INSECT PESTS OF FIELD CROPS

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COOPERATIVE EXTENSION SERVICECollege of Agriculture

The University of WyomingDEPARTMENT OF PLANT SCIENCES

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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30,1914, in cooperation with the U.S. Departmentof Agriculture, Glen Whipple, Director, Cooperative Extension Service, University of Wyoming Laramie, WY. 82071.

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INSECT PESTS OF FIELD CROPS

Chris C. BurkhardtProfessor of Entomology

Revised by

Mark A. FerrellExtension Pesticide Coordinator

and

Tim ChristiansenExtension Entomologist

TABLE OF CONTENTS

SECTION I - Principles of Field Crop Insect Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

SECTION II - Causes of Insect Outbreaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

SECTION III - Types of Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A. Biological . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1B. Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2C. Legal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2D. Cultural . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2E. Reproductive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3F. Chemical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3G. Integrated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

SECTION IV - Major Field Crop Pests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3A. Major Pests of Corn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1. Corn Rootworms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. Mites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

B. Major Pests of Alfalfa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41. Alfalfa Weevil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42. Pea Aphids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53. Lygus Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

C. Major Pests of Beans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61. Mexican Bean Beetle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

D. Major Pests of Small Grains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61. Grasshoppers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62. Pale Western Cutworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73. Wheat Curl Mite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74. Russian Wheat Aphid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

E. Major pests of Sugar Beets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81. Sugar beet Root Maggot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82. Beet Leafhopper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

F. Major Pests of Potatoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91. Potato Psyllid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92. Colorado Potato Beetle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93. Potato Flea Beetle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10PICTURE SHEET NO. 4 - Corn Insects Above Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10PICTURE SHEET NO. 5 - Corn Insects Below Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10PICTURE SHEET NO. 7 - Common Small Grain Insects . . . . . . . . . . . . . . . . . . . . . . . . . . 10PICTURE SHEET NO. 8 - Common Forage Legume Insects . . . . . . . . . . . . . . . . . . . . . . . . 10PICTURE SHEET NO. 9 - Common Vegetable Insects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Insect Pests of Field Crops

Chris C. BurkhardtProfessor of Entomology

SECTION I - Principles of Field Crop Insect Control

Present-day insect problems, created or aggravated bythe concentrations of host plants, are diverse and complexand without simple solutions. Farmers and ranchers mustfollow the instructions and advice of competent fieldmencarefully in order to cope effectively with damaging pestpopulations. Specialists who disseminate controlinformation must be able to adapt the lowest cost programwhich is not hazardous to man and domestic animals, andwhich does not cause undesirable side effects in theenvironment.

A knowledge of insect classification, growth anddevelopment, and life cycles is a requisite to the conduct ofcontrol programs. Life cycle data are essential in the timingof controls. One of the most familiar principles of insectcontrol is that of the "weakest link". Only through athorough knowledge of a pest's life cycle can one hope toaim control measures effectively at its most vulnerable stage.

Crop value, or the unit value of an agricultural crop, isan important consideration. Control of pest insects isusually justifiable when the increase in marketable yieldproduced is worth more than the cost of control. In the caseof low-unit-value crops, such as certain forage crops, thefeasibility of controlling pests is difficult to determine.Costly controls can be applied more logically to floral cropsand fruit crops than to field crops and cereals.

Preventive control measures can be applied when oneknows through experience that a certain insect pest or pestswill develop to a damaging degree in a given area year afteryear. It is often true that early season applications are moreefficient than later ones. Early treatments tend to control apest species before it has reached its maximum rate ofdevelopment and reproduction; and before the crop foliagehas grown to the point where it is difficult to penetrate withsprays, granules or dusts. In contrast, one should generallywait until a certain pest population level is reached beforetreating field crops.

Current development of new insecticide formulationsand types of application equipment has gone hand in handwith the appearance of new insecticides.

SECTION II - Causes of Insect Outbreaks

Outbreaks or epidemics of insect pests are usuallycaused by one or more of the following:

1. Large-scale culture of a single crop.

2. Introduction of a pest into a favorable new area

without its natural enemies.

