A Guide for Scouting Insects of Field Corn

in the Mid-Southern U.S.

Written and compiled by Scott Akin, AssistantExtension and Research Professor, University ofArkansas Division of Agriculture.

Contributors: • Chris Daves, Former Assistant ExtensionProfessor, Mississippi State University

• Scott Stewart, Extension EntomologyProfessor, The University of TennesseeExtension

• Glenn Studebaker, Associate Extension andResearch Professor, University of ArkansasDivision of Agriculture

• Angus Catchot, Associate ExtensionProfessor, Mississippi State University

• Kelly Tindall, Former Assistant ResearchProfessor, University of Missouri

• Don Cook, Assistant Research Professor, Mississippi State University

• Jeff Gore, Assistant Research Professor,Mississippi State University

• Gus Lorenz, Extension Entomology Professor,University of Arkansas Division of Agriculture

• Roger Leonard, Former Professor ofEntomology, LSU Ag Center

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . 1

Relative Efficacy of Bt Corn Products . . . 4

Crop Stages: Planting, Emergenceand Seedling . . . . . . . . . . . . . . . . . . . . . . 6

Crop Stage: Whorl . . . . . . . . . . . . . . . . . . 20

Crop Stage: Pre-Tassel to Black Layer . . 28

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Photo Credits

1,9,10,11,14,22,23,26,27,39,40,41,42,contents,cover – Scott Akin, University of Arkansas

2,3,5,37 – Ric Bessin, University of Kentucky

15,38 – Angus Catchot, Mississippi State University

6,7,18,19,24,47,52,53 – Chris Daves, Mississippi State University

4,8 – Marlin Rice, Formerly Iowa State University

17 – Blake Layton, Mississippi State University

21 – Roger Leonard, Louisiana State University

12,13,16,20,25,28,29,30,31,32,33,34,36,43,45,46,48,49,50,51,54,55 –Scott Stewart, University of Tennessee

35,44 – Glenn Studebaker, University of Arkansas

56 – Kelly Tindall, University of Missouri

The information given herein is for educational purposes only. Reference tocommercial products or trade names is made with the understanding that nodiscrimination is intended and no endorsement by the Arkansas CooperativeExtension Service is implied.

Acknowledgment: The authors of thisguide would like to acknowledge theArkansas Corn and Grain Sorghum Boardfor its support of our research andextension efforts, as well as the printing ofthis guide.

Overview

Field corn is among the most important cereal cropsgrown in the world today. Already the dominant cropgrown in the United States, it has recently undergone afurther increase in acreage. This is particularly true in theMid-South, where corn has “cannibalized” acreage ofother crops such as cotton. Although corn may notrequire as many inputs as cotton (e.g., PGRs, defolia-tion, etc.), proper and timely scouting for insect pestscan still be an important component of obtaining favor-able corn yields. The primary goal of scouting any crop,including corn, should be to minimize input costs andcrop damage while maximizing profit for the grower.

Integrated Pest Management (IPM)

Successful and economical control of corn insect pestsrequires the use of multiple control measures – plantingduring recommended windows, using resistant crop varieties and using insecticides judiciously. Successfulin-season components of IPM consist of, but are notlimited to, 1) scouting the crop in a systematic mannerand on a set schedule to identify pests and/or associ-ated injury, 2) implementing control measures when apest population reaches the economic threshold and3) utilizing an effective control measure to manage pests.

Scouting

Field corn should be scouted weekly from emergencethrough black layer. During the first few weeks, fieldsshould be scouted similarly to other crops where arandom walking pattern (e.g., “zigzag”) is used to ensureadequate coverage of the field. Signs of early-season

1

Introduction

insect injury to look for include nonemergence caused byseed-feeding pests, poor vigor (i.e., yellowing, stuntedgrowth, deformed plants) or plants that have been cut offnear the soil line. Insect damage may exhibit a pattern inthe field such as near field edges (e.g., stink bugs) or inpreviously weedy areas (e.g., cutworms). Perhaps even acertain row of each planter pass may sustain soil insectinjury as a result of a clogged in-furrow insecticide appli-cator. Regardless of cause, affected plants should be dugup to identify any pests that may be present and to docu-ment feeding injury to the seed, growing point or roots.Even if rescue treatments do not exist for the particularpest at hand, knowledge of pest history in a given fieldcan be helpful with future management decisions.

As corn plants are well into vegetative growth stages, itwill be less feasible to follow a true “zigzag” pattern in anygiven field, due to the size of the plants. However, coveringadequate portions of the field is still imperative. Generally,four to eight representative areas of the field, dependingon field size, should be scouted during each visit. Addi-tionally, it is important to continue to observe field bordersfor “edge pests” (e.g., stink bugs, grasshoppers).

Bt Corn in the Mid-South

The term Bt corn has been used generically since thelate 1990s. However, there are Bt traits that exhibit activ-ity against lepidopteran pests (i.e., caterpillars) andthose that do so against corn rootworms. Bt traits withactivity on European corn borers, southwestern cornborers and sugarcane borers have been heavily adoptedin the Midwest as well as the South and play a significantrole in corn IPM at the time of this writing.

