corn - crop protection

8/13/2019 Corn - crop protection

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4 CORN INSECT PESTS: A DIAGNOSTIC GUIDE

Seedcorn maggot

Seedcorn beetles

Wireworms

White grubs

Corn flea beetle

Billbugs

Thrips

Grape colaspis

Black cutworm

Sod webworm

Southern corn leaf beetle

Chinch bug

Armyworm

Stalk borer

Grasshoppers

European corn borer(1st gen.)

*Southwestern corn borer(1st gen.)

Corn rootworms

Fall armyworm

Corn earworm

Corn leaf aphid

European corn borer (2nd/3rd gen.)

*Southwestern corn borer (2nd/3rd gen.)

larvaeadults

larvae adults

APR MAY JUN JUL AUG SEP

The most injurious insects in corn are listed in boldface type.

*Southwestern corn borer is an economic pest primarily in southeasternMissouri and the southern quarter of Illinois.

This time line is estimated for central Missouriand south-central Illinois. Adjust time line asshown for other regions.

Use time line

7-10 days

5-7 days

5-10 days

Time line for corn insects in central Missour i

and south-central Illinois

GarryBrix


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Knee-high to tasseling corn (V8 to VT)Leaf t issue rem oved

Chunk s of plant tissue removed f rom leaf margins,

or ragged holes in leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 28 Stalk bo rer Grasshoppers

Armyworm Corn earworm Fall armyworm

Small, circular holes or elongated lesions in leaves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 European corn borer

Southwestern corn borer

Stalks malform ed: Lodging or growing upw ard in a gooseneck shape . . . . . . . . . . . . . . . . . . . . 38 Corn rootworm larvae

Holes bored in stalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Stalk borer

European corn borer


Tasseling to corn matur ity (VT to R6)Leaf t issue rem oved

Chunk s of plant tissue removed f rom leaf margins,

or ragged holes in leaves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Armyworm

Fall armyworm

Grasshoppers

Small, circular holes or elon gated lesions in leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 European corn borer


Corn rootworm beetle (esp. western)

Stalks malform ed or brok en

Lodging or growing upward in a gooseneck shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Corn rootworm larvaeStalks broken . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

European corn borer


Tassels dam aged

Tassels brok en . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 European corn borer

Tassels eaten (in whorl) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Fall armyworm

Tassels discolored . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Corn leaf aph id

Silks clipped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Grasshoppers Japanese beetle Corn roo tworm adults Yellow woo llybear

Corn earworm

Ear damage

Large chunks of kernels removed, often at blister and m ilk stages. . . . . . . . . . . . . . . . . . . . 47 Grasshoppers

Tunneling or chewing damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Fall armyworm

European corn borer

Corn earworm

Ear drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 European corn borer


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7Corn planting to full emergence

(up to V2)

OVERVIEW

From planting to emergence, look for:

Gaps or skips in the row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 7

seedlings pulled up and eaten seeds bored into or completely hollowed out

SYMPTOMS

Gaps or skips in the rowSeedlings pulled up and eaten

When gaps or skips are found in a row of emerging corn

seedlings, first rule out planter malfunction, pesticide misapplication,and seedling diseases. Check to see if seedlings have been pulledup and eaten by birds or rodents. Birds (often red-winged blackbirds, or geese if near a waterway) leave clues in the rows such asbeak marks, tracks, or droppings. Rodents frequently leave a smallmound of soil to one side of the row where the seed or seedlingwas dug up.

Seeds bored int o or hollow ed out

Dig up ungerminated seed to pinpoint the cause of poor emergence. If seeds are bored into or completely hollowed out, checkfor the following three insect pests:

Seedcorn maggot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 8 Seedcorn beetles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Wireworms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

MaureenO

Day

Un

ivers

ityo

fMissouri

Gaps in the stand. Exam ine field for clu essuch as patt ern s of damage or n onemergence. D ig up seeds or damaged seedl i ngsto assess cause of i njur y.

Seedl i ngs upr ooted by bi r ds. Bi r ds leaveclu es such as beak mar ks along the row.Rodent s may l eave small mounds of soil .


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Seedcorn m aggot consum ing i nt er i or ofcorn kern el. T hi s pest may be most pr oblemati c in earl y-plan ted fields hi gh inorgani c matter.

IowaStateUniversity

p

hotosbyMarlinRice

Seedcorn Maggot

Appearance / Life cycleSeedcorn maggots taper toward the front end and are 14 inch long,

yellow-white, legless and apparently headless. Maggots burrow into theseed, and seeds either fail to germinate or produce weak seedlings. Theadults are 14 inch long, gray-brown in color, and resemble small house flies.The maggot life cycle requires 3 weeks at temperatures above 50 degrees F.Although there are three to five generations each year, later generations areof little economic importance.

ManagementThe egg-laying adults (flies) are attracted to moist soils high in organic

matter or decaying residues. Insecticide seed treatments should be considered for early-planted cornfields in which a large amount of manure orspring vegetation has been recently incorporated. Damage can be moresevere when cool, wet spring weather delays seedling emergence. No rescuetreatment exists. If spot replanting, use a seed treatment if the soil temperature is expected to remain cool.

Fields most likely to sustain injuryEarly-planted fields high in organic matter or crop residue are the most

vulnerable, especially during prolonged periods of cool, wet weather.

DistributionStand reduction due to seedcorn maggot is usually more uniform than

the spotty damage typical of wireworms.

IncidenceApril and May

Seedcorn Beetles

Appearance / Life cycleTwo types of seedcorn beetles cause the same injury symptoms and are

both about 13 inch long. The seedcorn beetle is dark brown with two darker

stripes on the wing covers; the slender seedcorn beetle is reddish brown incolor and slightly more elongated and narrow. These beetles are opportunistic feeders and will attack germinating corn when insect prey is in shortsupply. Seedcorn beetles scurry across the soil surface and are rarely foundon plants.

Slender seedcorn beetl e (t op) and seedcorn Managementbeetl e (bottom) . Both beetl es ar e about 13in ch long. No rescue treatment exists. If spot replanting, use a seed treatment con

taining an insecticide if the soil temperature is expected to remain cool.

Fields most likely to sustain injuryNo-till fields in areas where the seed furrow is not completely closed are


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9CORN PLANTING TO FULL EMERGENCE (UP TO V2)

susceptible to seedcorn beetle damage. The potential for injury is higher

when cool, wet spring weather delays seedling emergence.Confusing look-alikes

Many species of beneficial ground beetles resemble seedcorn beetles inshape and color but are generally larger.

IncidenceApril and May

WirewormsWireworm larvae feed primarily on germinating seeds and roots and may spend

3 to 6 years in the soil.

Appearance / Life cycleWireworms are insect larvae that become small to medium-sized beetles.

Adult wireworms, when placed on their backs, can flip themselves uprightwith an audible click and are known as click beetles. Because of their long

Wi reworm adultlife cycles, a range of larval ages and sizes can be found in an infested field. or cli ck beetl e.Larvae are segmented, shiny and wirelike, yellow to reddish brown, andfrom 12 to 112 inches long. Wireworms are attracted to the carbon dioxidefrom germinating seeds and are active in the root zone (upper 2 to 6 inches)when the soil temperature is from 55 to 75 degrees F. As the season progresses and the soil becomes hot and dry, wireworms migrate downward in

the soil so that it may be difficult to find them during a dry summer, even inheavily infested cornfields.

DamageGaps in the stand or nonuniform growth may result from wireworms

tunneling into germinating seeds. However, wireworms can also weaken orkill emerged seedlings by

Feeding on tender young roots Boring into the base of corn plants below ground Drilling upward into stalks of larger corn plantsInjured seedlings often are stunted and wilt as drier soil conditions

develop; leaves are sometimes tinged with blue or purple at the tips. Severe

wilting can be expressed as dead heart, in which the center leaves of aplant are dying. Dead heart is caused by damage to the growing point andmay be accompanied by stunting and excessive tillering.

Most of the damage to corn in Missouri and Illinois is caused by speciesof wireworms belonging to the genusMelanotus.

ManagementNo postemergence treatment is available, so management strategies must

be implemented at planting or before. The need for control is based onfield history or the results from wireworm solar bait stations. The solar-baiting technique makes it possible to estimate before planting whether awireworm population will be economically damaging. Two to three weeks

Armon

Keas

ter

Lee

Jen

kins

Lee

Jen

kins

Wir eworm (above), the damagi ng stage.W i r eworms feed on seeds and young r oots(below); t hey also bore in to the base of cor nbelow gr ound.


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Al though plants typically sur vive this dam- mixture of equal parts untreatedage, they may be stunted. corn and wheat at the bottom of

the station. Mound a soildome over the covered bait to

serve as a solar collector and pre- Cr oss secti on of a solar bai t stat ion forvent standing water. Cover with detecti ng pr esence of wi r eworms.

an 18-inch-square sheet of blackplastic topped with a 1-yard-square sheet of clear plastic, and cover edges

before the anticipated planting

date, establish 5 to 10 bait stations per field (more if the field islarger than 30 acres). Any grassyspots in the field and any areaswhere wireworms caused injurylast season should be baited. Digeach bait station 2 to 3 inchesdeep and 6 to 9 inches wide atthe soil surface. Bury 12 cup of a

UniversityofIllinois

ArmonKeaster

ScottKeasterandGarryBrix

Wir eworm dr il li ng in older cor n plants.

with soil to hold the plastic sheets down. A few days before planting, dig upand sift through the soil and germinated grain to determine the number ofwireworm larvae found within each station. The economic threshold is anaverage of one wireworm per bait station within the baited field.

Management options if you find wireworms in the bait stations: Seed treatment containing insecticide (if wireworms are present but

average less than the economic threshold). Seed treatment protectsonly the seed and will not protect the seedling following germination.

Solar bait stat ion install ed in field. Sur vey

Application of banded or in-furrow insecticide at planting time (if baitflags help m ar k the spot f or inspecti ontrap numbers average one or more wireworms per trap).before plant in g.

Fields most likely to sustain injuryFemale click beetles lay eggs mostly near the roots of grasses. Therefore,

wireworm injury is likely to be most severe in first- and second-year cornfollowing long-standing meadows, pastures, and small grains. Cornfieldswith chronic infestations that are left uncontrolled for several years may alsosuffer heavy damage. Porous, well-drained loam soils are more likely to beinfested with wireworms than are heavy clay soils.

DistributionWireworm populations are not uniformly distributed, so infestations

often appear in hot spots within the field. Stunted, wilted, or dead cornplants may be found next to healthy plants.

Confusing look-alikesGround beetle larvae are about the same shape and size as some

species of wireworms, but they have two large, curved jaws and two softprojections on the tail end.