3. Favorable weather conditions for rapiddevelopment and multiplication of a pest; thesesame conditions may also be unfavorable to naturalenemies.

4. Use of insecticides which kill the natural enemiesof a pest, exert other effects favorable to a pest, orreduce the competing species of a pest whileallowing it to multiply unmolested or only partiallycontrolled.

5. Use of poor cultural practices which encouragebuildup of pest infestations.

6. Destruction of natural biotic communities whichotherwise provide regulation of insect populationlevels.

SECTION III - Types of Control

A. Biological control can be defined as the action ofparasites, predators, or pathogens (disease producingorganisms) on a host or prey population, producing alower population level than would prevail in theabsence of these agents. Generally biological controlrefers to manipulations by man, and distinguished fromnatural enemies and natural control.

Biological control has a number of distinctadvantages, three of which are permanence, safety, andeconomy. Once biological control is established, it isrelatively permanent and has no side effects, such astoxicity, environmental pollution, or use hazards. Thereare three main kinds of traditional biological control:

1. The introduction of exotic species of parasites,predators and pathogens.

2. Conservation of parasites and predators.

3. Augmentation of parasites and predators.

The use of insect pathogens, such as fungi,bacteria, and viruses, is another one of the techniquesemployed in the biological control of insects.

From the practical standpoint, it should be notedthat natural enemies should be able to play a role inmost crop ecosystems. One factor which may impedetheir effectiveness is climate. This is particularly truein Wyoming. Other reasons their activity may beinhibited include environmental factors such as dust,

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competitors, drift of pesticides from adjoiningagriculture, or necessary pesticide use within the crop.

Biological controls are not suitable in many pestsituations. It takes time for the parasites and/orpredators to reproduce sufficiently to bring the pestunder control. A farmer often feels that he cannot waitfor the natural enemy to do the job; he needs amarketable crop each year. Other technical difficultiesinvolve such items as determination of which parasitesor predators to introduce, whether to use more than oneparasitic species at a time, how to eliminate secondaryparasites that prey on the beneficial form, and whethera program of continuous liberations may be feasible.Then there is always the problem of protecting suchpredators and/or parasites from insecticides.

B. Mechanical control is the reduction of insectpopulations by means of devices which affect themdirectly or which alter their physical environmentradically. These methods are often hard to distinguishfrom cultural methods. However, mechanical controlsinvolve special physical measures rather than normalfarm practices. They tend to require considerable timeand labor and often are impractical on a large scale.

Hand picking, shingling, and trapping are familiarmechanical methods of insect control. Screens,barriers, sticky bands, and shading devices representother mechanical methods; while hopper-dozers anddrags are specialized equipment for collecting orsmashing pests.

C. Legal control is the lawful regulation of areas toeradicate, prevent, or control infestation or reducedamage by insects. This involves mainly the use ofquarantines and pest control procedures. Federal andstate officials often work with legally established local,community, or county districts, as in grasshoppercontrol projects.

D. Cultural control is the reduction of insect populationsby the utilization of agricultural practices. It has alsobeen defined as "making environments unfavorable forpests". The method more or less associated withagricultural production usually involves certain changesin normal farming practices rather than the addition ofspecial procedures.

Knowledge of the life history or bionomics of apest species is essential to the effective use of culturalcontrol methods. The principle of the "weakest link" ormost vulnerable part of the life cycle usually applies.The environment is changed by altering farmingpractices at the correct time so as to kill the pests or toslow down their multiplication. In this way, the methodis aimed more at prevention than at cure.

Since cultural methods are usually economical,

they are especially useful against pests of low-unit-value crops. Such methods are particularly applicableto field crops.

Several types of cultural control practices are:

1. Rotation. Certain kinds of crop rotations may aid inthe control of pests. Insects which are reducedeffectively by rotations usually have a long lifecycle and a limited host range and are relativelyimmobile in some stage of their development.Changing crops in a rotation system isolates suchpests from their food supply. Wireworms, whitegrubs, and corn rootworms are good examples.

2. Location. Careful choice of crops to be plantedadjacent to each other may help reduce insectdamage.

3. Trap Crop. Small plantings of susceptible orpreferred crop may be established near a majorcrop to act as a "trap". After the pest insect hasbeen attracted to the trap crop, it is usually treatedwith insecticides, plowed under, or both.