In the “Corn Belt” (i.e., the midwestern United States),transgenic corn hybrids that contain Bt genes expressing“rootworm proteins” (e.g., Cry3Bb) are used extensivelyfor control of both northern and western corn rootworms.That said, these pests rarely occur in the Mid-South, with

2

the exception of the southern corn rootworm. Bt cornhybrids containing the rootworm-active traits have littlevalue in the Mid-South because current proteins thatare effective in controlling western and northern cornrootworm have little activity against southern corn root-worm. Therefore, Bt corn hybrids with the greatest valuein the Mid-South are generally those with activity againstlepidopteran pests only.

For resistance management strategy, a refuge area ofnon-Bt corn must be planted when using Bt corn hybrids.This guide will not go into specifics with respect to refugerequirements, because these requirements may varyconsiderably, depending on geographical location andwhich Bt traits are being used, and may change overtime. It is recommended that you consult the licensingagreement that comes with the Bt hybrids selected forplanting for a given season.

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Insect injury on Bt corn (left) and non-Bt corn (right)

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4

Relat ive Ef f icacy of

Originally published in the 2011 Alabama Pesticide Handbook (www.aces.edu /publications/),based on input from the Southern Corn Insect Working Group. Most of these products aremarketed as stacks with herbicide resistance traits. Rankings are meant to be relative.

Traits/brandsPrimary

target pests

Cornborercomplex(stalk)

Blackcutworm(seedling)*

Cornearworm(ear)*

Agrisure CB/LL Corn borers Excellent Poor Fair

Herculex ICorn borers,

FAW,cutworm

Excellent Good Poor

YieldGardVT Triple (VT3)

Corn borers,rootworm Excellent Poor Fair

Herculex XTRA(HXX)

Corn borers,FAW,

cutworm,rootworm

Excellent Good Poor

Genuity VT Triple Pro(GENVT3P)

Corn borers,CEW, FAW,rootworm

Excellent Poor Good-VeryGood

Genuity or DowAgroSciencesSmartStax

(GENSS or SSX)

Corn borers,CEW, FAW,cutworm,rootworm

Excellent Good Very Good

AgrisureViptera 3110

Corn borers,CEW, FAW,cutworm

Excellent Good Excellent

AgrisureViptera 3111

Corn borers,CEW, FAW,cutworm,rootworm

Excellent Good Excellent

Genuity VTDouble Pro(GENVT2P)

Corn borers,CEW, FAW Excellent Poor Good-Very

Good

AgrisureCB/LL/RW

Corn borers,rootworm Excellent Poor Fair

Optimum Intrasect

Corn borers,FAW,

cutworms,LCSB

Excellent Good Fair-Good

Agrisure 3000GT

Corn borers,rootworm

Excellent Poor Fair

5

Selected Bt Corn Products

*Control of target pests by Bt crops is often dependent on the size of the target pest larvawhen it first feeds on Bt toxins. Thus, a product rated as “Excellent” may sustain somedamage if larvae are able to attain significant size by feeding on alternate hosts (i.e.,weeds) before moving onto the plants.

Primarytarget pests

Fall armyworm(whorl)*

Western corn rootworm

(roots)

Lessercornstalk borer

Corn borers Good None Good

Corn borers,FAW,

cutwormVery Good None Very Good

Corn borers,rootworm Good Excellent Good

Corn borers,FAW,

cutworm,rootworm

Very Good Excellent Very Good

Corn borers,CEW, FAW,rootworm

Excellent Excellent Very Good

Corn borers,CEW, FAW,cutworm,rootworm

Excellent Excellent Very Good

Corn borers,CEW, FAW,cutworm

Excellent None Good

Corn borers,CEW, FAW,cutworm,rootworm

Excellent Fair-Good Good

Corn borers,CEW, FAW Excellent None Very Good

Corn borers,rootworm Good Fair-Good Good

Corn borers,FAW,

cutworms,LCSB

Very Good None Very Good

Corn borers,rootworm

Good Fair-Good Good

6

Insects attacking plants at or beneath the soil surface cancause significant damage to germinating seed and/orseedling plants. Although many of these insects cancause injury to older plants, seedling corn is significantlymore vulnerable.

Two important factors to be considered when managingearly season corn pests are (1) preserving targeted plantpopulations and (2) protecting overall plant health ofsurviving plants. Rescue treatments are rarely an optionor may be only marginally effective against soil pests.As a result, in-season scouting is generally not recom-mended for many of these pests. However, finding thesepests in your fields may help provide a history of whatpests may cause problems in the future.

Preventative insecticides, such as seed treatments orsoil-applied insecticides, are the most effective optionsfor control in most cases and are especially justifiedwhen the probability of soil insect infestation is high. Theadoption of reduced tillage systems and use of fieldswith a history of soil insect infestations are risk factorsthat generally justify the use of preventative insecticides.Delayed application or poor performance of preemer-gence herbicides may also increase the likelihood ofsoil/seedling insect pests.

Seedcorn Maggot

The seedcorn maggot can be found on many host cropsas well as corn. The adults are flies that often areattracted to soil that has recently been disturbed byplowing or cultivation. The adult female deposits eggs, upto 100 over a three- to four-week period, in soils that areabundant in organic matter. These pests are commonlyassociated with cool, wet weather and early planting.Adults feed on nectar from flowering plants within or

Crop Stages: Planting, Emergenceand Seedling

around the field, but the immature stage causes the mostdamage to germinating seed and seedling corn plants.Larvae are generally small and yellowish-white in colorwith no legs.