IncidenceWireworm larvae are found from April through early June; adult click

beetles are found from mid-May through June.


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11Emergence to knee-high corn

(VE to V8)

OVERVIEW

From emergence to the knee-high stage, look for:

Stunting or wilt ing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pages 11, 12

stunting overall wilting dead heart

Unnatural growt h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

stem twisting or excessive tillering

Speckled or sandblasted leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

leaves with speckled appearance

Removal of plant tissue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

irregular narrow tracks plants cut off near base chunks of leaves eaten small rounded holes in leaves lacy skeletonized leaves

SYMPTOMS

Stunt ing or w iltingStunt ing of corn plants, sometimes w ith the leaf tips tinged blue

or purple, can be the result of root pruning by several insects.Overall wilting of corn plants can sometimes be observed in conjunction wi th stunting.

Often an affected plant will be only inches from a healthy and

vigorous plant . This patchy, hot spot distribution can help distinguish insect damage from agronomic stresses such as herbicideinjury, phosphorus deficiency, or compaction. Dig up and check forroot pruning, and examine the soil around the root mass for thesepossible culprits:

Wireworms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 9 White grubs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Grape colaspis larva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

(More stunting o r w ilting symptoms onpage 12)Armon

Keas

ter

Armon

Keas

ter

Stun ted corn plan t next t o a healt hy one(above). Patchy distr ibu ti on of wi lt edplan ts (below) i s often a clue that t he cause

is insect f eeding.


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Wil ted cor n plants next t o ri peni ng gr ainfield. Check wi lt ed plan ts near t heir basefor cluster s of chi nch bugs.

D ead heart r esul ti ng

from i njur y to growingpoin t below gr ound.

Char acteri sti c C- shape of whi te grubs(top). Br istles of the tr ue whi te gr ub for ma zi pper on t he raster (bott om) l ocatedon the underside of the last abdominalsegment.

LeeJenkins

ArmonKeaster

LeeJenkins

LauraKabrick

(Stunting or wilting symptoms continued from page 11)

SYMPTOMS

When wilting or stunt ing occurs in localized areas borderingripening small grains, and masses of small, active, reddish or black-and-white sucking bugs are clustered in the soil near the bases ofstressed corn plants, the pest is

Chinch bug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 14

Severe wi lting can be expressed as dead heart , in which thecenter leaves of a plant wilt and die; sometimes the affected leavestake on a blue-green tint before dying. Dead heart is caused by aninsect tunneling through the stalk into the growing point and maybe accompanied by stunting and excessive tillering. The threeprime suspects are

Wireworms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Black cutworm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Older larvae occasionally tunnel into the stalks of largercorn, especially during dry periods.

Stalk borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

White GrubsWhite grubs are the larval form of scarab beetles (June beetles and several species

of chafers). All of the grub species prefer to feed on the roots of grasses, and themajority of eggs are laid in sod and grassy areas of the field. The two types of grubscommonly found in Missouri and Illinois cornfields are true white grubs (June bee-tles or Phyllophaga spp.) and annual grubs.

Life cycleTruewhitegrubshavea3-yearlifecycleandspendtwoconsecutiveseasonspruningrootsandeatingorganicmatterinthesoil.Annualgrubscompleteasinglegenerationeachyear;theyfeedverylittleinthespring.

Diagnostic tipThesetwotypesofgrubscanbedistinguishedfromeachotherbythe

patternofdark,bristlyhairsonthebottomofthetail(calledtheraster). Truewhitegrubshavetwozipperlikeparallelrowsofbristlesontheraster;onannualgrubs,thebristlyhairsarescatteredandhavenopattern.


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13EMERGENCE TO KNEE-HIGH CORN (VE TO V8)

Damage

Truewhitegrubschewoffroots,andthisrootpruningresultsinabove-groundstuntingandwilting(especiallyindrysoils).Leaftipsoccasionallyturnpurplefromthetipsback;lowerleavesareaffectedfirst.Annualwhitegrubscancausesomeinjury,occasionallyresultinginminorstandloss,whengrowingconditionsarenotoptimum.

ManagementAlthoughnoestablishedthresholdexists,twoormoretruewhitegrubs

percubicfootofsoil(asnotedduringatillagepass)maycausestandlossincorn. Norescuetreatmentexists.Consideranin-furrowinsecticidetreatmentifcornisplantedoverpastureorgrassygroundbroughtoutoftheConservationReserveProgram.Forannualgrubs,soilinsecticidesarenotrecommended.

Fields most likely to sustain injuryBecausescarabbeetlesfavorgrassyareasforegglaying,cornfollowing

sodismostatriskforrootpruningbytruewhitegrubs.

IncidenceWhitegrublarvaearefoundfromAprilthroughearlyJune.

Whi te gr ub damage tocorn seedli ng. Root prun

in g results in wi lti ng andstunting.

Grape ColaspisThe grape colaspis has a broad host range, including corn. Although both the

adult beetle and larval stages feed on corn, damage is seldom economically significant.

Appearance / Life cycleTheimmatures(larvae)arealsocalledcloverrootwormsandresemble

miniaturewhitegrubs.Theyarestout,gray-whiteandabout18 inchlong,withlightbrownheadsandthreepairsoftruelegs(nearthehead).Theadultbeetlesaretan-coloredandabout16 inchlong. Thewingcoversappearstripedduetolongitudinalrowsofshallowpits.

Thepartiallygrownlarvaeoverwinter,androotfeedingresumesinMay.Femalesdepositeggs,usuallyinclumpsofabout36,neartherootsofhostplants. Thereisasinglegenerationeachyear.

Lee

Jen

kins

Lee

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kins

Confusing look-alikesGrapecolaspisadultsshouldnotbeconfusedwithnewlyemerged,

palenortherncornrootwormbeetles.Thetancolorwillbesimilar,butgrapecolaspisbeetlescanbedistinguishedbytheirsmallersizeandalsotherowsofshallowpitsthatappeartoformstripesonthewingcovers.

Also,dontconfusethetiny,18-inchgrapecolaspislarvaewithearly-stagewhitegrubs.Grapecolaspislarvaearelessstronglycurved(morecomma-shapedthanC-shaped)andhavesmallbumpsthatbearaclumpofhairsontheundersideoftheabdomen.

DamageGrapecolaspislarvaeprunetheroothairsorgnawnarrow,lengthwise Gr ape colaspis adult and it s feedin g damage

Gr ape colaspis lar vae and pupa(upper r ight ). Root pru ni ng bylar vae produces abovegr oundsymptoms sim i lar to damage bywhi te gru bs.


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Chin ch bug adul ts and nymphs. T hey frequent ly congr egate behi nd leaf sheaths atthe base of cor n pl ants.

photosbyLeeJenkins

ThomasJ.Riley

Chin ch bug inj ur y to corn . T he plant isstunt ed and t he stal k has fai led to elongate,so that leaves appear clustered around t hebase of the plan t.

stripsfromtherootsofcornseedlings.Cornplantsappearpurpleand

stunted,seldomreachingaheightof10inches,andmaywiltonhot,drydays.Adultbeetleschewholesintheleaves,orstriponesurfaceawaytogivea

windowpaneeffect.Thisminordefoliationdoesnotresultineconomicinjurytocorn.

ManagementNoeconomicthresholdforgrapecolaspisinjuryhasbeenestablished,

andnosoilinsecticideislabeledforcontrolofthisinfrequentpestincorn.

Fields most likely to sustain injuryFirst-yearcornfollowingcloverortimothysod,favoriteegg-layingsites

ofgrapecolaspis,aremostsusceptibletofeedingbythelarvae.

Occasionally,cornplantedaftersoybeansoralfalfaisinjuredbylarvalfeeding. Adultsalsofavorpatchesofsmartweedforegglaying,andsoybeanfieldswithheavysmartweedpressuremaybeinfestedwiththelarvaethefollowingspring. Injuryisusuallymoreseverewhenunfavorableweatherslowsthegrowthofseedlingcorn.

DistributionThedamagetypicallyoccursinpatcheswithinafield,becausegrape

colaspiseggsarelaidinlargeclumpsnearthebasesofhostplants.

IncidenceLarvaearefoundinMayandJune;adultsappearinJuneandJuly.

Chinch Bug

Appearance / Life cycleFull-grownadultsare316 inchlong. Chinchbugshaveablackbodyand

whiteforewingswithtwoblackspots.Winglessnymphschangefrombrightredtoblackastheydevelopandhaveawhitebandacrosstheback.Adultsprefertooverwinteratthebaseofwarm-seasonbunchgrassesandthenmigratetosmallgrainsearlyinthespring. Asthesmallgrainsmature,chinchbugsmoveintoadjacentfieldsofmoresucculentcornandsorghum.

Diagnostic tip

Whencrushed,chinchbugsgiveoffadistinctive,mustyodor.

DamageChinchbugsinducewiltingbyremovingplantjuiceswiththeirpiercing-

suckingmouthparts.Injuryisfirstevidentonlowerleaves,whichturnyellowandwilt. Thestalkfailstoelongateproperlyanddamagedplantsbecomestunted,withtheleafsheathsclusteredatthebaseoftheplant.Leavesofstuntedplantsoftenshowyelloworreddishstreakingfromchinchbugfeeding. Youngplantsareoftenkilled,especiallyifdrought-stressed.Heavilydamagedplantsthatsurviveremainstuntedandmayproducesuckers.

Adultsandwinglessnymphsarefoundnearthebaseofthestalk,behind


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leafsheaths,oronthestemandrootsbelowgroundduringdryconditions.

Thepotentialforchinchbugdamageishigherduringhotanddryspringsandearlysummer.

Confusing look-alikesNewlyhatchedreddishchinchbugscanresemblesmall,brightred

soil-dwellingmites,andchinchbugadultscanbemistakenforfalsechinchbugs. Falsechinchbugadultsare18 inchlongandgrayishwithwingsthatareclearandlacktheblackspotsofthechinchbugswingcovers. Falsechinchbugnymphsarebrownishgraywithtinyreddishspotsonthetanabdomen,andtheylackthewhitebandfoundacrossthemiddleofchinchbugnymphs. Falsechinchbugsprefertosucksapfrommustard,pepperweed,shepherds-purse,andotherweeds.Cornisattackedonlywhentheweedhostsbecomeunavailable. Likechinchbug

injury,heavyfeedingbyfalsechinchbugsmaycausewiltingandbrowningoftheouterleafmarginsincorn.

ManagementTreatborderrowsatfirstmigrationiflowerleavesbegintoturnyellow

andwither.Atentativethresholdis10chinchbugsperseedlinguptotheV4stage.

