moss control in cooling pads.

Reward: Non-selective, contact, works best on young weeds, canbe used when desirable crops present, cannot be used oneatable crops.

3) Prevent wet areas on the floor by repairing leaking pipes, solenoidvalves, or faucets and correcting poor drainage areas. Cover dirtfloors with gravel and weed barrier. If the gravel is put down first,then covered with weed mat, it is easier to clear the floor surface of

debris. 4) Disinfect fertilizer stock tanks, greenhouse trashcans, andall watering devices including watering wands and breakers andthe ends of drip irrigation tubes. Scrub and disinfect propagationarea floors, bench tops, pipes, and mist nozzles. Clean or replaceevaporative cool-cells at the first sign of ware. 5) If possible, cleanthe greenhouse, wetdown the interior, and close it for a fewdays toa week with little or no ventilation to solarize the greenhouse.Wetting the floor willencourage weedseeds and sporesto germinateand high sunlight and temperature will naturally pasteurize thegreenhouse interior.

Start pests free

Start with pest-free plant material. Seeds can carry pests on theseed coat or in the embryo so purchase only the best quality seedfrom reputable seed producers. In many cases, the higher cost ofgood quality seed is worth the peace of mind. Keep records of seedsources and lot numbers, and track the crops during production sothat if a problem arises, it can be traced back to the supplier.Likewise, purchase only pathogen indexed, vegetative materialpropagated from "elite" stock plants. Pathogen indexing is a tissue

SoutheasternFloriculture, November/December, 2003

culture procedure thateliminates systemic bacteria, viruses, andfungi from plant materials. Itdoes costs more, but don't get burnedby cheaper, non-indexed material!

Pest exclusion involves any measure that can be taken to preventthe introduction of pests into the greenhouse. Implementation ofexclusion should begin with thearrival of new plant material. Allincoming plants, seedlings, orcuttings (rooted orunrooted) shouldbe examined carefully for diseases or insects by an individualtrained to locate and identify these problems. Plant materialshipments found tobe infected should be reported to the supplierand not allowed in the greenhouse or productionarea.

Growers involved in certain types of production or certain cropssuch as geranium propagation and stock plant production shouldisolate incoming plant material for a period adequate to ascertainif the plants are clean. Many growers establish a free standing,"quarantine" greenhouse toisolate plants for afew days toaweek.Trained employees inspect the plants daily and treat problems ifthey arise. These employees should attend the quarantinegreenhouse at the end of the day and go home afterward withoutreturning to the mainproduction facility.

After potting, isolate crops known tohave problems. Forexample,place all plants from a shipment of cutting geraniums in onegreenhouse and keep shipment together. Do not place susceptiblecrops onthe same irrigation system with other susceptible crops.This is especially important when sub-irrigation is used. Isolate

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susceptible crops byplant source andshipment by3 feet. A"buffercrop" that is not susceptible can be placed in the space betweensusceptible crops.Avoid hanging basketsover susceptible crops.

During the cropAgain, beaware ofdirty and clean areas. The following isa listofsanitation primers: 1) Wash any tools, containers, or equipmentthat may be reused on plant material or come in contact withgrowing medium with a greenhouse disinfectant. 2) Insist thatemployees wash their hands before beginning operations thatinvolve contact with plant materials, potting mix, or containers.Provide convenient washing stations with hotwater, soap, fingernailbrushes, and paper towels. 3) Keep hose-ends hung up. Irrigationequipment should beconsidered part of the level 1clean area. 4)Bench tops should beconsidered a level 2 clean area. Keep dirtyequipment, feet, etc. offthe benches. If standing onbench tops isnecessary foroverhead repairs, disinfect thebenches afterward. 5)Avoid wearing brightly colored clothing, especially yellow andblue, thatattractsinsectsthat mayhitcha ride into the greenhouse.6)All weeds should bekeptoffthefloors andpulled from growingcontainers. Place trashcans in each greenhouse and insist they beused and emptied daily. 7) Provide clean aprons for employeesthat work inpropagation areas. 8)Infected, diseased, orsuspiciousplants should be removed with minimal disturbance from thegreenhouse inplastic bags ora covered container. Remove plantsshowing symptoms and adjacent plants without symptoms becausethey may already be infected. 9) Avoid activities that result insplashing water from plant toplant where possible. Avoid activities

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that result in excessive dust in the greenhouse. 10)Scout for pestsproblems frequently and take corrective measures quickly. This isespecially important for thrips, whiteflies, and aphids that are knownvectors of systemic bacteria and viruses. 11)Do not allow customeror employee house plants to be stored in the production greenhouse.