Damage: Maggots feed on germinating seed andseedling plants by tunneling or burrowing. Damagedseed may fail to germinate, or the plant may sustainpoor vigor following emergence. Damaged plants thatemerge will likely appear wilted, stunted or otherwiseunhealthy. If seedcorn maggots are suspected, carefullydig up seed in areas of the field where plant standshave been reduced or failed to emerge. Look closely forsmall, yellowish-colored maggots feeding on the seed orseed contents.

Management: Many insecticide seed treatments arehighly effective against seedcorn maggot. There is norescue treatment for this pest.

White Grubs

The most common white grubs found infesting cornfieldsconsist of May beetles, June beetles and southernmasked chafer. Of these, the annual white grub (a.k.a.southern masked chafer) is not known to cause damageto seedling corn stands. The true white grubs, larvae ofMay and June beetles, can cause significant damage todeveloping corn plants if present in high numbers. Theadult beetles rarely cause economic damage to corn,

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Seedcorn maggots Seedcorn maggotdamage to seed

32

but they do lay theireggs in grass or sod.The grubs areC-shaped and whiteor cream in color withvisible legs. Grubstypically are foundfeeding on roots ofwild grasses andother hosts.

Damage: White grubs damage corn by feeding on thedeveloping root system. Pruned roots usually result instunted plants and even stand loss in heavily infestedfields. Extensive root damage may not kill the plant, butlodging and yield reduction are likely.

Management: Many of the insecticide seed treatmentsand in-furrow insecticides are effective in preventinginjury from these pests.

Japanese Beetle

Grubs of Japanesebeetles are similar towhite grubs, in that theyare white with a brownhead capsule, havechewing mouthparts andmay also curl into a “C”shape when disturbed.Japanese beetle grubs,however, can be identi-fied by the V-shaped

pattern on the underside of the last abdominal segment.Japanese beetles undergo one generation per year andoverwinter as third instar larvae in the soil below the frostline. As soil temperatures warm in the spring, the larvaemove closer to the soil surface to pupate and finallyemerge as adults to find hosts and to mate.

8

Japanese beetle grub

5

White grub

4

Damage: As grubs, Japanese beetles feed on roots,reducing the uptake of water and nutrients. As with othersoil insects, this will often go unnoticed until reducedplant growth and development are observed. Heavilyinfested fields may undergo a reduction in plant stand towhere replanting is often required.

Management: While Bt hybrids provide no control ofJapanese beetles, lower rates of most labeled seedtreatments generally provide adequate control of grubs.In-furrow insecticides may also provide acceptablecontrol. As with other soil pests, there is no rescue treatment for the grub of the Japanese beetle.

Southern Corn Rootworm

Although adults of southerncorn rootworm cause littledamage to seedling corn,larvae can cause damage toplants when they feed on thegerminating seeds or thedeveloping root systems.Rootworm larvae are smalland cream-colored with ablack head on one end of thebody and a dark spot on theother end, sometimes appearingto have two heads.

Damage: Plants that havebeen damaged may appearwilted, with the emergingwhorl leaf of plants wiltingfirst. If plants are severelyinjured, death of the plant mayoccur. Carefully inspect wiltedplants for the presence ofrootworm larvae. Carefullyremove plants from the soiland closely inspect the crown ofthe seedling plants just below

Southern cornrootworm

Southern corn rootworm damage

9

7

6

the soil surface. Rootwormlarvae will also tunnelwithin the roots. Damagedplants surviving rootworminfestations will often lodgelater in the growing seasondue to underdeveloped rootsystems. This sometimesresults in what is referred toas “goosenecking” of corn.

Management: Many of the insecticide seed treatmentsare effective in preventing injury from this pest.

Wireworms

Several species of wirewormscan infest field corn in theMid-South. Infestations aretypically observed when fieldshave recently been planted toa grass crop (e.g., pasture) orhave been out of productionfor a period of time. Fieldsfollowing soybean have alsobeen reported as having wire-worm infestations (Akin andStewart, personal observa-tions). However, sandy soilsare also prone to infestations, regardless of the previouscrop. Wireworm larvae are unique, compared to otherinsect pests, in that they mature in two to five years,depending on species. Thus, infested fields may sustainwireworm injury for several consecutive years. Wirewormscan also be found in no-till fields. Bait stations are some-times used prior to planting to determine whether the useof a soil insecticide (e.g., in-furrow) is necessary duringplanting. Wireworm larvae are elongated, slender andyellowish-brown to brown in color. They have a slightlysclerotized (hard and shiny) exterior with prominentbody segments.

10

Wireworm

9

“Goosenecking” of corn

8

Damage: Plant damage is very similar to that of thesouthern corn rootworm, where damaged seedlings willappear wilted and/or severely stunted. Under heavypressure, extensive feeding may cause “deadheart,” acondition where the plant is severely stunted and oftenleads to death.

Management: Many of the insecticide seed treatments(depending on rate) and several in-furrow insecticidescan be effective in preventing injury from this pest.

Lesser Cornstalk Borer

This lepidopteran pest is more likely to occur in sandysoils and under dry conditions. Larvae are slender andgreenish-purple in color and wiggle around violentlywhen disturbed. They also rarely develop to a size over2/3 inch in their final instar.

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Wireworm damage “Deadheart”

1110

Lesser cornstalk borer larva12

Damage: Larvae cause damage to the corn plant byboring into the base of the stem, which can cause dead-heart and ultimately stand reduction if numbers are high.Lesser cornstalk borer often makes silken tubes from thesoil level attached to the plants. Wilting is one of the firstsigns of attack in affected plants, but withering of buds,stunting and plant deformities are common. Plant deathis not uncommon, and infested areas of fields often havea thin stand.