4. Tillage. The use of tillage operations to reducepopulations of soil-inhabiting insects may work inseveral ways; change physical condition of soil,bury a stage of the pest, expose a stage of the pest,mechanically damage some stage of the insect,eliminate host plants of the pest, and hasten growthor increase vigor of the crop.

5. Clean Culture. Removal of crop residues, disposalof volunteer plants, and burning of chaff stacks aremeasures commonly applied against vegetable andfield crop insects.

6. Timing. Changes in planting time or harvestingtime are used to keep the infesting stage of a pestseparated from the susceptible stage of the host.

7. Resistant Plant Varieties. The sources ofresistance to insects in crops have been classifiedas non-preference, antibiosis, and tolerance. Insectpreference for a certain host plant is related tocolor, light reflection, physical structure of thesurface, and chemical stimuli such as taste andodor.

Antibiosis is defined as an adverse effect ofthe plant upon the insect. This may be causedeither by the deleterious effect of a specificchemical or by the last of a specific nutrientrequirement.

Tolerance is the term applied to the generalvigor of certain plants which may be able towithstand the attack of pests as sucking insects.

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Tolerance also includes the ability to repair tissuesand recover from an attack.

Advantages of the use of resistant varieties includea cumulative and persistent effect which ofteneliminates pest damage within a few seasons, lack ofdangers to man and domestic animals, low cost (oncethe program is established), and utility in integratedcontrol systems.

E. Reproductive control is the reduction of insectpopulations by means of physical treatments orsubstances which cause sterility, alter sexual behavior,or otherwise disrupt the normal reproduction of insects.

F. Chemical control is the reduction of insect populationsor prevention of insect injury by the use of materials topoison them, attract them to other devices, or repelthem from specified areas.

Chemicals are still our first line of defense in themanagement of most pests, despite adverse publicity.They are highly effective and economical, and can beapplied quickly to have an immediate impact on a pestpopulations. When pest populations approacheconomic levels, and natural controls are inadequate,pesticide applications are the only hope to save a cropso that it can be marketed. It seems clear that pesticidesmust and will continue to be used in a major way inintegrated pest management.

Pesticides are at this point in time, essential for:

1. The maintainence of adequate crop protection

2. The protection of forest resources

3. The preservation of man's health and wellbeing.

One of the advantages of the use of insecticides inmany crop ecosystems is that more than one major pestmay be controlled with a single application.

The judicious use of chemical pesticides is acritical part of pest population management. Chemicalpesticides are especially important as short-term pestmanagement tools. The important consideration is thatpesticides be used when possible in a manner that isharmonious with other elements of the agro-ecosystemand augmenting other control agents.

Insecticides do have certain well known limitationswhich can be briefly listed as follows:

1. Development in many cases of strains of peststhat are resistant to pesticides.

2. Only temporary control effects on pest

populations, often necessitating repeatedtreatment.

3. Presence of residues of the pesticide in theharvested crop.

4. Outbreaks of unleashed secondary pests,resulting from the destruction of their naturalenemies.

5. Undesirable side effects on non-targetorganisms, included a) parasites andpredators; b) fish, birds and other wildlife; c)honey bees and other necessary pollinators; d)man and his domestic animals, and e) the cropplant.

6. Direct hazards in the application of certaininsecticides.

7. Reduction and simplification of the arthropodcomponent of the agro-ecosystem.

The various specific hazards, as well as differentformulations of insecticides and types of equipment toapply them are covered elsewhere in this manual orguide book.

G. Integrated control is the management of insectpopulations by the utilization of all suitable techniquesin a compatible manner so that damage is kept beloweconomic levels. It is an ecological approach that notonly avoids economic damage but also minimizesadverse effects. Principal considerations of theintegrated approach to pest management are the agro-ecosystem, the economic threshold, and the leastdisruptive program.

SECTION IV - Major Field Crop Pests

In the remainder of this section, the identification, lifehistory, damage, pesticides, pesticide use and environmentalconsiderations are presented for only the major insect orarthropod pests of corn, alfalfa, beans, small grains, sugarbeets, and potatoes.