DistributionInfestationsfirstdevelopneartheouter30to40rowsofcornfieldsbor

deringripeningsmallgrains. Anareaofwiltedorstuntedcorngradesintoundamagedplantsatthemarginoftheinfestation.

IncidenceLateMaythroughJune

W il ted plants. If wi lt in g is locali zed nearsmal l gr ains or gr asses, check the base ofplan ts at and below gr ound level for chin chbugs.

Le

eJen

kins

T

homas

J.

Riley

Black CutwormThe black cutworm is by far the most destructive species of the cutworm complex

in corn. However, there are other less common subterranean cutworms that clip orinjure seedlings in the same way as the black cutworm. See box on the claybackedcutworm.

Appearance / Life cycleTheadultmothsaregraywithasmallblackdaggermarkingoneach

forewing. TheblackcutwormdoesnotoverwinterinMissouriorIllinois(exceptoccasionallyinMissourisBootheelregion).Mothsmigratetothe Sixth- in star black cutworm l ar va next to

CornBeltfromcoastalareasoftheGulfofMexicoinearlyspring.Most cli pped stem. Cut ti ng of corn begins when

eggsaredepositedonlow,densevegetation,especiallyearlyseasonlar vae r each t he four th in star.

broadleafweedssuchaschickweedandcurlydock. Thegrayishlarvahasnodistinctmarkingsandispalerontheunderside. Theblackcutwormprogressesthroughsixorsevenlarvalstages(calledinstars),butlarvaemustreachthefourthinstarbeforetheyarelargeenoughtocutseedlingcorn.Thelarvaearenocturnalfeeders,hidinginshallowburrowsorundersoilclodsduringtheday.Althoughthereareseveralgenerationseachyear,onlythefirstgenerationcauseseconomicinjuryincorn.


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Pinhole leaf feeding bythir d-in star or youngercutworm l ar vae.

Signs of black cutworm cutti ng. Plant scan be severed above or below gr ound(above). A cutworm may dr ag a cut plan tin to it s bur r ow and feed on i t l ater.Gent ly di g around wi lt ed or severed plan tsto expose the cul pri t for posi ti ve identi ficati on (below).

JimJarman

JimJarman

LauraKabrick

isabouthalfthediameterofback cles(oneachsegment)outerpaironeachsegment

diameter Damagemaybeeconomic

DavidPinkerton

DavidPinkerton

Identification tips:Black cutworm Dingy cutworm

Grainy,roughskintexture SmoothskintextureFrontinnerpairofdorsaltubercles Allfourofthedorsaltuber-

areapproximatelyequalin

Cutscornatorbelowthesoillevel Leaffeeder;rarelycutscornNotaneconomicproblem

Black cutworm D in gy cutworm

Confusing look-alikesDonotconfusetheblackcutwormwithotherleaf-feedingcutworms

ofminorimportanceorwithcraneflylarvae.Distinguishblackcutwormfromthedingycutwormbyskintextureandthesizeofthetubercles

(dark-pigmentedbumps)oneachsegmentontheback.Thelarva(maggot)ofaspeciesofcraneflycommonlyfoundinwetcornfieldsinearlyMayisaboutthesamelengthandcolorasayoungblackcutworm,butdoesnotinjureplants.Thereareobviousphysicaldistinctions:Black cutworm Crane fly larva

Well-developedheadcapsule Poorlydevelopedhead Notail-endprojections Fleshyprojectionsaround Threepairsoftruelegsbehindthe thetailend

headandfleshyprolegsonthemiddle Leglessandrearsegments

Damage

Signsandsymptomsinclude: Leaffeeding,usuallyconsistingofsmallpinholesandlightmargin feedingbylarvaetoosmalltocutplants(thirdinstarsorsmaller)

Plantscutatorjustabovethesoilsurface Purplish,lodgedplantscutbelowground Wilting,ordeadheart,oftenduetotunnelingoflargerplantsbyolder

instars CutcornleavespartiallyburiedinburrowsTheremovaloftheblackcutwormsweedhostsatornearplantingoften

setsthestageforinjurytoseedlingcorn.Theinjuriouscuttingstage(fourthinstartopupation)lasts212 to3weeks(dependingontemperature).Cornis


17/52


18/52


SYMPTOMSUnnatural growth

Stem tw isting or excessive tillering may be due to growing pointinjury by insects that bore into corn.

Tunneled plants that survive may also express Dead heart (center leaves wilt and die) Stunt ing and delayed development Barrenness or small ears

Although incidental to the more serious growing point injury,holes produced in the leaves by tunneling or drilling activity can bediagnostic.

Stem twi stin g. In jur y to the grow- Stalk borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 18 i ng poin t by stal k borer can cause Irregular rows of large and ragged holes in emerging

twi sti ng of the stem. leaves are often the result of entry into the stalk . Examinewhorls for frass (excrement).

Billbugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Rows of small circular and symmetrical holes may be the

result of a billbug using its snout to gouge a cavity in thestem just below the soil surface. No frass is left in whor l.

Stink bugs Transverse row of oval holes usually ringed with yellow. No obvious puncture near the base of the plant, but may

have a slimy, decaying area inside the lower stalk where

the piercing-sucking beak has penetrated the stalk. An infrequent pest.

ArmonKeaster

MitchellRoof

photosbyLeeJenkins

Tr ansverse r ows of holes.Potenti al suspects ar e Stalk Borersmal l stalk borer s or bil lbugs.

Appearance / Life cycleThedistinctivelarvaearewhitewithbrownishpurplestripesextending

thelengthofthebody.Thereisapurpleheartorbandbehindthetruelegs,butthepurplishstripesandheartfadeinolderlarvae.Theadultmothslayeggsduringlatesummerongrassesandsomebroadleafweeds(e.g.,bromegrass,ragweed,smartweed,lambsquarters,andpigweed).ThelarvaetypicallyhatchinearlyMayandtunnelintoweedyhostplants. Larvaeeventuallyoutgrowtheiroriginalhostsandmigratetolargerdiameterplants,whichoftenincludecornifplantednearby.Larvaeactivelyfeedfor8to10weeks. Thereisasinglegenerationeachyear.

Diagnostic tipsThepresenceofnoticeablystuntedcornrowsnexttopermanently

Stalk bor er s. Young borers (left ) have a grassyareasorfencerowsmayindicateastalkborerinfestation.The

promi nent pur ple heart color ation that stalkboreristheonlylarvafoundinMissouriandIllinoiscornfieldsthat

fades as the lar va ages (r i ght) . hasadistinctdiagonalblackstripeoneachsideoftheorangehead.


19/52


Damage

Thestalkborermayattackcornatanytimeafteremergence,butthecornplantstolerancetoinjuryincreasesgreatlyaftertheV6growthstage.

Stalkborerscaninjurecornplantsintwoways: Leaffeedingisthemorecommonlyseentypeofdamage.Larvae

enterthewhorlfromaboveandfeeddeepinthewhorlleaves.Thisfeedingproducesirregularrowsofraggedholes,whichenlargeastheleavesunfold. Althoughfoliarfeedingmayappearsevere,itdoesnotreduceyield.

Drillingintothebaseofthestalkisthemuchmoreseveretypeofinjury.Destructionofthegrowingpointduringboringtypicallyresultsindeadheartoftheinnerwhorl,althoughtheouterwhorlleavesremainhealthy.Tunneledplantsthatsurviveareoftenstuntedanddelayedindevelopment,showunnaturalgrowthsuchasstemtwistingandexcessivetillering,andcaneitherbebarrenorproducesmallerears.

ManagementAswithotherstalk-boringinsectpests,insecticidetreatmentisnoteffective

oncestalkborershavetunneledintocorn.Therefore,controlmeasuresshouldbeproperlytimedtotargetvulnerablestages,suchaseggs,newlyhatchedlarvae,andmigratinglarvae.Managementoptionsincludethefollowing:

Plantearlyinfieldswithahistoryofstalkborerdamage,orifthereishighpotentialforinfestationduetograssyweedproblems.

ControlgrassyweedsinthefieldbeforeegglayingbeginsinAugusttominimizeproblemsthefollowingseason.

Burngrasswaterwaysandditchesbeforespringgreen-upinfieldswithoutgrassyweedproblems. Ifgrassyareasarenotburned,scoutthefirsttwocornrowsfor

migratinglarvaeandleaffeeding,ortargethatchinglarvaebysprayingegg-layingsiteswithapyrethroidinsecticide.However,timingthisactivityisdifficult.

Beginscoutingborderrowswhen1,300to1,400degree-days(base41degreesF)haveaccumulatedsinceJanuary1,todetermineiflarvaearemigratingintocorn.

Recurrent,fieldwideinfestationscanbetreatedafterhatchbyaspringapplicationofaburndownherbicide(toforcelarvaeoutofgrassyweedhosts)incombinationwithacompatibleinsecticide.

Economic injury levelTheeconomicinjurylevelisthelowestpestdensitythatcancauseeconomicdamage. Economicinjurylevelsforstalkborerriseascorngrows,doublingfrom14%ofcorninfestedattheV5stageto28%infestedattheV6stage. Aninsecticidetreatmentofborderrowsmaybejustifiedifonly10%ofV2cornisinfestedwithstalkborer.(Theseeconomicinjurylevelsassumeamarketvalueof$2.50/bushelcorn,managementcostsof$13.00/acre,and80%controlwithaninsecticide.)Targetlarvaewithaninsecticidebefore theyhavetunneledintocornplants(i.e.,whenstillfeedinginthewhorls).

Un

ivers

ityo

fIllino

is

Classi c stal k borer feedin g i nj ur y on leavesRagged holes ar e obvi ous in the shadow ofthe plant in thi s photo.

Stalk borer tun neli ng in jur y to growingpoin t. Survi vin g plants may express stun t

i ng, dead hear t, and stem twi sti ng.


20/52


Feedin g damage by thr i ps. Shin yblack f r ass pel lets are present wi ththr i ps damage.

BrianChristine


Nar r ow t r acks f r om flea beetl e feedin g.

Claybacked Cutw orm

Overall grayish body with broad

yellowish brown stripe down theback.

Small larvae pull leaves into burrows and feed from tip to base.

Larger larvae cut seedlings at orjust above the base of the plan t.

Like the dingy cutworm(page 16),overwinters as partially grownlarva and resumes feeding in earlyspring.

Economic thresholds are the sameas for black cutworm(page 17).

Fields most likely to sustain injury

Late-plantedcornfieldsaremostatriskaslarvaemigratefromtheirearlierweedorgrasshosts,becausecornyoungerthantheV7stageismorevulnerabletoinjury.