Management: Insecticides applied for suppression oflesser cornstalk borer are usually applied in a granularformulation in the seed furrow or in a band over theseedbed. Liquid formulations can also be applied, butit is important that they be directed to the root zone.Insecticides may be applied when significant stand lossis imminent.

Aphids

Although other species ofaphid may occur in corn,the corn leaf aphid is oftenthe most common aphidobserved. As in other crops,aphids are typically foundfeeding in clusters on theleaves or in the whorl.Beneficial insects usuallyprevent aphid outbreaks,and treatment is seldomwarranted in corn.

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Aphids

14

13Lesser cornstalk borer

Damage: On seedling corn plants, aphids may be foundfeeding in the whorl. Feeding may cause plants to turnyellow or reddish in color. Seedling corn plants underdrought stress are more susceptible to damage. Plantsthat are not under stress and are growing vigorously aretypically not affected.

Scouting and Management: It is rare for aphid infestations to justify treatment. Therefore, there is littleneed to scout specifically for this pest alone. Most seedtreatments will provide adequate control of aphids onseedling plants. Foliar insecticide applications, althoughseldom needed, are also effective. Extension recommen-dations developed in Midwestern states suggest that if50 percent of the plants have more than 100 aphids perplant and plants are under drought stress, treatment maybe justified. If occurring late in the season, control iswarranted if 3 percent or more of the plants have heavilyinfested tassels and upper leaves, plants are under moisture stress and the population is increasing.

Slugs

Slugs, although not insects,cause damage to cornprimarily by feeding on leafor stem tissue, particularlyto seedling plants. Due totheir affinity for plant resi-due, slugs tend to be moreproblematic in fields thathave undergone little or no tillage. Unwanted vegetationthat emerges in the spring can provide a suitable foodsource for slugs to thrive before crops emerge. Also, ifplanting occurs too soon following herbicide burndown inthe spring, slugs may move from dying weeds onto thecorn stand. Having a sufficient vegetation-free periodprior to crop emergence is imperative for corn seedlings,with regards to slugs as well as other pests. Saturatedsoils or other conditions that favor slow plant growthincrease the likelihood of economic damage from slugs.

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Slug

15

Damage: Because they are nocturnal in nature, slugscan be difficult to detect during the day. However, slugsproduce excessive levels of slime, so trails may be visi-ble on leaf tissue. Symptoms of feeding by slugs can varydepending on the stage of the crop. If feeding occurs onsmall corn, the plant will likely put on new leaves due tothe growing point being below ground. Currently, notreatment threshold exists for slugs; therefore, fieldsshould be treated on a field-by-field basis.

Management: Because slugs and snails are not classified as insects, traditional insecticides are generallynot effective. Certain baits that contain the active ingredi-ent metaldehyde are labeled for control of slugs. If baitsare used, labeled use rates as well as adequate cover-age are necessary to attain control. The best method forcontrol of slugs is prevention. Prior to planting, vegeta-tion removal (e.g., tillage) can reduce habitat for slugs,subsequently reducing future slug populations. However,these practices may not be in line with desired growerpractices, and it may be difficult to make managementdecisions to prevent sporadic pests such as these.Contact your county agent or state extension entomolo-gist for assistance with potential management options.

Billbugs

Several species of billbug can be found incorn. Billbugs areweevils, and the adultsrange anywhere from1/3 to 1/2 inch in length.These insects may begray or brown in colorand are usually coveredwith soil or dust, often

making the insect difficult to see. Several species ofnutsedge (i.e., Cyperus spp.) serve as alternative hostsfor this pest. Therefore, controlling this weed is oftenrecommended when trying to manage billbugs.

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Billbug

16

Damage: Plants showing symptoms may appear wiltedor stunted. These plants are more susceptible to droughtstress and other environmental stresses that affect plantgrowth. Damaged plants will often have smaller ears,depending on the time of the infestation. Leaf feeding byadults appears as a transverse row of oblong holes.When the growing point of the seedling is injured, exces-sive tillering or death of the plant may occur. The poten-tial for damage is much reduced as plants begin togrow rapidly.

Scouting: When a billbug infestation is suspected,examine seedling plants carefully. Billbug feeding generally occurs on the lower portion of the stem, nearthe base of the plant. In fields where billbug populationsmay be present, special attention should be given to fieldedges bordering fields that were in corn the previous year.

Management: The use of soil insecticides or seed treatments offers some control/suppression of infesta-tions. Foliar insecticides may be warranted depending onthe number of insects present and the amount ofdamage to the crop. Rotation to a non-grass crop canalso be effective in managing year-to-year billbug popu-lations. North Carolina State University recommends atreatment threshold of 5 percent seedling loss in infestedareas with a full plant stand. This threshold may bereduced in fields with marginal plant stands.

Chinch Bugs

Chinch bugs overwinter on wild grass hosts. In thespring, populations migrate to new grass vegetation,including seedling corn. Because chinch bugs aresusceptible to rainfall, this pest typically causes moredamage during dry years. The adult chinch bug isapproximately 1/5 inch long with black and white patcheson the wings. Small nymphs are reddish-orange with awhite band across the back. Later-instar nymphs arebrownish-black with a white band across the back.