Specific insecticide control recommendation on thevarious insecticides, formulations and rates for all insectpests of field crops are covered in the Wyoming AgriculturalExtension Service Bulletin 543R entitled "Control of FieldCrop Insects".

A. Major Pests of Corn

1. Corn Rootworms

a. Identification (see color illustrationsPicture sheets No. 4 & 5 in the appendix)

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Larvae slender white or pale yellow, 3/10to 4/10 inch long.Pupa white and fragile.Adults (beetles):

Western -1/6-1/4 inch long,yellowish green with three darkstripes or a large dark area on hardwing covers.

Northern - 1/6 to 1/4 inch long,uniform green to yellowish green incolor.

Southern - slightly larger than above;yellowish green with all black spotson back.

b. Life HistoryWestern and northern - overwinter aseggs in the soil. One generation per year.Southern over-winters as adults - mayhave two or more generations per year.

c. DamageLarvae feed on roots; prune roots, causelodging. Adults feed on leaves, tasselsand silts - may interfere with pollination.

d. PesticidesPrimarily organophosphorus andcarbamate. Some fairly toxic - mostlyshort residual almost entirely granularformulations.

e. Pesticide UseShould not be used on first year corn norwhen rotating crops. When necessaryshould be used only as granules appliedin a 6-7 inch bank over the row preferablyat planting time or in some cases as acultivation (lay-by) treatment.

f. EnvironmentGranules, if in contact with seed, maycause some phytoxicity. Slightly lighterdosages may suffice in light sandy soil.Heavy soils or soils with high organicmatter of pH may require higher rates.Moisture is necessary to activategranules. Non-target organisms are not aproblem. Do not apply spray for adultcontrol unless pollination is threatened.

2. Mites (especially Bank's grass mite)

a. IdentificationMinute, whitish, eight-legged, varyingsizes up to 1/60 inch long.

b. Life HistoryUsually overwinter as adults in debris.Several generations per year.

c. DamagePrimarily from sucking sap, destroyingchlorophyll and causing leaves to dry upand die. Usually start at lower leaves andmove progressively upward.

d. PesticidesSystemic insecticides applied as granulesin the whorl or phosphates as foliarsprays.

e. Pesticide UseShould not be used routinely. Watch forsigns of infestation. Non-economic ifonly on the lower set of leaves. Becauseof height of corn, chemicals may have tobe applied by airplane.

f. EnvironmentMite build up is usually associated withhot, dry conditions. Same conditions maydecrease efficiency of chemicals. Toavoid drift from wind and evaporation,may be best to apply mornings andevenings. Some probability of hittingsuch non-target insects as lady birdbeetles or lace-wings, especially withnon-systemic materials.

B. Major Pests of Alfalfa

1. Alfalfa Weevil

a. Identification (see color illustrations PictureSheet No. 8 in appendix). Larva is yellow(about 1 mm long) with shiny black headwhen first hatched. Full grown larva islegless, about 3/8 inch long, and green with abrown head and a white stripe down middle ofback.

Pupae are tan and encased in small flimsylace-like cocoons. Adults about 3/16 inchlong, light brown with a broad, dark brownstrip extending from front of the headposteriorly along middle of the backapproximately 2/3 to 3/4 length of body.Older weevils are gray or brownish black.

b. Life HistoryOverwinter mostly as adults. Eggs laid inspring in alfalfa stems. Larvae hatch. Usuallyone generation per year with considerableoverlapping in stages.

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c. DamageLarvae feed on foliage, especially terminalleaf buds. Skelentonize leaves giving grayishor frosted appearance. Stunts plants andreduced yield and quality.

d. PesticidesMostly phosphates and carbamates applied assprays. Some fairly toxic to man andbeneficial insects.

e. Pesticide UseShould not be used routinely. If damageoccurs within 10 days of harvest, shouldharvest early. Use resistant varieties of alfalfawhere possible and avoid use of pesticides. Ifnecessary, apply early morning or evening.Carefully observe waiting periods.

f. EnvironmentApply chemicals during favorable climaticconditions. Check for beneficial insects suchas predators, parasites and various kinds ofpollinators. If these are abundant, try to avoiduse of insecticides.