Damage(especiallyintilledcorn)isoftenconfinedtothefourborderrowsnexttoprimeegg-layingsites,suchasgrasswaterways,fencelines,andditches.

Inno-tillcorn,fieldwideinfestationsarepossibleifweedygrasscontrolwaspoorthepreviousseason.

IncidenceMayandJune

SYMPTOMS

Speckled or sandblasted leavesSpeckled or mottled leaves, especially on seedlings, may signal

the presence of thrips. Although this feeding injury may be confused with sandblasting from blowing soil, the shiny black frass(excrement) pellets do not appear on wind-damaged foliage.

Thrips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 21

Removal of plant tissueIrregular narrow lines or t racks scratched from top layer of

tissue

Leaf tissue is stripped from the top layer, and damage appears asirregular, narrow lines running parallel to the veins.

Corn flea beetle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Whole plants cut of f near base

Black cutworm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Most cutting is done by the black cutworm. It may be con

fused at times with its less common subterranean cousin,the claybacked cutworm, because of the similar appearance and feeding habits of the two cutworm species.

Sod webworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 An occasional pest in corn fol lowing sod or grassy fields.

(More tissue removal symptoms onpage 23)


21/52


22/52


LeeJenkins

MitchellRoof

Sod webworm . T he shi ny, dark spots onsod webworm s help to distin gui sh themfr om other lar vae in festi ng cor nfields inM ay.

Signs of sod webworm . L eaffeedin g or plant cutt in g canlook sim il ar t o black cutwormdamage. H owever, onl y sodwebworm s make sil k tunn elsat t he base of plants.

Sod Webworm

Appearance / Life cycleThelarvahasadarkbrownheadwithalightgray-brownbody.Ithas

numerous,polishedtubercles(darkspots)andissparselycoveredwithcoarsebristles. Theadults(moths)layeggsingrassyareas,andsmalllarvaeoverwinteruntilactivefeedingresumesinearlyMay.

DamageDamagecanappearsimilartoblackcutwormclippingwhenplantsare

cutoffatorjustbelowthesoilsurface,orsimilartocutwormorarmywormfeedingwhenholesarechewedinleavesoralongmargins.Becausesodwebwormsoverwinter,theymaybefoundslightlyearlierintheseasonthanblackcutwormlarvae.Cornplantsseveredearlyinthespringfrequentlyregrowbecausethegrowingpointisstillprotectedbelowgroundwhencuttingoccurs.

Diagnostic tipSodwebwormscanoftenbefoundinshort,silk-linedtunnelsatthe

baseofcornplants.Cutwormsandarmywormsdonotshelterinsilkentunnels(althoughsomecutwormsdoburrowinthesoil).

Confusing look-alikesDonotconfusesodwebwormswithEuropeancornborerlarvae,

whicharelessstronglyspottedandwithoutcoarsehairs.Inaddition,Europeancornborerlarvaedonotconstructsilkentunnelsorshelteratthebaseofyoungcornplantsandarenotencounteredsoearlyinthe

spring(May).

ManagementAlthougheconomicthresholdshavenotbeendevelopedspecificallyfor

sodwebworms,thresholdsestablishedforblackcutwormscanbeusedthroughtheV4growthstage.Economicdamagetocornbysodwebwormsisuncommon.

Fields most likely to sustain injurySodwebwormfeedingtendstobemoreextensivewhencornfollowssod

orverygrassyfields.

Incidence

MaythroughearlyJune


23/52

EMERGENCE TO KNEE-HIGH CORN (VE TO V8) 23

(Tissue removal symptomscontinued from page 20)

SYMPTOMS

Chunks of leaf tissue or enti re leaves eaten

Several insects will chew no tches along the leaf margins, severleaves from the plant, or feed so deep in the whorl that leaves Cut cor n plan t dr agged in to blackemerge ragged and torn. cutworm burr ow.

These leaf feeders generally damage corn from May through mid-June and are less active or hidden during the day. If you cannotfind the insect that you suspect caused the damage, look for associated plant injury or insect clues. Such evidence, in conjunction w iththe time of the season or stage of corn growth, may help pinpointthe culprit. Keep in mind that a single field may contain severalspecies of insect pests (e.g., cutworms, sod webworms, and billbugs).

Cutworms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pages 15, 16, 20 Although the dingy cutworm is the most common foliage

feeder in the cutworm complex in corn, the subterraneancutworms (black and claybacked) sometimes consumeclipped leaves or seedlings that are dragged into their bur- Sod webworm damage

to corn seedli ng.rows. Sod webworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Often hides in silken tunnels at the base of plants.

Leafrollers Web together the tips of corn leaves and feed inside. Not an economic problem.

Southern corn leaf beetle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Chews notches in the leaf margins and sometimes in the

stems.

(More symptoms of tissue removal onpage 24)

Leafr oller damage. Leafr oller s webtogether ti ps of l eaves for a pr otected feeding si te.

M

arl

inRice

Un

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fIllino

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Laura

Ka

bric

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24/52


(Tissue removal symptomscontinued from page 23)

SYMPTOMS

Look for different patterns of leaf feeding, the presence orabsence of stalk tunneling, and the location of larvae to distinguishstalk borer and armyworm damage.

Stalk borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 18 Leaf feeding deep in the whorl produces ragged holes as

emerging leaves expand.Rows of r agged holes. Reddish brown, moist frass (excrement) found in the whorl.

Leaf feedin g by stal k borer Tunneling through the stalk causes dead heart when thedeep in the whor l becomes growing po int is injured.obvious when the leaves expand.

Plants that survive growing point injury may be twistedand stunted, or tiller excessively.

Larvae frequently found inside stalks. Armyworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Margins of the leaves are stripped, sometimes to the mid-vein; corn up to V8 may be completely defoliated.

Feeding starts on the lower leaves and progresses up theplant.

No tunneling through the cornstalk or associated injurysymptoms (twisting, ti llering, etc.).

L ight l eaf feeding by arm yworm. Larvae hide under soil clods or crop residue during theI r regular notchin g of leaf mar gin s is usu- day.al ly t he fir st sign of their presence.

Small, sym metrical, roun ded holes in leaves

A transverse row of symmetrical holes across the leaves as theyunfurl may be the result of tunneling or drilling into the base ofcorn younger than V5. Black cutworms and sod webworms occasionally leave such signs of damage, in conjunction with their moretypical leaf feeding and cutting; however, the prime suspect is bill-

Classic bil lbug damage bugs. Adult bi llbugs gouge through stems at the base of seedlings(r ight ). Feeding resul ts in with their snouts, producing a row of circular to elliptical ho lestr ansverse rows of holes. across leaves as they expand.Asymmetr ical, l acy holes

Billbugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25in l eaves (below) f romsouther n cor n r ootworm

Lacy, skeletonized leavesbeetle feeding.If the leaves have asymmetrical, lacy holes or lesions, look for the

Southern corn rootworm beetle . . . . . . . . . . . . . . . . . . . . . . . 38 The adults will occasionally strip tissue from between the

veins so that the leaf appears skeletonized, with lacyfoliage.

MaureenODay

MitchellRoof

LauraKabrick

LauraKabrick


25/52

EMERGENCE TO KNEE-HIGH CORN (VE TO V8) 25

Southern Corn Leaf Beetle

Appearance / Life cycleThesoutherncornleafbeetleisgenerallyaninfrequentpestofseedling

corn. Theadultis316 inchlongandgray-brownandsometimesbronze-tinted. Bitsofsoilsometimesclingtoitsthickcoveringofshort,stiffhairsandserveascamouflage.Theadultbeetlesoverwinterandthendepositclumpsofeggsnearthebaseofcornassoonasplantsareavailable.Theoverwinteringbeetlesfeedinearlyspringoncorn,aswellasweedssuchascocklebur,smartweed,andcrabgrass. Southern cor n leaf beetl e. I t

may be dif ficul t to find

Damage because of i ts soil camouflage.Thebeetleschewholesintheleaves,andnotchesintheleafmarginsand

occasionallyinthestems. BasalclippingofcornuptotheV2stagecanoccurbutisnotascommonasfoliardamage. Cornseedlingscansometimesbekilledwhenthebeetlesfeedinlargeclusters.

Diagnostic tipsSoutherncornleafbeetlesmayinfestcornfromMaythroughmid-

June. Thus,theirseasonalfeeding,evidencedbynotchingintheleafmargins,oftenoverlapswithsimilardamagecausedbythreelarvalpests:cutworms,sodwebworm,andarmyworm.Inaddition,allfoursuspectsprefertofeedatnight. Thesoutherncornleafbeetleoftendropstothegroundandhideswhendisturbed,soitisdifficulttofind.Therefore,bepreparedtospendtimesearchingundersoilclodsandcropresidueforthefoliagefeeder(s)responsibleforthedamage.

Feeding damage by

Management southern corn l eaf beeThereisnoeconomicthresholdestablishedandnoinsecticidelabeledfor tl e. D amage can be

controlofthisinfrequentpestofseedlingcorn. confused wi th t hat ofblack cutworm.

Fields most likely to sustain injuryNo-tillcornorcornfollowinggrassorsodappearstobemoresusceptible

tofeedingbythesoutherncornleafbeetle.

IncidenceMaythroughmid-June

BillbugsAppearance / Life cycle

Althoughseveralspeciesofbillbugsarefoundincorn,themaizebillbugisthemostcommon. Maizebillbugsaregray-brownsnoutweevilsabout25 inchlong. Theyoverwinteringrassesandsedges(especiallyyellownutsedge),fieldresidue,orsoil. Inthespring,billbugsfeed,mate,andlayupto200eggsovera2-monthperiod. Thetinygrubsdevelopinsidethestem.Adultsareoftencrypticanddifficulttofind,evenaroundinjuredplants,becausetheircolorblendsinwiththesoilandtheyaremostlyactiveatnight.Billbugsseldomfly,buttheywillcrawlupto14mileinsearchoffood.Thereisasinglegenerationeachyear. Adult bill bugs.Le

eJen

kins

Un

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M

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inRice


26/52


Tr ansverse r ows of holes fr omadult bil lbug damage. Al thoughbil lbugs are dif ficul t to find i nthe field, l eaf damage may in dicate their pr esence.


WayneBailey

Young, pale green armyworm lar vae.L ar va on the upper r ight has the looper-li ke postu r e typi cal of young lar vae. Aslar vae age, they acqui r e char acteri sti c

str i pes.