15

Damage: Both adults and nymphs damage plants withtheir piercing-sucking mouthparts. Extensive feeding willcause plants to wilt, and some may eventually die. Plantssurviving heavy feeding damage by chinch bugs arestunted and develop slower than unaffected plants.

Control: Soil insecticidesor seed treatments willoften control or suppressthis pest. Foliar insecticidescan be used as a rescuetreatment. When usingfoliar insecticides, groundequipment calibrated todeliver high pressure andhigh volume directed at thebase of the plant willprovide the best control.

Scouting: Look for stunted or wilted plants throughoutthe field. Plants damaged by chinch bugs can have a redor yellowish streaky appearance to the leaves. Chinchbugs are usually found at the base of the plant or behindthe leaf collar. Populations can build to high levels insmall grains such as winter wheat, so it is wise tomonitor fields bordering or adjacent to small grains.

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Chinch bugs

18

Chinch bug adult (left) and nymphs

17

Management: Treat when plants are less than 6 inchestall and when at least 20 percent of plants sampledhave five or more chinch bugs. Seed treatments cansuppress populations, and foliar insecticides are ofteneffective. However, sufficient spray volume is essentialfor good coverage.

Cutworms

While several species ofcutworms are known to attackseedling corn plants, the blackcutworm is the most commonacross the Mid-South. Thefemale moth usually depositsher eggs in low-lying/weedyareas of fields. This pest is alsoassociated with cool weather inthe spring, when it is known toattack plants up to 10 inches tall.

Damage:When temperatures are cool, larvae will be ator near the soil surface and will cut plants off at the soilline. In warmer weather, larvae can be found lower inthe soil boring into small plants. This feeding oftenresults in wilting or death of the plant.

Scouting: Due to their nocturnal nature, cutworms arenot likely to be seen during the light of day. Look forareas that sustain some level of stand loss. This willoften be in low areas of the field or previously floodedareas. Fields with vegetation are likely to be infested withcutworms. Damaged plants will be cut off near the soilline. Older seedlings may be cut, or individual leavesmay be cut from the plant.

Management: Cutworms are rarely a problem in fieldskept free of weeds and vegetation prior to planting. Earlyseedbed preparation will often help prevent cutwormsfrom occurring in these fields. Vegetation should beremoved with herbicides or tillage at least two to threeweeks prior to planting, which allows time for any

17

Black cutworm

19

cutworms in the field to starve due to lack of food. Ifvegetation is still present at planting, a pyrethroid can bebanded behind the planter. For populations detectedafter emergence, foliar applications are typically effective,assuming infestations are detected early and beforesignificant stand loss occurs. Pyrethroid insecticides areeffective and are typically recommended for controlof cutworms.

Sugarcane Beetles

The sugarcane beetle adultis black and about 1/2 inchlong. This pest can besporadic and unpredictable inoccurrence. Historically,some fields are more proneto infestation than others.

Damage: The adult stage causes significant damage.They bore into the soil at the base of the plant and usetheir chewing mouthparts to feed on the stalks just belowthe soil surface, sometimes chewing all the way throughthe stalk. Sugarcane beetle can damage plants up to3 feet tall, and serious infestations can decimate stands.Whorl leaves of damaged plants will begin to wilt, anddeath of the plant may occur. Older plants that aredamaged may lean or appear lodged in the field.

Scouting: Look for a small, round hole (1/2 inch diameter)at the base of the plant, where the beetles burrowedbeneath the soil. Carefully remove the soil and thebase of wilted plants. Look for feeding damage andadult beetles.

Management: Treatment for sugarcane beetles is sometimes difficult, as rescue treatments with foliarinsecticides will often not provide adequate control. Useof in-furrow insecticides and seed treatments can helpreduce the chances of damage. However, some insecti-cide seed treatments may not be as effective as otherswith regards to control of this pest.

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Sugarcane beetle

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Stink Bugs

Stink bugs can, in some cases, cause considerabledamage to seedling corn. These pests have piercing-sucking mouthparts and move about the plant searchingfor feeding sites.

Damage: Plants damaged by stink bugs in the whorlstage may be stunted, produce excessive tillers or turnyellow. If damage occurs to the growing point, death ofthe plant may occur. Often, affected plants tend tosurvive but will not contribute significantly to yield.

Scouting: Stink bugs can be found in the whorl probingthe plant, but they can also be found moving up anddown the stalk or at the base of the plant near the soil.Brown stink bugs are easily overlooked at the base of theplant because they blend in well with the soil and debris.Thoroughly check the base of young plants, the areaaround the base of the plants and under crop residue.

Management: Many insecticides are effective againststink bugs found in corn. However, differences in controlare often noted between brown and green stink bugs,with green stink bugs being typically easier to controlwith labeled pyrethroids than brown stink bugs.

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Southern green stink bug

21

Injury to field corn in the whorl stage can be fairlyconspicuous, particularly when the injury results in lossof leaf tissue. This injury can be identified either byragged and irregular holes or “windowpaning” of cornleaves by various pests or small “shot holes” caused bycorn borers. Previous research suggests that corn isrelatively tolerant to defoliation once in the whorl stage,and treatment with a foliar insecticide at this stage rarelyresults in increased yield. However, feeding by heavy,sustained infestations of defoliating pests may lead todeadheart and subsequent reduced yield. If this is thecase, it is very important to identify the pests causingwhorl damage because of the differences in insecticidesusceptibility among them. Most often, early planting isthe most effective method for management of pests thatfeed in the whorl.