Production areas

Sanitation should extend beyond the greenhouse to production andstorage areas. Avoid storing media and media components outdoorswhere the bales can get torn or damaged and exposed to sources ofinsects, disease spores, or animals. A warehouse with enclosed bensor shelters will keep media dry and protected from pests. If outdoorstorage is unavoidable, raise the bales off the ground on palletsand cover the stacks of bales tightly with heavy tarp or plastic.Likewise, avoid storing containers (pot, flats, or tags) outdoors.

Greenhouse media comes from the supplier reasonable sterile. Itdoes not make sense, therefore, to put that media in used containers.This is especially true for crops that have a history of problemssuch as pansies or geraniums. Having said that, many growers dodisinfect and reuse containers. If so, be sure a system is set up toremove all old media and debris from containers before dippingthem in disinfecting solution. Lastly, keep the production area cleanand organized. Periodically, sweep or vacuum and wash the floors.Never re-use potting media that has fallen on the floor. Pottingequipment, benches, belts, machines, etc. should be hosed off andwashed with greenhouse disinfectant at the end of the work day or

before working with acropknown tohaveproblems. Thefollowingare properties of severalcommonlyusedgreenhouse disinfectants:

Alcohols (isopropyl): Denaturesproteinsand hasslowgermicidalactivity. Phytotoxic to some plant material, evaporates,and is flammable. Good for small jobs such as sterilizingcutting knives, pruners, and small work surfaces.

Chlorine Bleach: A 10% solution is highly effective as abactericide, fungicide, and algicide (less as a sporicide).Good for dipping containers and washing benches andequipment. Corrosive to metals such as galvanizedbenches and has a short use life (2 hours). Should not beexposed to sunlight and is deactivated by organicmaterials.Releases chlorine that can irritateshin andeyes.

Quaternary ammonium compounds (Greenshield): A cationicdetergent good for cleaning surfaces. Deactivated byhousehold soaps that are anionic detergents. Effective asa bactericide, fungicide, and algicide (less as a sporicide).Noncorrosive, stable, inexpensive, and relative non-toxic.Phytotoxic to plant material. Greenshield can be appliedwith an injector. EPA approved.

ZeroTol: Effective as a bactericide, fungicide, algicide, andsporicide. Low toxicity, EPA approved, corrosive above5%, but can be applied to plant material at lowerconcentrations. Environmentally friendly becausebreakdown releases water and oxygen.

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Page 10 Southeastern Floriculture, November/December, 2003

Keeping the outside ... outExclusion frequently involves physical barriers to pest entry intothe greenhouse.Often, the main problem is to recognizehow insectsor diseases gain entry. The following are some tips: 1) Make surethegreenhouse glazing material is free of holes, tears,or leaks thatcould allow insect or disease entry. 2) Entry-way doors into thegreenhouse should seal and automatically close. 3) Install andmaintain exterior or interior louvers over fans that close when thefans are not operating. 4) Exclude pets and rodents from thegreenhouse. Animals canbring in insects anddiseases on theirfeetor their fur. 5) Consider the installation of insect screens over ventsto prevent the entry of thrips, white flies, etc. This installationrequires careful planning to insure that adequate ventilation ismaintained. Check the insect screening weekly and keep it clean.6) Keep areasaroundthegreenhouse free of debrisandconsistentlymowed before vegetation forms seed. Many growers also removeall plant material for a distance of ten to twenty feet around thegreenhouse and cover this area with concrete or gravel to limitweed seed, insect, and disease entry. Weeds that emerge in thevegetation free areacanbe treated withSurflan (preemergent) plusRoundup Pro, Finale, Scythe or Reward. Follow label directionsfor applying these herbicides. Be sure to close all vents and turnoff fans when applying herbicides, mowing, or using a weed eateraround the greenhouse. Employees who do cleanup work outdoorsshould shower and change cloths before re-entering the greenhouse.If the work can be done toward the end of the workday, they cango home afterward.7) Do not landscape with trees or shrubs nextto the production greenhouse.

Friends and neighborsPeople can unknowingly pick up pests from outdoors and bringthem into the greenhouse. Do not allow customers to shop in theproduction greenhouse. Growers who want to sell at retail shouldestablish a retail area separate from the production facility.Wholesale buyers, sales reps, and extension personal often visitseveral greenhouse businesses as part of their jobs each day.Growers may not wish to exclude these individuals from thegreenhouse but the potential for bringing pests into the greenhouseexists. At the very least, provide these individual an escort, limittheir activities, and ask them to wash their hands before entering

the greenhouse.

Implementation ofjudicioussanitation and pestexclusion practicesinthegreenhouse cancontrolor helpmanage manyof the problemsgrowersface while reducing the need for chemical pesticides.Allthingsconsidered,thesepracticesmay becomemorecosteffectiveas the costs of pesticide application increases. However, there isone additional benefit.Most peopleare moreproductiveand happierin a clean working environment. If cleanliness practices arepresented to employees with a positive "can do" attitude, manypeople find additional ways to apply the concepts and encourageothers to follow their example.

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