2. Pea Aphids

a. Identification (see color illustration PictureShee No. 8 in appendix). Small green, long-legged, either winged or wingless soft bodiedinsects no larger than 1/6 inch long.

b. Life HistoryOverwinter as eggs or female adults on alfalfaor clovers. In spring migrants spread to peasand other plants as well. Winged females givebirth to active young nymphs. May be manygenerations per year. In fall, males andfemales appear. Mating and egg laying takesplace. Most of them overwinter as eggs.

c. DamageSuck the sap and possibly also poison theplant. May cause wilting and reduction ofquantity and quality of hay on either first orsecond cutting of alfalfa.

d. PesticidesPrimarily organophosphorus insecticides,some systemic, some non-systemic, applied assprays. Mostly short residual or none, butwaiting periods must be followed where theyexist.

e. Pesticide UseUse only if aphids are numerous. Earlyharvest or use of resistant varieties mayeliminate use of insecticides.

f. EnvironmentApply preferably in morning or evening butnot if temperatures are below 50oF. Suchtiming is less detrimental to beneficial non-target insects as predators, parasites andpollinators. Systemic insecticides are moreselective against the target insect.

3. Lygus Bugs

a. IdentificationAdults about 1/4 inch long, have four wingsthat lie more or less flat over the back, and aremarked by a distinct "V" on the back just infront of the wings. Color may be light green,various shades of brown, or almost black.Nymphs have black spots of various sizes andnumbers on their backs.

b. Life HistoryEggs, nymphs and adults. Overwinter ashibernating adults; mate in spring; females layeggs in alfalfa stems. Two to five generationsa year.

c. DamageForage production and quality of hay areaffected. Most serious damage is in seedproduction. Cause buds to die, flowers todrop, immature seeds to shrivel, becomediscolored and fail to germinate when planted.

d. PesticidesMostly short residual, slight to moderatehuman toxicity, organophosphorusinsecticides, including some systemics. Alsothe carbamate carbaryl. All are non-persistent.

e. Pesticide UseFor forage, may cut a little early and avoid useof insecticides. If heavy infestations, applyinsecticides in bud sage of growth. For alfalfaseed production, time application with budstage or early bloom to kill newly hatchingnymphs.

f. EnvironmentMajor concern here are the non-targetorganisms. These include parasitic wasps andflies, predators such as lady bird beetles,lacewings, damsel buds, bigeyed bugs andpirate bugs as well as pollinators such as alkalibee, leafcutter bees, bumble bees, and honeybeets. Use chemicals only as necessary.Contemplate using a plant systemic insecticideor something like trichlorfon which isrelatively non-toxic to most beneficial insects.Morning or evening applications are less

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detrimental to beneficial insects buttemperature should be above 50oF. Waitingperiods between last application and harvestshould be carefully observed.

C. Major Pests of Beans

1. Mexican Bean Beetle

a. Identification (see color illustration PictureSheet No. 9 in appendix). Adults are stronglyconvex beetles about 1/4 inch long. The wingcovers (elytra) are usually copper red in colorand are conspicuously marked with 16 blackspots arranged in 3 rows over the back.Larvae are yellow and covered with dark,branched spines, fully grown they are about1/4 inch long.

b. Life HistoryOverwinter as hibernating adults (beetles) inlitter, trash or other protected areas. Femalesfly to bean fields in spring to deposit eggsafter plants are up. Usually one generation peryear in this area.

c. DamageBoth larvae and adults chew off portions ofthe bean leaf, masticate it, and suck the plantjuices. Usually feed from the under surface ofthe leaves. As leaf tissue drys, the unbrokenupper membrane tears apart.

d. PesticidesNumerous organophosphate materials havelabel approval, some systemic and some non-systemic. Even the chlorinated hydrocarbonmethoxychlor can be used. Carbaryl (acarbamate) may be used.

e. Pesticide UseThis pest is difficult to control primarilybecause both larvae and adults live and feedon the undersides of bean leaves where it isdifficult to apply insecticides. Thoroughcoverage of the plants with spray increasesefficiency of insecticides applied.

f. EnvironmentA community control program is advisable. Itis wise to burn or otherwise destroy all cropresidue soon after beans have been picked.Plowing under refuse at least six inches deepdestroys all stages of the beetle. Beansplanted three to four inches apart produce lessfoliage, are easier to treat and as a general ruleare not as heavily infested. Some resistantvarieties have been developed. Non-target

predators and parasites such as the tachinid flyand a small parasitic wasp are not a factor inWyoming.