Corn Earworms

Corn earworm is highly polyphagous in nature and thusmay be found in many other crops (e.g., cotton, soybean,sorghum). This pest has various color phases and tendsto have more rigid hairs than armyworms.

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Crop Stage: Whorl

Checking whorl for injury

22

Damage: Early larval stagestypically feed on the leafsurface before moving downinto the whorl. As is normallythe case with lepidopteranpests, as the larvae develop,the amount of feedingincreases with each instar.Damaged whorls appear verytattered and torn.

Fall Armyworms

Fall armyworm larvae aresmoother than cornearworm and can rangefrom grey or brown togreenish in color. Fall army-worm typically has fewerand shorter hairs than thecorn earworm and oftenhas black “domino dots” onthe top of the last abdomi-nal segments. Fall army-worm may also have amore prominent, light-colored inverted “Y” on thehead capsule.

Damage: Early larval stages of this pest will feed on theupper surface of leaf tissue of corn, resulting in “window-paning” (i.e., a translucent lower layer remaining). Laterinstar larvae will completely remove portions of plant

21

Corn earworm

Corn earworms

Fall armyworm

25

24

23

tissue resulting in a tattered appearance on the leavessimilar to injury caused by corn earworm.

22

Windowpaning caused by fallarmyworm larval feeding

Fall armyworms in whorl

Tattered leaves due to fall armyworm feeding

26

27

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Armyworms

Armyworms, sometimes referred to as “true armyworms,”have very little hair. They have four abdominal prolegs(as do all other armyworm species). Larvae often haveblack bands on the prolegs. True armyworms are oftenobserved early in the growing season.

Damage: Damage by true armyworms is similar to thatof fall armyworms – feeding by larger instars results in atattered appearance of leaf tissue. These pests are morelikely to migrate into a cornfield as larvae, in contrast tofall armyworms who migrate into fields as adults andsubsequently lay eggs.

Corn Borers

Corn borers, including the European corn borer (ECB)and the southwestern corn borer (SWCB), can causeeconomic damage in field corn. SWCB, however, is morewidespread across the Mid-South and can cause moresignificant late-season lodging than the ECB. Both cornborer species can easily be distinguished from cornearworm and fall armyworm, not only by their generalappearance but because the borers can “back up” whenprodded, an adaptation of many boring pests; whereas,the corn earworm and fall armyworm cannot. Althoughcorn borers are a significant pest in much of theMid-South, whorl stage corn is normally affected by first-generation borers across the region. Populations thatoccur during the first generation are generally moreisolated. The second generation and perhaps even the

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True armyworm29

third generation (the latter in late-planted corn) aremore likely to cause economic damage. Sugarcaneborer (SCB) is currently more problematic in the lowerMid-South (Louisiana and southern Mississippi) and isdescribed in the following section.

Damage: Until resistance to Bt toxins develops, cornborers will be extremely rare in Bt corn hybrids as theycontain proteins that are active against lepidopteran pests.To date, no resistance to Bt corn has been observed. Innon-Bt corn, however, corn borers commonly causeshot-hole defoliation, but they can also tunnel stalks andeven cause deadheart in whorl-stage corn.

Scouting: For lepidopteran pests that cause defoliationin the whorl stage, it is relatively efficient to conductdestructive samples of a few random plants to identifythe species causing the injury. These samples consist ofpulling whorls and unrolling the leaves while looking for

24

Southwestern corn borer European corn borer

SWCB egg mass

3230

31

33Corn borer pupa

larvae. Fall armyworm and corn earworm typically domore substantial leaf feeding in the whorl than cornborers as their entire larval development takes place inthe whorl, whereas corn borer larvae move into the stalkonce they reach sufficient size to do so.

Management: Insecticide applications are usuallynot warranted for corn earworms or fall armyworms feed-ing in whorls unless populations are high. Early plantingis recommended to avoid heavy infestations of earwormsand other caterpillar pests. Bt corns with activity on Lepidoptera provide excellent control of European andsouthwestern corn borers.

Grasshoppers

Grasshoppers of severalspecies attack corn in theMid-South and may be foundin fields at any stage of corndevelopment. Becausegrasshoppers overwinter aseggs underground in unculti-vated areas, they are typicallyfound causing economicdamage near field edges.Many species of grasshoppershave only one generation peryear, but that single generation

25

Grasshopper

Corn borer damage to leaves

36

35

34

26

can last several weeks, depending on species. Thus,“cycling out” will take a longer period of time compared toother insect pests. Grasshoppers also tend to be more ofa problem following a dry spring.

Damage: All grasshoppers use their chewing mouthpartsto remove foliage from the plant, resulting in a raggedappearance. Under conditions of heavy infestations,entire plants can be denuded.

Scouting:When scouting for grasshoppers, look closelyaround field edges and borders. Both adults and nymphscan cause damage. Nymphs are not as mobile as adults,thus damage may be more restricted to isolated areas ofthe field. Adults, on the other hand, are very mobile, andfeeding damage may not be confined to field edges.Grasshopper feeding gives the plant a very raggedappearance. Damaged areas can be very large, andleaves sometimes appear stripped (only the midribremains intact). However, damage is not limited to theleaves. Grasshoppers can also feed on the stem andreproductive tissues, sometimes even the ear.

Management: Grasshoppers are easily controlled withseveral insecticides. Treat when numbers are high andsignificant defoliation is occurring. Edge treatmentsmay be sufficient to prevent spread to the remainder ofthe field.