Damage

Soonaftertheyemergeasadults,billbugsbeginfeedingoncornbyinsertingtheirlongsnoutsintothebaseofcornstalks.Anarrowfeedingslit(usuallybelowground)upto12 inchlonginthesideoftheyoungstalkisanindicationofbillbuginjury.Smallplantsmaybestuntedorevenkilledbybillbuggougingandfeedingonthetenderinnerstemtissues. Asleavesemergefromlargerinjuredplants,asymmetricalrowofholesappearsacrosstheleavesfrombillbugfeedingwhiletheleaveswerestillrolled.Iffeedinghasinjuredthegrowingpoint,excessivesuckeringanddistortedgrowthresults. Developinggrubsthatfeedinsidethestemsnearthesoilsurfacemayalsocausestunting.

ManagementLeaffeedingdoesnotresultineconomicinjurytothecrop.Controlis

warrantedonlyifasignificantnumberofplantsarebeinginjuredbygougingoftheinnerstemandadultsarestillpresent.Treatmentsarenoteffectiveagainstgrubsfeedinginsidethestem.Therearenoeconomicthresholdsestablishedforbillbuginjury.

Fields most likely to sustain injuryDamageismorecommonincornfollowingsodorinfieldsinfestedwith

yellownutsedge.

IncidenceAprilandMay

ArmywormThe armyworm is also referred to as the true armyworm to distinguish it from

other armyworm species (fall, yellowstriped, etc.). In outbreak years, large numbersof armyworms migrate from field to field, consuming grasses and grain crops.

Appearance / Life cycleThesand-coloredmothshaveasmallbutprominentwhitespotinthe

centerofeachforewing.Newlyhatchedlarvaearepalegreenandmovelikeloopers. Thefull-grownlarvaeare112 incheslong,nearlyhairless,anddull-greentobrownwithalternatinglightanddarkstripesrunningthelengthof

thebackandsides.InMissouriandsouthernIllinois,theoverwinteringarmywormpopulationofpartlygrownlarvaeissupplementedbyspringmigrants,whichtypicallyarriveduringthefirstweekofApril.Themothslaytheeggsofthefirstgenerationinlush,grassyvegetationinAprilandMay.Larvaefeedatnight(andonovercastdays)for3to4weeksongrasscrops,especiallycorn,sorghum,andwheat.Duringtheday,armywormsremainhiddenundersoilclodsorcropresidue.TherearetypicallythreegenerationsinMissouriandIllinoiseachyear,butthelarvaeofthefirstgenerationdomostofthedamage(inMayandJune).


27/52


Diagnostic tips

Twocharacteristicmarkingsdistinguishmid-sizetolargearmywormsfromotherstripedleaf-feedinglarvae,suchasfallarmyworms:

Darkbandsatthetopofeachproleg White-borderedorangestripesrunninglaterallyalongthebody

DamageIncorn,armywormsgenerallyfeedonthewhorlleavesofyoungplants;

thedamagefrequentlyfirstappearsasirregularnotchingofthemargins.Heavyinfestationsofarmywormsmaycompletelydefoliatecornlessthan8inchestallandmaystripallleaftissuetothemidribinoldercorn.Heavydefoliationcanoccurvirtuallyovernightifhighnumbersoffullygrownlarvaemoveallatonceintoaseedlingcornfield.

Armywormsundergogreatfluctuationsinpopulationfromyeartoyear,

reachingdestructivepeaksatsporadicandunpredictableintervals.Outbreaksappeartobemorecommonaftercool,wetsprings,dueinparttothesuppressionofnormalactivityoftheparasitoidsandpredatorsthatholdpopulationsincheck.

ManagementArmywormsgenerallyfeedduringthenightandhidebyday,sooften

theyarenotdiscovereduntiltheyareatleasthalf-grown.Scoutearlyinthemorningorlaterintheevening,whenlarvaemaybemoreactive.Ifanearlyinfestationisdetectedinagrassyborderorripeningwheatadjacenttocorn,sprayafewswathstoformabarrierstripbetweentheinfestationandthecornfield.Goodgrasscontrolwithinandaroundfieldsoftenreducesthelikelihoodofanarmywormoutbreak.

Cornoftenrecoversfrommoderatefeedingunlessthegrowingpointisdamaged. Treatmentmaybejustifiedwhen25%ofcornplantsaredamagedandlarvaearestillpresent.Avoidrevengesprayingwhencropdamageisdiscoveredaftermajordefoliation,becausethewormsareoftenlargeanddifficulttokillbythistime. Armywormslargerthan114 inchesarepreparingtopupate.

Fields most likely to sustain injury early in the season include corn no-tilled into

Asmallgraincovercrop Pastureorsod AfieldwithheavygrassyweedpressureOutbreaksusuallyoriginateinfieldsofsmallgrainorgrasses,especially

wherethereisrankvegetativegrowth.Therefore,cornfieldsadjacenttomaturingsmallgrainsarevulnerabletoattacklaterintheseason.Larvaemayalsomoveinunison(armies)frompastures,fencerows,orothergrassyareasastheydepleteafoodsupply.

DistributionInthetypicaltilledfield,infestationsarefirstfoundinfieldmarginswhere

armywormshavemigratedinfromamaturinggrainfieldorgrassyborder.

IncidenceMaytolateJune

M

arl

inRic

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Lee

Jen

kins

Lee

Jen

kins

Older arm yworm larva. L ook for darkbands at t he top of each pr oleg and thewhi te-bordered or ange str i pes along t heside.

Ar myworm defoli ation. Except for themi dvein , arm yworms may eat the ent ir eleaf. A par asi toids egg can be seen behindthe head r egion.

H eavy armyworm damage.L ar vae feed noctur nall y andtypically h ide duri ng t he day.


28/52

(V8 to VT)28

Knee-high to tasseling corn

OVERVIEW

From knee-high to tasseling stage, look for :

Leaf tissue removed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pages 28, 29

margin feeding or ragged holes in leaves small, circular holes or elongated lesions

Stalks malfor med. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

lodging or gooseneck grow th

Holes bored in stalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

LeeJenkins

AnastasiaBecker

SYMPTOMS

Leaf t issue removedChunks of plant t issue removed from leaf margins, or ragged holes

in leaves

Stalk borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 18

Typical gr asshopper feeding pattern . Transverse rows of ragged holes.

Grasshopper s often consume fol i age fr om Armyworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

the leaf mar gin s in ward. Margin feeding; starts on lower leaves and works upward. Fall armyworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Ragged holes anywhere in whorl leaves. Lots of moist, reddish brown frass.

Grasshoppers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Feed from margin inward. Corn earworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

More commonly seen feeding in ear tips. Ragged holes in whorl leaves. Moist, tan frass.

(Symptom s of leaf feeding con tinued onpage 29)

Fall arm yworm feedin g damage. Copiousamounts of f r ass are left i n the whor l whenfeeding.


29/52


30/52


Fall ar myworm. D iagnosti c featur es are awhi te, in ver ted Y-shaped sutur e on headand four black spots that f orm a squar enear the hind end.

W in dowpane feedin g byyoung fall ar myworm s.


JimJarman

AnastasiaBe

cker

LeeJenkins

Unlikearmyworms,fallarmywormsaredaytimefeedersandareparticularly

activeintheearlymorningorlateafternoon.Largerlarvaetendtobecannibalistic;generallyonlyonesurvivesineachwhorl.Full-grownlarvaepupateinthesoil,andthemothsthatlaytheeggsofthesecondgenerationemergeafter10to14days.WhileMissouriusuallyhasthreecompletegenerations,Illinoishastwotothreeeachseason.

Diagnostic tipsThreecharacteristicmarkingsdistinguishfallarmywormsfromother

stripedlarvaefeedingoncorn(especiallyarmyworms): White,invertedY-shapedheadsuture(seam) Fourdistinctblackspots(tubercles)inasquareontopofthe8th

abdominalsegment(nearthehindend) Nodarkbandsonthetopsoftheprolegs(asinarmyworm)

DamageDamagegenerallyhasnoeconomicsignificanceunlessfeedingisdeepin

whorlandinjurestheundevelopedtassel.Themostcommoninjuryistolate-planted,pre-tasselcorn,andthefeedingisoftenfirstnoticeableinearlytomid-July.Thefirstthreelarvalinstarsaresmallandleavewindowpanesinthefoliageastheyconsumethetoplayerwhileleavingthelowerleafsurfaceintact. Mid-sizedtolargelarvaecutlarge,ragged-edgedholesintheleavesofwhorl-stageplants,leavinglotsofmoist,reddishbrownfrassintheirwake. Asthelarvaefeeddeepinsidethewhorlondevelopingleaves,theyoccasionallykillthetasselbeforeitemerges.Latergenerationsoflarvaemaychewcircularpatchesofkernelsfromanywhereontheear.

Thefallarmywormmayboreanentryholethroughthehuskontheside

oftheeartofeedonkernels.Incontrast,cornearwormsenterearsthroughthesilkchannelandthereforedonotleaveentryholes.Also,cornearwormfeedingisoftenlimitedtotheeartips,butfallarmywormsdevourkernelsfromanypartoftheear.

ManagementAninsecticideapplicationmaybeeconomicallyjustifiedwhen75%of

plantsshowleaffeedingandlarvaearelessthan114 incheslong. Treatmenttocontrollarvaealreadyinsidetheearsisnoteffective.

Fields most likely to sustain injuryLate-plantedcorn,especiallyiflessthan3feetinheight,ismoresuscep

tibletowhorlandtasselinjury.Egg-layingmothsarealsoattractedtocorn

fieldswithanabundanceofgrassyweeds.

DistributionWhorl feeding by fall arm y- Larvaehatchfromlayeredmassesof50toseveralhundredeggsandthenworm. Ragged leaves ar e fir st movetoadjacentplants. Consequently,thereareoftenlocalizedhotspotsnoti ced aft er they have throughoutafield.expanded.

IncidenceJulythroughAugust


31/52

31KNEE-HIGH TO TASSELING CORN (V8 TO VT)

Grasshoppers

Appearance / Life cycleThetwomostcommongrasshoppersinMissouriandIllinoiscornfields

arethedifferentialandredleggedgrasshoppers.Thedifferentialgrasshopperisarobust,olive-greentobrownishgrasshopper,reaching134 inchesinlength. Theundersideofthebodyisyellow,withcomplete,blackchevrons(V-shapedpatterns)onthefemurs(thighs)oftheyellowhindlegs.Theredleggedgrasshopperisbrownishredandsmaller,lessthan1inchlongwhenfull-grown;hindlegsareredwithblackspines.Bothspeciesofthesegrasshoppershaveasinglegenerationeachyear.