D. Major Pests of Small Grains (esp. wheat)

1. Grasshoppers

a. Identification (see color illustration PictureSheet No. 7 in appendix). There are severalspecies of grasshoppers which attack smallgrains. These include the migratorygrasshopper, the differential grasshopper andthe two-striped grasshopper.

b. Life HistoryIn general most species overwinter in the eggstage as egg pods in the soil. Eggs hatch intonymphs and nymphs develop into adults.Most species have one generation per year.

c. DamageGrasshoppers relish small grains and injuryusually consists of defoliation or destructionof the plant. This may involve feeding onleaves or biting through the stems of smallgrains, severing the heads, feeding on ripeningkernels and thereby causing extensiveshattering.

d. PesticidesA few chlorinated hydrocarbons but mostlycarbamate and organophosphorus insecticides(mostly non-systemic) are used applied mostlyas sprays. A few are available in baitformulation. Malathion ULV at 8 fl. oz. peracre applied by air has been economical andsuccessful.

e. Pesticide UseAll insecticides should be applied early whilehoppers are young and usually concentratedbreeding or hatching areas. Insecticides aremost effective as broadcast sprays with lowgallonage sprayers. Granules of certainsystemics may be applied in the furrow atplanting time to protect seedlings.

f. EnvironmentThere are many natural enemies such aspredators and parasites of grasshoppers.There are robber flies, wasps, spiders, rodents,birds, tachinid flies, flesh flies, bee flies,blister beetles, and ground beetles. Culturalmethods include 1) elimination of weeds, 2)planting resistant crops, 3) tilling land infestedwith eggs, and 4) timing of seeding. Limiteduse insecticide such as treating field margin or

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only a few swaths at edge of field save moneyand cause less pollution.

2. Pale Western Cutworm

a. IdentificationThe larva is grayish, unmarked by spots orstripes; the skin has fine, flat, pavement-likegranules. Adult is a gray medium sized mothor "miller".

b. Life HistoryEggs are laid in soil in the fall and overwinteras eggs. Hatch in late winter or very earlyspring, sometimes while there's still snow onthe ground. Larvae feed along drill row,mostly underground. Inactive in June andJuly, pupate in August and adults are out inSeptember. One generation per year.

c. DamageLarvae feed in crowns and on undergroundportions of the wheat plants. Causes pruningof plants, some loss of stand and stunted andunthrifty plants.

3. Wheat Curl Mite

a. IdentificationVery small eriophyrid mite, white, spindle-shaped with only four legs near the anteriorend of the body. Mites are so small they arebarely visible magnified 10 times.

b. Life HistoryReproduces parthenogenetically (without thenecessity of males). Overwinter on grasses orvolunteer wheat.

c. DamageSome damage from sucking sap but majordamage because mites are vectors of the viruscausing wheat streak mosaic.

d. PesticidesSee B-543R Control of Field Crop Insects.

e. EnvironmentHail belt areas are in greatest need ofprotection from wheat curl mites and wheatstreak mosaic. Controlling volunteer wheatwill help. Late planting may also be of somehelp. Formulation, and method of applicationdo not present a hazard to non-targetorganisms.