Stink Bugs

Stink bugs sometimes cause considerable damage to cornless than 2 feet tall. These pests have piercing-suckingmouthparts and move about the plant searching forfeeding sites. Stink bugs can be found feeding in the whorlof young plants or on developing ears prior to silking.

Damage: Plants damaged by stink bugs in the whorlstage may be stunted, produce excessive tillers or turnyellow. If damage occurs to the growing point, death ofthe plant may occur. Often, affected plants tend tosurvive but will not contribute significantly to yield.

Scouting: Stink bugs can be found in the whorl probingthe plant, but they can also be found moving up anddown the stalk or at the base of the plant near the soil.Brown stink bugs are easily overlooked at the base ofthe plant because they blend in well with the soil anddebris. Thoroughly check the base of young plants, thearea around the base of plants and under crop residuethat may be present.

Management: Many insecticides are effective againststink bugs that can be found in corn. However, differ-ences in control are often noted between brown andgreen stink bugs, with green stink bugs being typicallyeasier to control with labeled pyrethroids than brownstink bugs. Adequate spray volume, however, is recom-mended in order for the insecticide to penetrate thecanopy of taller corn.

27

Brown stink bug

37

Stink Bugs

Stink bugs can damage corn from prior to silking throughkernel development.

Damage: Stink bugs probe plants with their beak-likemouthpart and inject enzymes into the plant tissuebefore removing plant juices. Significant ear damage islikely when ears are less than 3/4 inch long. Plantsdamaged during early ear development may result inwhat is referred to as “cow-horned” ears, resulting in totalear loss for that given plant.

Scouting: Scouting for stink bugs should begin beforean ear is visible on the plant. At this stage, scout for stinkbugs up and down the stalk, especially in the ear zone.These pests can usually be found, if present, probing thestalk searching for the developing ear. Stink bug infesta-tion will normally begin on field borders. They also tendto hide and will move or fly when disturbed or threatened.Thus, when scouting for stink bugs, approach the areawith care.

Management: Many insecticides are effective againststink bugs that are common in corn. However, differ-ences in control are often noted between brown and

28

Crop Stage: Pre-Tassel to Black Layer

Stink bug damage

38

29

Brown stink bug nymph

Brown stink bug adult

39

40

Southern green stink bug nymph

Southern green stinkbug adult

42

41

green stink bugs, with green stink bugs being typicallyeasier to control with labeled pyrethroids than brown.Adequate spray volume, however, is recommended inorder for the insecticide to penetrate the canopy oftaller corn.

Corn Borers (Southwestern, European and Sugarcane)

The corn borer complex listed in this guide can be foundthroughout the Mid-South. However, the sugarcane borer(SCB) is generally confined to Louisiana and SouthernMississippi at the time of this writing. The larvae of allthree species have similar feeding habits in that they willtunnel into the plant and feed on the pith in the stalk.

30

Southwestern corn borer larvae

Southwestern corn borer adult

European corn borer

Sugarcane borer

47

46

45

43 44

Pheromones are available formonitoring adult populationsof southwestern corn borer(SWCB) and to some extentEuropean corn borer (ECB),but not for the SCB. BothSWCB and SCB larvae canbe observed in two forms,summer and winter. In SWCB,the summer form is white withblack spots, while the winterform is creamy-white with barely-visible spots. The SCBis typically white with a brown head, and the summerform has brown spots on each body segment. The winterform of SCB lacks spots altogether.

Damage: Corn borerscause plant injury by leaffeeding, stalk tunnelingand ear feeding. Tunnelingreduces translocation ofnutrients through theplant, and stalks that aresignificantly weakenedmay break over (lodge).Most yield loss, however,is related to lodging ofplants, resulting in failureto pick up those plantswith a combine at harvest.Additionally, larvae of

second or third generation SWCB will girdle the base ofthe plant in preparation for overwintering. This damagecan also cause plants to lodge.

Scouting: In fields planted to non-Bt hybrids only, scoutfor egg masses or small larvae. When scouting for cornborer eggs in tasseling corn, look from eye level to belowthe ear for eggs on both the top and bottom of theleaves. Egg masses are relatively small, but will typicallybe at or near the midrib of the leaf. SWCB eggs morethan a day old will be white with three red “candy-stripes”

Corn borer trap

Corn borer damage

31

48

49

across each egg, while ECBeggs will not. If eggs areless than one to two daysold, SWCB eggs will nothave the candy-stripes. Themain characteristic ofSWCB eggs compared toECB, however, is thatSWCB eggs will usually belaid in clusters of 2 to 5 while ECB typically lays eggs in clusters of 15 or more.

Pheromone traps canbe effective for moni-toring populations ofSWCB. A sharpincrease or “spike” inmoth captures shouldnot be a cue for anautomatic insecticideapplication but intensi-fied scouting. Addi-tionally, there is often

a 7- to 10-day delay in finding eggs following a spike inmoth numbers, as mating, oviposition and egg hatchneed to occur for larvae to be present. Once eggs hatch(4 to 6 days after oviposition), they will feed on foliagefor 7 to 10 days, after which time they will tunnel intothe stalk.