Adultandnymphalgrasshoppersaresimilarinappearance,exceptthatthenymphsaresmallerandlackwings.Oldernymphscanbedistinguished

fromnewlyhatchedgrasshoppersbythedevelopmentofwingpads,whichresemblestunted,nonfunctionalwingsandextendtothesecondabdominalsegment.

Bothdifferentialandredleggedgrasshoppersoverwinterineggpodslaidinuncultivatedground,suchasfieldmargins,roadsideditches,fencerows,waterways,pastures,andno-tillfields.AfteregghatchfromMaytoJune,nymphsfeedfor2to3weeksongrassesandweedsintheirhatchingbeds.Nymphsrequireapproximately40daystoreachthewingedadultstage.Bothadultsandnymphsaregeneralfeedersandreadilymigratetoadjacentcropswhenthevegetationinhatchingsitesisconsumed,mowed,orlimitedbydrought.

Damage

Grasshopperswillattackmostabovegroundpartsofthecornplant:leaves,tassels,greensilks,andears.Theyfeedfromthemarginsoftheleavesinward,andheavyinfestationsmayconsumeallleaftissueexceptthemidrib. Insevereinfestations,thecornstandisstrippedofleavesandonlybarestalksremain.Cropdamageisusuallyworseinyearswhendroughtreducesnaturalvegetationandgrasshoppersmigratetosucculentcornfields.

ManagementTargetthelessmobile,smallernymphswhiletheyarestillconfinedto

thehatchingbedsalongfieldmargins.Youngergrasshoppersaremoreeffectivelycontrolledwithinsecticides,andtreatmentoverasmallerareaisrequiredbeforetheoldergrasshoppersdispersethroughoutthefield.Awalkingsurveythroughthehatchingsitesallowsaroughassessmentof

grasshopperpressure.Countthenumberofgrasshopperspersquareyardingrassyandweedyareasborderingfields.Takeatleastfivesurveysininfestedareastoderiveanaveragenumberofgrasshopperspersquareyard, Le

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D i ff er ent i al grasshopper s.

Redlegged gr asshopper. Red hin d legs andsmal ler over all size distin guish thi sgrasshopper fr om the dif fer ent ial .

withsurveyedareasatleast50feetapart.Treatmentmaybejustifiedifthereisanaverageof15ormorenymphs

oradultspersquareyardinnoncropfieldmargins.Theeconomicthresholdwithinthecornfieldiseightormorenymphsoradultspersquareyard.Donotmowgrassesinfieldbordersuntilgrasshoppersarecontrolled.Beforespraying,checkforthenaturalsuppressionofgrasshopperpopulationsbydiseases. Thepresenceofdeadgrasshoppersperchedhead-upatthetopofplants,tightlygrippingthestems,isevidenceofafungal

Several gr asshopper s feedingon leaves. Unl ik e man yother i nsects, grasshoppersar e easil y seen.


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European corn borer life stages and activities, based on

AccumulatedFirst occurrence of

(base 50o stage (or event) occurrencea Activity

0 First spring moth Mating and egg layingFirst generation:

212 12.3 Pin hole leaf feeding318 Second instar 5.1 Shot hole leaf feeding

435 Third instar 5.4 Midrib and stalk boringb

567 Fourth instar 5.5 Stalk boring792 Fifth instar 9.1 Stalk boring

1,002 Pupa 8.0 Changing to adult1,192 Adult moths 6.6 Mating and egg laying

Second generation:

1,404 c 7.4 Pollen and leaf axilfeeding

1,510 Second instar 3.8 Leaf axil feeding1,627 Third instar 4.2

midrib boring

1,759 Fourth instar 4.9 Stalk boringb

1,984 Fifth instar 8.5 Stalk boring

European Corn Borer: Ecology and Management. NorthCentral Regional Extension Publication No. 327, by Charles E. Mason et al.,1996.

a

stage since initiation of the previous stage listed, based on 30-year averagetemperatures recorded in Columbia, Missouri.

b

mature plants.c Peak egg hatch occurs 10 days or approximately 200 to 250 degree-days

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Table 1.

degree-days accumulated after appearance of first spring moths.

degree-days Days to first

F)

Egg hatch (first instar)

Egg hatch (first instar)

Sheath, collar, and

Published by Iowa State University, Ames, Iowa.

Average number of days required to reach the first occurrence of the

First-generation larvae bore into stalks earlier than second-generation larvae because the younger stalks are more tender than those of older, more

later than first hatch.

tiallyfeedonthesurfaceoftheleavesbeforemigratingdeepinsidethe

whorl. Firstandsecondinstarsremovemesophyllfromtheleavessothatalayeroftransparentepidermisremains,thuscreatingawindowpaneeffect.Whenthesetender,newlydevelopingleavesgrowoutfromtheinfestedwhorl,theyshowsignsoffeedingrangingfrompinholestothedistinctivebuckshotappearance. Asthelarvaegrow,theycrawloutofthewhorlandbegintofeedonleafsheathsandtunnelintomidribs. Afterreachingthethirdinstar(approximately12 inchinlength),larvaeboreintothestalks,usuallyatoneofthelowernodes,andfeeduntilpupation. Frassandsilkatentranceholessignalthepresenceofborersinsidethestalks.First-generationlarvaepupateinearlyJulyandproduceadultsthatlaytheeggsofthesecondgenerationinmid-July.

W in dowpane feedin g byear ly i nstar s of Eur opeancorn bor er.

Buckshot damage byEur opean cor n bor er.

Spli t stalk s. Ent r y tun nel made by mi dsiz e Eur opean cor n borer i s vi sible (left).As lar va gr ows inside stal k, i t excavates alar ger tun nel (r ight ) whi ch weakens thestalk.


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Classic signs of second- generat ionEur opean corn borer feedin g. L ook forwindowpanes, r ounded holes, and f r assaround the leaf coll ar area.

Shot-hole feedin g damage and fr assmade by young Eur opean cor n borerlarva.

UniversityofNebraska

LeeJenkins

JimJarman

Fr ass at Eur opean corn bor er s ent r y holein to midr ib. By the time the borer populati on begins tunnelin g int o the mi dri b or thestal k, i t i s often too late to apply in secti ci de.

Second generation: Second-generationborerstypicallyinfesttasseling

andsilkingcorn.Eggmassesaverage20to30eggsforsecond(summer)flightmoths. About90%ofeggmassesaredepositedonthelowertwo-thirdsoftheundersidesofthethreeleavesaboveandbelowtheprimaryear,ontheearhusk,andontheundersideoftheear(i.e.,withintheearzone).Egglayingduringthesecond(summer)mothflightnormallyoccursovera3-to6-weekperiod,withpeakeggdeposition10daysafterthefirsteggsaredeposited.

Approximately75%ofthenewlyhatchedlarvaefeedonsheathandcollartissueandonpollenthathascollectedinleafaxils;theremaining25%movetotheear.Thirdinstarsfeedonsheathandcollartissueandtunnelintomidribs. Thestalksofthemorematurecornaretoughertopenetratethanthetenderstalksinfestedbyfirst-generationborers.Bythefourthinstar,themajorityoflarvaetunnelintothestalkwithinandabovetheearzone;

somewillcontinuetofeedintheearorboreintothetasselorearshank.Duringthefifthinstar,larvaepreparetoenterdiapause,orpupateandbecomemoths. Diapause,inducedbydaylengthandtemperature,preparesthepopulationforsurvivalduringthewinter.

Third-generation larvae: Second-generation(thirdflight)mothslayeggstoproduceathirdgenerationinthesouthernportionsoftheCornBelt(e.g.,theMissouriBootheel)eachseason. Theseeggsareusuallydepositedontasseledcornplantswhenthekernelshavenotmaturedbeyondthemilkstage. FromSeptemberthroughfrost,thefull-grownlarvaeconstructflimsy,silkencocoons,typicallyinsidethecornstalk,butoccasionallyundertheleafsheaths. Thelarvaethenenterdiapauseandoverwinter.Thefirsthardfreezekillslarvaethathavenotreachedthefifthinstar.

DamageEuropeancornborerdamage(byfirst-andsecond-generationlarvae)is

primarilyphysiologicalbecausetunnelingthroughtheconductivetissueofthestalkdisruptsthecornplantsplumbing.Theplantsabilitytoproducemaximumyieldisreducedbytheinterruptedtransportofnutrientsandwater.Lossesaremostlyduetopooreardevelopment;however,brokenstalksandlodging,droppedears,andsecondaryinvasionofstalkrotsinsusceptiblevarietiesalsocontributetoreducedyield.

Signsoffirst-generation Europeancornborerinfestationbeginatthemid-whorlstage:

Pinholeorwindowpanefeedingonleaves Buckshotappearancewhenleavesgrowoutofinfestedwhorls

Brokenmidribsfromtunneling(latesecondandearlythirdinstars) Frassatentryholes:afterreachingthethirdinstar,larvaeboreinto

stalks StalksbrokenatoneofthelowernodesSignsofsecond-generation Europeancornborerinfestationbeginat

thetasselingstage: Eggmasseslaidontheundersidesofleavesintheearzone Frassorsmalllarvaeinthesheath,collartissue,andleafaxilsoftheear

zone Brokenmidribsfromtunneling(thirdinstars) Frassatentryholes:afterreachingthefourthinstar,larvaeboreinto


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stalks(typicallyintheearzone),tassels,andearshanks

Brokenstalks(inandabovetheearzone)andtassels Droppedearsfromshanktunneling Feedingorskimmingonkernels

ManagementInformationonscoutingproceduresandworksheetstoaidininsecticide

treatmentdecisionsareincludedintheAppendix(page48).AlsoconsidercontrollingEuropeancornborerbyplantingtransgenicBthybrids(withrefugesofnon-Btcorntomanageresistance).

Fields most likely to sustain injuryAlthoughcornissusceptibletoEuropeancornborerinfestationafterthe

V6growthstage,spring-flightmothsaremoreattractedtotaller,early-

plantedcorn.Larvalsurvivalishigheronoldercornplantsatthemid-tolatewhorlstage(V8toV12)becauseoflowerconcentrationsoftheplantcompoundDIMBOA,abuilt-ininsecticidethatinterfereswiththesuccessfuldevelopmentofEuropeancornborerlarvae.Summer-flightmothsprefertodeposittheireggsduringpollenshedinlate-plantedfieldswithfreshsilks.

Lowwindvelocityandhighhumidityarefavorableforegglayingbymothsandforeggsurvival,becausetheseconditionsreducelossesfromdesiccation. Thecombinedeffectsofhightemperature,lowhumidity,andhighwindsincreaseeggandlarvalmortality.Heavyrainmayinhibitbotheggdepositionandsurvivalofnewlyhatchedlarvae.Thesurvivalrateofearlyinstarlarvaeaveragesabout20%,dependingonenvironmentalconditions,thecornstageinfested,andhybridresistance(tofirst-generation

attack).