4. Russian Wheat Aphid (RWA)

a. Identification (see drawing). Small, light-green aphid with an elongated , soft spindle-shaped body of about 1/6 inch. It has a shortantennae and may be distinguished by theabsence of cornicles and has a double orforked tail.

b. Life HistoryAphids reproduce either by laying eggs or bygiving live birth to several young each day.The aphid can overwinter as an immature or asan adult in many different grasses. Wingedforms occur when the host plant conditiondeclines. Winged forms also occur whenRWA are migrating which may occur fromearly Spring to late summer. When wheat andbarley crops mature, RWA will move to later-maturing oats and grasses.

c. Damage RWA inject a toxic saliva into the plant andthen will suck plant sap. Most feeding occurson new growth of the leaf, causing the edgesto curl inward. The first sign of damage is adiscolored plant with tightly curled leaves andlong, white streaks. Tillers may have apurplish or reddish color. Heavily infestedplants can become prostrate or flattened.Damage after heading will appear as twistedor distorted heads caused by the head beingtrapped in the tightly curled leaf.

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d. ControlControl is difficult due to the aphid beingprotected by the curled leaf. Systemic spraysseem to be the better pesticide. Culturalcontrol can be beneficial. Delayed fallplanting can help reduce RWA populations.Like most insect pests, RWA prefer stressedplants. Preference of pesticide use should bechecked each year due to RWA resistance tosome pesticides. Biological control researchand work on resistant plant varieties are underway at many research stations.

E. Major pests of Sugar Beets

1. Sugar beet Root Maggot

a. IdentificationThe adult fly is about 3/8 inch long with ashiny black body and brown legs. The wingsare clear except for a very small area at thebase of the wings.

b. Life HistoryOver winters as a larva (maggot) in soil. InMarch and April maggots move upward withinone to two inches of soil surface and pupate.Adult flies emerge in May, mate and femalesdeposit eggs around base of sugar beet plant.Eggs hatch into maggots which remain allsummer and the following fall and winter.One generation per year.

c. DamageLarvae (maggots) attack small beet plantscausing seedling death and loss of stand.Plants surviving are often severely dwarfedand stunted, and may show secondary rotinfections. Yields are reduced.

d. PesticidesSystemic and non-systemic organophosphatesand carbamates are used to control themaggots. None are persistent but some havehigh mammalian toxicity. Residues are noproblem if label instructions are followed.

e. Pesticide UseAll insecticides should be directed onlytoward larval or maggot control. Hence theyshould be applied to the soil as a 4-6 inchband over the row behind the planter shoe butahead of the press wheel at planting time.Only granular formulations should be used.Granules should not be in direct contact withthe seed. Light incorporation of granules intothe soil is desirable. Granules must havemoisture to become activated.

f. EnvironmentGreatest violation resulting in contaminationof the environment results from a commonmisuse of insecticides. Such misuse includesthe wide-scale indiscriminate use of highlyhazardous insecticides like parathion appliedaerially for control of adults (flies). Controlmeasures should not be directed toward fliesbut rather towards the larvae. By carefullyplacing a lesser amount strategically over therow, more efficient control is obtained at alower cost and with far less pollution.

2. Beet Leafhopper

a. IdentificationThe adult, nearly 1/4 inch long, is slender andtapers posteriorly with the widest point of thebody just behind the metathorax. Color variesfrom gray to greenish yellow. Darkerindividuals have blackish or brownishmarkings on the front wings, head, and thorax.Older nymphs are usually spotted with red andbrown.

b. Life HistoryOverwinter as adults in waste areas in the BigHorn Basin. Some additional ones maymigrate in from the south or southwest in thelate spring or summer. Winter and earlyspring populations are found in variousspecies of wild mustards, Russian thistle andother weed hosts. Eggs hatch and nymphsfeed on weed hosts or move into beet fields.One or more generations per year.

c. DamageMajor damage is mostly to sugar beets.Sucking sap is of lesser importance than beinga vector of the virus causing the disease curlytop in sugar beets. Early symptoms are aclearing of the veins and inward rolling on themargins of young leaves. Then curling of theleaves progresses, veins swell and papillaedevelop on the underside of leaves. Leavesbecome dull, dark green, distorted, thick, andbrittle. Hairy or woolly lateral rootlets,discoloration of alternate concentric circles,general stunting and often death result.

d. PesticidesSee B-543R Control of Field Crop Insects.

e. Pesticide UseIf used early in over wintering areas, use ofinsecticides on a large scale basis treatingentire beet field can be avoided.

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f. EnvironmentAdequate soil moisture is necessary to activatethe granules. They should be applied only tothe soil as a band in order to increaseefficiency and decrease costs and possiblepollution. No aerial application ofinsecticides for adult control throughout beetfields will be necessary.