Foliar insecticides must be applied before larvae reachsufficient size to bore into the stalk. Treatment decisionsin non-Bt corn can sometimes be made based on thenumber of SWCB moths in traps surrounding a givenfield. However, this number and how it relates to treat-ment decisions is generation dependent and dependentupon the time of the season as well as the maturity ofthe crop. For example, 50 moths captured in a givenweek is not a high number for the second generation,but it is high for the first generation of SWCB. For early-planted corn (recommended for non-Bt hybrids), thethird generation typically emerges too late to be ofeconomic significance.

32

Corn borers caught in trap

SWCB eggs

52

50 51

Management: Transgenic hybrids with Bt traits activeagainst caterpillar pests provide very effective control forall corn borer species. The use of Bt corn hybrids on atleast some acreage is recommended, especially in areaswith a history of corn borer problems. For non-Bt corn,planting earlier in the season will help avoid late-seasonpressure from corn borers. Tillage prior to spring mothemergence can reduce the overall overwintering popula-tions, but even well-tilled fields can still be heavilyinfested by neighboring fields. For SWCB, apply insecti-cides when larvae or egg masses are present on25 percent or more of the plants. For ECB, apply insecti-cides when larvae or egg masses are present on50 percent or more of the plants. For SCB, 10 to20 percent infested plants is the recommended thresholdin Louisiana.

Ear-Feeding Pests(Corn Earworm/Fall Armyworm)

Ear-feeding caterpillars,such as fall armyworm andcorn earworm, arecommonly found feeding ondeveloping kernels in theear, especially in later-planted corn. Control ofthese pests in field corn isgenerally not recommendeddue to the extremely highnumber of insecticide appli-cations that would berequired to attain control.This is due to the prolongedperiod of silking coupled withthe fact that larvae are bettercontrolled prior to entering theear. The original Bt cornhybrids are not very effective for controlling cornearworm or fall armyworm in the ear. Newer Bt cornhybrids that contain novel and/or multiple Lepidoptera-active Bt proteins may result in enhanced control of

33

Corn earworm damage

Corn earworm

54

53

these pests (see chart on pages 4 and 5). In general,these traits have considerably more activity on cornearworm and fall armyworm.

Scouting: As it is not economically viable to treat caterpillar pests in the ear, scouting specifically for thesepests is generally not recommended.

Japanese Beetle

Adults of Japanesebeetle are approximately1/2 inch in length and aremetallic green withbronze/copper-coloredwing covers. Adults alsotypically have five tufts ofwhite hair that protrudefrom under the wingcovers on each side of the abdomen and two tufts on therear of the abdomen.

Damage: Although Japanese beetles are of littleeconomic significance, adults can cause some defolia-tion. They can also feed on corn silks, which can impactthe pollination process. This, in turn, may result inreduced kernel number on the ear.

Scouting: In areas where Japanese beetles have beenproblematic, traps can be useful for detecting adult beetleemergence and for indicating when scouting for adultsshould be increased. Checking entire fields is necessaryto determine accurate infestation levels, although infesta-tions are often worse along field edges. Thresholdsvary by state, so seek guidance from state extensionpersonnel when addressing treatment decisions.

Management: Adult Japanese beetles are highly mobile,and controlling the immature stage of this pest (withpreventative, at-plant insecticides) does not guaranteeprevention of adult numbers later in the season. Although

34

Japanese beetle

55

several foliar insecticides are labeled for controlling adultJapanese beetles in corn, injury level, population density,yield potential and insecticide cost should all be factorsin deciding whether to treat.

Moodna bisinuella

Moodna bisinuella is a relatively new pest of corn in theUnited States. This pest is native to Central America andarrived in North Carolina on gamagrass from Mexico.First reported in the U.S. in 1985, this pest has beendocumented more recently in south Texas, Louisiana,Mississippi and Georgia.

Damage: Larvae can be found late in the season,usually beyond dent stage, feeding on kernels. Larvalfeeding from this pest is unique in that a frass (excre-ment) trail is created between the rows of kernels wherefeeding takes place. Pupae of this pest are about1/4 inch long and can sometimes be found on the husk.

Scouting: As it is not economically viable to treat caterpillar pests in the ear, scouting is generallynot recommended.

Management: Little is known about this invasive pest atthe time of this writing. Currently, available Bt corns usedin the Mid-South have little activity against M. bisinuella.

35

Moodna bisinuella56

AAphids, 12-13Armyworms, 23

BBillbugs, 14-15Brown stink bug, 19, 26-27

CChinch bugs, 15-17Corn borers, 2, 9, 21,

23-25, 30-33Corn earworms, 4, 20-21,

33Corn leaf aphid, 12Corn rootworms, 2Cutworms, 2, 4,17-18

EEar-feeding pests, 33 European corn borer, 2, 23

FFall armyworms, 3, 5,

21-22, 33

GGrasshoppers, 2, 25-26

JJapanese beetle, 8-9,

34-35

LLesser cornstalk borer,

11-12

MMoodna bisinuella, 35

SSeedcorn maggot, 6-7Slugs, 13-14Southwestern corn borer,

2, 23, 25Southern corn rootworm,

3, 9-10Southern green stinkbug

19Stink bugs, 2, 19, 26-27,

28-29, 30-31Sugarcane beetles, 18Sugarcane corn borer, 2,

30

TTrue armyworm, 23

WWhite grubs, 7-8Wireworms, 10-11Western corn rootworm,

2, 5

Index

36

The Division of Agriculture offers its programs to all eligiblepersons regardless of race, color, national origin, religion,gender, age, disability, marital or veteran status, or any otherlegally protected status, and is an Affirmative Action/EqualOpportunity Employer.