IncidenceJunethroughearlyJuly(first-generationlarvae)andmid-Julythrough

earlySeptember(second-generationlarvae)

Southwestern Corn BorerThe southwestern corn borer is primarily a pest of the southern Corn Belt and is

economically damaging in the Bootheel of Missouri and in the southern quarter of

Illinois.Appearance / Life cycle Southwestern corn bor er

Mothsaredullwhiteandhaveawingexpanseofapproximately114 moth.inches. Fresheggsarewhiteandgenerallylaidingroupsoftwotofive,overlappingslightlylikefishscales.Althoughmosteggsarelaidontheupperleafsurface,theymayalsobedepositedonthelowerleafsurfaceandoccasionallyonthestalk. Within36hours,eacheggdevelopsthreetransverseredbands;eggshatchin4to5days.TheredbarstagecanhelpdistinguishEuropeancornborereggmassesfromthoseofthesouthwesterncornborer.Thesummer-formlarvaisoff-white,witharegularpatternof Te

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Numer ous broken midr ibs. L eavesappear snapped near t he midpointas a consequence of mi dr ib tu nn eling by second-generati on Eur opeancorn bor er.

Red bands areun ique to southwestern cornborer eggs.


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Sout hwestern cor n bor er l ar vae. Summer f orm has blackspots (top); overwi nteri ng formis immacul ate, or spotl ess (bot

tom).

LeeJenkins

LeeJenkins

U

niversityofIllinois

W in dowpane feedin g by southwesterncorn bor er. D amage is more extensivethan the same type of whor l feedin g byEur opean cor n bor er.

blackspotsthatbecomeconspicuousbythethirdinstar.Thefull-grown

larvalosesitsspotsthroughamoltattheonsetofhibernation;thisuniformlypaleyellow,overwinteringlarvaisknownastheimmaculateform.Full-grownlarvaeare114 incheslong.

Thesouthwesterncornboreroverwintersasanimmaculatelarvainthelowerpartofthestalk,belowgroundlevel.AfterpupationinlateMay,themothslayeggsthatproducethefirstgenerationofborers.Larvaeinfestingyoungcornmovetotheinnerwhorl,wheretheirfeedingproducesextensiveshotholesandelongatedlesionsintheexpandingleaves. LiketheEuropeancornborer,thelasttwoinstarstunnelandfeedwithinthestalk.Full-grownlarvaepupateandemergeasmothstolaytheeggsofthesecondgenerationbeginninginJuly.

Althoughsouthwesterncornborereggsarelaidmostlyontheuppersurfacesofleavesovertheentireplant,theyareconcentratedneartheearon

themiddlesevenleavesofthetasseledplant. Smalllarvaefeedprimarilyonlowerearshoots(concealedbytheleafsheaths)andbetweenhusksofprimaryears.Half-grownlarvaetunnelwithinthelowerhalfofthestalk.

Full-grownlarvaetypicallytunneldownthestalktothebaseoftheplantjustbelowthesoillinebeginninginlateAugust. Theygirdletheinnerstalk2to4inchesabovethebaseoftheplantwhileconstructingahibernationcell.Thisgirdlingactivitycauseslodgingandstalkbreakage,resultingindirectearlosses. Cornisgenerallyharvestedbeforethegirdlingactivityofthethirdgenerationbegins.

DamageSouthwesterncornborerdamageisprimarilyduetotunnelingand

girdlingofthestalkbytherobustlarvae.Tunnelingthroughtheconductivetissueofthestalkinterfereswiththetransportofnutrientsandwater,thusimpairingtheplantsabilitytoproducemaximumyield.Yieldlossesareduetopooreardevelopmentandalsobrokenorlodgedstalksresultingfromthegirdlingactivityofborerspreparingforwinter.StalkgirdlingbeginsduringthelastweekinAugustandislargelycompletedbymid-September.Withtheexceptionofinnergirdlingofthelowerstalk,damageissimilartothatofEuropeancornborer(refertoDiagnostictips).

Signsoffirst-generation southwesterncornborerinfestationbeginningatthewhorlstage:

Elongatedstrippingorwindowpanefeedingofleaves Buckshotappearancewhenleavesgrowoutofinfestedwhorls Deadheart(deathofthegrowingpoint)

Frassatentryholesonthelowerpartofthestalk StalksbrokenatoneofthelowerinternodesSignsofsecond- and third-generation southwesterncornborerinfesta

tionbeginningatthetasselingstage: Eggmasseslocatedmostlyneartheearonthemiddlesevenleaves Frassorsmalllarvaeunderlowerleafsheathsandontheears Frassatentryholesinthelowerhalfofthestalk Stalkbreakagecausedbygirdlingoftheinnerstalk2to4inchesabove

thesoilline


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Lodged plant. Cor n maygr ow upwar d i n a gooseneckshape to compensate for lackof r oot support caused by cornrootworm pruni ng.

JimJarman

Marlin

Rice

Spli t the stal k t o ident i fy the pest.Eur opean corn bor er is inside tun nel i nstalk.

SYMPTOMS

Stalks malformedLodging or grow ing upw ard in a gooseneck shape

A likely cause of lodging or goosenecking in continuous corn isroot pruning by corn rootworm larvae. Shallow roo ting in wet orloose soil or misapplication of the grow th regulator herbicide 2,4-Dmay also result in the gooseneck grow th o f cornstalks in any rotation system, especially follow ing periods of high winds. Although

2,4-D injury sometimes results in malformation of the brace roots, itmay still be advisable to dig up root masses of goosenecked plantsto eliminate shallow rooting as a cause and confirm the presence of

Corn rootworm larvae . . . . . . . . . . . . . . . . . . . . . . . . . . page 38

Holes bored in stalkA coil of f rass may trail out from the entrance hole into the stalk.

The feeding cavity may be easily seen if the stalk is split, and oftenthe tunneling larva can be identified as

Stalk borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 European corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Southwestern corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Southern portions of Missouri and Illino is.

Corn RootwormsCorn rootworm larvae are the most serious insect pests of continuous corn in the

Midwest, including Illinois, but they are not a major economic threat in Missouribecause of the small amount of continuous corn acreage. There are three species ofcorn rootworms found in Missouri and Illinois. Although western and northerncorn rootworm larvae can both cause serious damage, the western corn rootworm isthe dominant species in both states.

Gr oup of cor n r ootworm l arv ae. Appearance / Life cycleCornrootwormlarvaearewhitewithbrownheadsandslenderbodies.

Full-grownlarvaeareabout12 inchlong,andthereisadarktailplateonthetopoftheterminalsegment.Thesoutherncornrootwormisnotconsideredaneconomicpestinmidwesterncornproduction.

Westernandnortherncornrootwormbeetlesare14 inchlong,andsouth


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Generally,economicyieldlossoccurswhenrootratings(seetheIowa

StateUniversityscale)exceed3.0to3.5;lodgingmayoccuratratingsof4.0ormore.ThefirstindicationofrootworminjurymaybeinlateJuneorearlyJulywhenplantsfalloverafterstrongwindsandheavyrainfall.Yieldlossesdependonthenumberoflarvaeperplantandonplantmaturity,soilfertility,andamountofmoisturefollowingpeakinjury,aswellastheabilityofthehybridtoregenerateroottissue.Droughtstressworsenstheeffectsofrootpruning.Conversely,infestedplantsmayseverelylodge

Unive

rsityofIllinois

(becausetheylackrootsupport)whenwindandrainstormsoccurnearthetimeofpeaklarvalinjury.

Cornrootworminjuryresultsinyieldlossesinthefollowingways: Rootpruningandtunnelingdisruptthetransportofnutrientsand

waterfromtherootsystem. Lackofrootsupportcausesgoosenecklodging,whichmaycomplicate

harvesting. Rootfeedingpromotesinvasionbysecondarypathogenssuchasbacte

riaandfungi,increasingtheincidenceofrootrots.

Row of goosenecked cor n. Adultfeedingrarelyhasanimpactonyieldandconsistsof Strippingoftheupperlayeroftissuefromtheleaves;morelikelyto

occuriftasselshavenotemergedandpollenisnotavailable Silkclipping

ManagementAnnualcroprotationisthemostreliableandeconomicalmeansofman

agingrootwormpopulationsthroughoutmostoftheCornBelt.Certainpopulationsofnortherncornrootwormsinmorenorthernstatesmayundergoextendeddiapause,inwhichtheeggsremaindormantinthesoilfortwowintersbeforehatching.However,extendedeggdiapausedoesnotcurrentlyoccurinMissouri.Inaddition,westerncornrootworminjurytofirst-yearcornplantedaftersoybeanshasbeenreportedinareasofintensecorn/soybeanrotationineast-centralIllinois,northernIndiana,southernMichigan,andwesternOhio.Researchsuggeststhatageneticvariantofthewesterncornrootwormisselectingsoybeanfieldsasanotheregg-layingsite(inadditiontocorn).Despitetheseexceptions,croprotationstillprovidesthemostconsistentcontrolofrootworminfestations.

WesternandnortherncornrootwormadultscanbecountedincornfieldsinJulyandAugusttoassesstheneedforaninsecticideapplicationthenextspringinfieldswherecornwillbeplanted.Anaveragepopulationof0.75ormorebeetlesperplantinlatesummerislikelytolayenougheggsto

causeaneconomiclarvalinfestationthefollowingseasonincontinuouscorn.

InareasoftheCornBeltwherewesterncornrootwormadultslayeggsinsoybeanfields,scoutingforadultsinsoybeansispossiblebyusingsweepnets,visualobservations,oryellowstickycards.However,establishedthresholdshavenotbeenverifiedwithextensivefieldtesting,soscoutingforwesterncornrootwormsinsoybeansusuallyrevealsonlypresenceorabsenceofthebeetles. Decision-makingthresholdsareunderdevelopmentandcanbeobtainedfromextensionspecialistsintheaffectedstates(Illinois,Indiana,Michigan,Ohio).

InsomeareasofNebraska,thefocusofcornrootwormmanagementhas


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KNEE-HIGH TO TASSELING CORN (V8 TO VT) 41

beenthecontrolofadultstopreventegglaying.However,insecticidecon

trolfailuresforadultwesterncornrootwormshavebeenontherisesincethemid-1990s. Resistancetomethylparathionandcarbarylinthewesterncornrootwormbeetlepopulationhasoccurredwhereadulticideshavebeenappliedoverwideareasformanyyears.

Controlofadultsforsilkclippingisrarelynecessaryunlessgreensilksarebeingclippedbackto12 inchorlessbefore50%pollenshed.