F. Major Pests of Potatoes

1. Potato Psyllid

a. IdentificationTiny scale-like flat nymphs, margined withwhite fringe. Sometimes called jumping plantlice. Vaguely resemble aphids to the layman.

b. Life HistoryOverwinter as eggs. May be severalgenerations per year.

c. DamageNymphs suck sap from shaded parts offoliage, producing rolled or cupped, yellow orreddish leaves ("psyllid yellows"), killing orstunting the plants, and causing tinymalformed unmarketable potatoes.

d. PesticidesShort residual systemic and non-systemicphosphorus insecticides. Some are availableas granules, other as liquids (E.C.) or wettablepowders (WP).

e. Pesticide UseSystemic granular insecticides should beapplied in bands both sides of the row atplanting time. Approved chemicals in the ECor WP formulations should be applied as afoliar application. Some insecticides may needtwo more applications at two week intervals.

f. EnvironmentShould be used exactly as stated on the label.Soil application of systemic insecticides willbe less detrimental to beneficial and othernon-target organisms.

2. Colorado Potato Beetle

a. Identification (see color illustration PictureSheet No. 9 in appendix). The adults may berecognized by the alternate black and yellowstripes that run lengthwise of the wing covers,five of each color on each wing cover. They

are about 3/8 inch long by 1/4 inch wide andvery convex above. The young larvae aresmall, humpbacked and reddish. The largestfull-grown larvae are as much as 1/2 inchlong, the back arched in almost a semi-circle,with a swollen head and two rows of blackspots on each side of the body.

b. Life HistoryOverwinters as an adult buried in soil anddebris. Eggs are laid in the spring, hatch, andlarvae feed on potato plant foliage. Larvaemay become full grown in one or two weeks.One to two generations per year.

c. DamageBoth adults and larvae have chewingmouthparts. They are voracious feeders,feeding on leaves and often completelyconsuming the leaves.

d. PesticidesCarbamate, organophosphorus and onechlorinated hydrocarbon insecticide(methoxychlor) are approved andrecommended. Most are not too toxic orpersistent. With proper usage there should beno residue problem.

e. Pesticide UseSystemics should be applied as a side dress atplanting time. Others may be applied as foliarapplication, preferably shortly after eggshatch. A second application might benecessary.

f. EnvironmentThe more dense the foliage, the higher thevolume of spray in gallons per acre should be.Non-target organisms are not too likely to beinvolved in potato fields in Wyoming, at leastnot of any consequence.

3. Potato Flea Beetle

a. Identification (see color illustration PictureSheet No. 9 in appendix). Adults are smallbeetles, about 1/16 inch long and nearly auniform black in color. They have enlargedhind legs and jump vigorously when disturbed.The larvae are mostly whitish, slender,delicate, cylindrical worms from 1/8 to 1/3inch long, with tiny legs and brownish heads.

b. Life HistoryUsually overwinter in the adult stage,hibernating under leaves, grass, or trash aboutfield margins, ditch banks, fence rows or

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margins of woods. One or two generationsper year.

c. DamageFoliage may be eaten badly enough to causeplants to die. Cause very small, rounded orirregular holes eaten through or into the leaf,so leaves look like they've been peppered withfine shot. These holes provide openings fordisease organisms. The potato flea beetlespreads early potato blight.

d. PesticidesCarbamates and systemic or non-systemicorganophosphorus insecticides. Systemicsmay be applied as granules.

e. Pesticide UseSystemic granular disulfoton or phorate

should be applied banded on each side of therow at planting time. Most other insecticidesare applied as foliar application.

f. EnvironmentIf carefully applied according to label, thereshould be no detrimental effects on theenvironment.

APPENDIX

PICTURE SHEET NO. 4 - Corn Insects Above GroundPICTURE SHEET NO. 5 - Corn Insects Below GroundPICTURE SHEET NO. 7 - Common Small Grain InsectsPICTURE SHEET NO. 8 - Common Forage Legume InsectsPICTURE SHEET NO. 9 - Common Vegetable Insects

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