Therearenoconsistentlyreliablescoutingmethodstomonitorcornrootwormlarvae.However,aninsecticidetreatmentduringcultivationmaybejustifiediftwoormorelarvaeperrootmassarecountedina7-inchcubeofsoilsampledfromuntreatedfieldsinearlyJune.Althoughsuchrescuetreatmentsaregenerallyequalto,ormoreeffectivethan,planting-timeinsecticideapplications,timingiscritical.

Fields most likely to sustain injuryCornplantedaftercornismostsusceptibletoinjurybycornrootworms,withtwoexceptions:

areasineast-centralIllinois,northernIndiana,southernMichigan,andwesternOhiowherewesterncornrootwormslayeggsinsoybeans

areaswhereextendeddiapauseinnortherncornrootwormsoccursInaddition,theperformanceofsoilinsecticidesisreducedwhencorn

plantinginearlytomid-Aprilisfollowedbycool,wetweatherthatdelaysrootwormegghatch.

Thechancesforadultsilkfeedingandegglayingareincreasedinlate-plantedcornbecausesuchfieldsarelikelytopollinatelaterandattractmoremigratingrootwormbeetles.

IncidenceEarlyJunethroughJuly(larvae)andlateJunethroughAugust(adults).


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(VT to R6)42

Tasseling to corn matur ity

OVERVIEW

At this growth stage look for :

Leaf ti ssue removed . . . . . . . . . . . . . . . . . . . . . . . . . . . . pages 42, 43

chunks of leaf tissue removed small circular holes or elongated lesions

Stalks malform ed or broken . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

lodging (goosenecking)

stalk breakage

Tassels damaged . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

tassel broken tassel eaten in whorl tassel discolored

Silks clipped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Ear damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

chunks of kernels removed tunneling or chewing damage ear drop

LeeJenkins

SYMPTOMS

Leaf t issue removedChunk s of plant tissue removed f rom leaf margins, or ragged holes

in leaves Armyworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 26 Late-season damage not common.

Gr asshopper damage. L arge, ir r egular Fall armyworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

chunks of l eaf t i ssue are removed to the Damage seen more frequently in late whorl stage corn.

midr ib as gr asshopper s feed. Grasshoppers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Serious only if large amounts of foliage are consumed

above the ear leaf.

(More leaf t issue removed symptoms onpage 43)


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TASSELING TO CORN MATURITY (VT TO R6) 43

(Leaf tissue removed symptoms continued from page 42)

SYMPTOMS

Small, circular holes or elongated lesions in leaves

European corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . page 32 Feeding of young, second-generation larvae may produce

holes (and occasionally lesions) in the collar area of leavesDamage to leaves in the

in the ear zone. ear zone by Eur opean Southwestern corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 corn borer.

Southern portions of Missouri and Illinois. Corn rootworm beetles (especially western) . . . . . . . . . . . . . 38

Beetles may occasionally strip the upper, green tissue fromleaves when pollen is unavailable.

Stalks malformed or brokenLodging or growing upw ard in a gooseneck shape

Corn rootworm larvae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Stalks brok en

European corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Goosenecking caused by Southwestern corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Stalks mainly broken at the base of the plant. cor n r ootworm feedin g.

Southern portions of Missouri and Illinois.

Tassels damagedTassels brok en

European corn borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Tassels eaten (in w horl )

Fall armyworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Stalk br eakage due to gir dli ng n ear

Tassels discolored gr ound by southwestern corn bor er.

Corn leaf aphid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

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Tassel eaten i nwhor l by fall ar myworm. Reddish pellets are fr ass.

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Corn l eaf aphi ds. Referto diagn osti c ti ps forhelp in disti ngui shi ngthem fr om other aphidsin cor n.

BrianChristine

LeeJenkins

Lar ge colony of corn leafaphids. Tan ones are aphidmummi es; whi te cast skin sar e also visibl e.

Corn Leaf Aphid

Appearance / Life cycleSmall,blue-green,soft-bodiedcornleafaphidsmaycolonizethetassels

andupperleavesofthecornplant.Theseglobularinsectsareabout116 inchlongwithblackantennae,legs,andtailpipes(cornicles).Femaleaphidsdonotlayeggsduringthegrowingseasonasotherinsectsdo,butgivebirthtoliveyoung. Therefore,populationscanquicklyreacheconomicallydamaginglevels. Individualsfoundinthespringarewinglessfemales.However,aspopulationsincreaseduringthegrowingseason,wingedfemalesareproduced;thesemobilefemalesdispersetolesscrowdedsitesandbeginnewcolonies. Exceptfortheirsmallersize,thenymphsaresimilartothewinglessadults.

Aphidsmigratefromthesouthandproduceasmanyas10generationseachyearinMissouriandIllinois. Cornleafaphidssuckplantnutrientsfromthephloemtissue,andexcessfluidconsumedbytheaphidsisexcretedasasugary,stickysubstancecalledhoneydew.Cornleafaphidpopulationsmayreachapeakinthewhorljustbeforethetasselingstageandlaterinfestthetassel,upperleaves,andear.

Diagnostic tipsCornleafaphidssometimescoexistonthesameplantasgreenbugs.

Greenbugsarelight,dusty-greenaphidswithadarkergreenstripeontheback,andonlythetipsofthecorniclesandlegsareblack.Birdcherry-oataphids,occasionallyfoundincornfields,areadarkerolive-greenwitharusty-redareabetweenthecornicles.

DamageHeavyinfestationsofcornleafaphidscauseyellowmottling,wilting,and

curlingofleaves.Themostseriousinjurytocornoccursbeforepollinationiscomplete. Incompletekernelformation,smallerears,andsometimesevenbarrenplantsmayresultfromheavywhorlfeeding2to3weeksbeforetasselemergence.Later,cornleafaphidsmayswarmoverthetasselandupperleaves,coatingthesurfacewithhoneydewandnumerouswhitecastskinsshedfrommolting.Inrarecases,tasselsandsometimessilksbecomesoheavilycoatedwithhoneydewthatpollinationisdisrupted.Honeydewmayeventuallyturndark,asthehighsugarcontentcreatesafavorablesubstrateforsootymolds. Injurysymptomsaremorepronouncedwhencornismoisture-stressed.Thecornleafaphidcantransmitbarleyyellowdwarf

virusandisalsoasuspectedcarrierofmaizedwarfmosaicvirus(expressedasmarginalcornleafnecrosis).

ManagementAninsecticideapplicationmaybejustifiedif thefollowingconditions

aremet: Atleast50%ofthetasselsarecoatedwithmorethan50aphids Infestationoccursduringpollenshedbeforepollinationishalfcom

pleted CornisunderdroughtstressMoisture-stressedplantsmaystillsufferyieldlossafterpollinationifthe


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TASSELING TO CORN MATURITY (VT TO R6) 45

upperleavesandtasselsremainheavilyinfestedwithcornleafaphids.

Insecticidalcontrolmaybeunnecessary,however,iflightbrown,parasitizedaphidmummiesandnumerouspredators(ladybeetlesandlacewing)arepresent.

Fields most likely to sustain injuryLate-plantedcornfieldsaremostsusceptibletocornleafaphiddamage.

IncidenceMid-Junethroughmid-August

SYMPTOMS

Silks clipped

OhioStateUn

ivers

ity

Several insects feed on green silks and clip them off before pollination is complete, causing some ears to fill only partially.However, control of insects for silk clipping is rarely necessaryunless green silks are continuously clipped back to 12 inch or less

before pollination is half complete. (Poll ination has occurred whensilks are turning brown and curling at the tips.) Grasshoppers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 31

Although grasshoppers readily consume foliage, they prefer to clip silks and chew on kernels during the early reproductive stages of corn. M issing ker nels due to in com

plete polli nat i on, caused by Corn rootworm beetles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

cli pped si lk s. Look for clipped green silks.

Corn earworm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Look for moist, light brown frass lodged in silks near the

ear tip. Japanese beetle

In eastern Illinois, large numbers of Japanese beetles (five

or more per plant) may clip enough silks to prevent properpollination.

Yellow woollybear Larvae clip silks, especially if flowering is delayed.

However, yellow woollybears tend to move readily fromplant to plant, reducing their impact on pollination.


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Corn earworm eggs on cornsilk.

Two color vari ations of corn earworm lar vae.

Cor n earworm lar va.F i ve oclock shadow i s vi sible above whit e band.Close- up (r i ght) r evealsblack mi cr ospines.

Cor n earwormdamage.General ly, feedin gi s concent r atednear the ear ti p.

LeeJenkins

LeeJenkins

ph

otosbyLauraKabrick

LeeJenkins

Corn EarwormAlthough the corn earworm (also known as cotton bollworm, sorghum head-

worm, and soybean podworm) infests more than 100 species of plants, corn is thepreferred host.

Appearance / Life cycleMothshavebuff-coloredwingswithirregularmarkingsandawingspan

of112 inches. Eggsareribbedandhemisphericalandapproximatelythesamecoloranddiameterasanindividualsilk. Larvaeareextremelyvariableincolor,rangingfromlightgreentopink,butalllarvaehaveatanheadandalternatingdarkandlightstripesonthebody.Thelarvaehavenumerousdarkspots(tubercles)withlongspines.Cornearwormcanbedistinguishedfromotherlarvaebytiny,thornlikeprojectionscalledmicrospinesthatgive

abristlyappearancewhenviewedunder10xmagnification.Larvaepassthroughfivegrowthstagesandare112 incheslongwhenfull-grown.CornearwormpopulationsintheMidwestmostlyarisefromspringmigra

tionfromsouthernstates,althoughpupaemaysuccessfullyoverwinterinsoutheasternMissouriandsouthernIllinois.Althoughmigratoryflightstrickleinasearlyasmid-AprilintheMissouriBootheel,thecornearwormarrivesinforcebymid-June. TherearetwoorthreegenerationsinMissouriandIllinois.

Thefirst-generationlarvaesometimesinfestthewhorlsifsilkingcornisunavailable. Mothsthatlaytheeggsofthesecondgenerationarehighlyattractedtofresh,greensilks.Eggsaredepositedindividually,andthenewlyhatched,pale-yellowlarvaetunnelthroughthesilkchanneltothedevelopingear.Larvaefeedforabout2to3weeks,consumingkernelsatthetipandalongthesideoftheear.Unlikethefallarmyworm,cornear

wormdoesnotboreanentranceholethroughthehusk,butdoessometimesleaveanemergenceholeasthefull-grownlarvapreparestopupateinthesoil. Third-generationlarvaemayattackverylat

corn - crop protection

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