managing insects and mite pests of texas...

B-12206-98

Managing

Insect and

Mite Pests

of Texas

Sorghum

CONTENTS

METHODS TO PREVENT INSECT PEST INFESTATIONS / 1Cultural management methods / 2Biological management methods / 3

METHODS TO DIAGNOSE INSECT PEST INFESTATIONS / 4Sampling / 4Economic threshold level / 5

CHEMICAL MANAGEMENT METHODS / 5Seed insecticide treatments / 5Soil insecticide treatments / 6Foliar and grain head-insecticide treatments / 6Endangered Species Act / 6Bees and other pollinators / 7Inbred lines for hybrid seed production / 7

SEED AND ROOT INSECT PESTS / 7Wireworms / 7Red imported fire ant / 8White grubs / 8Southern corn rootworm / 9

STEM AND LEAF INSECT PESTS / 10Cutworms / 10Yellow sugarcane aphid / 11Corn leaf aphid / 12Greenbug / 13Chinch bug / 14Corn earworm and fall armyworm (whorlworms) / 17Banks grass mite / 17

GRAIN HEAD INSECT PESTS / 18Sorghum midge / 18Corn earworm and fall armyworm (headworms) / 21Sorghum webworm / 22Grain head-feeding bugs / 23

STEM-BORING INSECT PESTS / 25Sugarcane borer, southwestern corn borer, neotropical borer and Mexican rice borer / 25Lesser cornstalk borer / 26Sugarcane rootstock weevil / 26

POLICY STATEMENT / 26

Managing Insect and Mite Pestsof Texas Sorghum

Greg Cronholm, Allen Knutson, Roy Parker, George Teetes and Bonnie Pendleton*

N INTEGRATED APPROACH TOmanaging insect and mite pestscan help Texas sorghum growersand crop protection specialists:

* Extension agent-pest management; Extension en-tomologists; professor of entomology; and researchassociate; The Texas A&M University System.

✦ Prevent damaging insect pest infesta-tions;

✦ Diagnose the presence and severity of aninsect pest infestation; and

✦ Control an infestation with insecticideswhen preventive methods are not fully ef-fective and sampling justifies the need forinsecticide.Sorghum has an advantage over other

grain crops because it can withstand rela-tively harsh, hot, dry climates, but respondswell to favorable production conditions andirrigation. The crop adds important agricul-tural diversity in a production region. Ben-eficial insects associated with sorghum of-ten help reduce the severity of insect andmites in sorghum and in other crops suchas cotton. Sorghum is an important rota-tion crop with cotton and soybeans, and ro-tation helps manage some weeds, diseasesand insect pests.

Some insect and mite pests can reachdamaging levels throughout the growingseason. Others can cause damage only at aspecific plant growth stage. Figure 1 illus-trates the probability of various insect andmite pests occurring at each plant develop-ment stage.

Most insect pests of sorghum are occa-sional pests, meaning they cause economicdamage in localized areas or only duringcertain years. Only one or two key insectpests are usually in any sorghum-growingarea in Texas. These insects occur most

AAyears and dominate control practices.Examples of key insect pests of sor-ghum are greenbug and sorghummidge.

Some pests, such as Banks grass mite,are induced. These are present in sorghumfields or surrounding areas, but usually innondamaging numbers. They increase toeconomically important levels after changesin cultural practices or crop varieties, or in-secticide use for other insect pests.

Methods to prevent insectpest infestations

Managing insect and mite pests of sor-ghum involves actions that prevent pestsfrom increasing to high enough numbers tocause economic damage. These practiceshelp avoid pests, reduce their abundance orslow their rate of increase, delay the timethey reach damaging levels and/or increasethe plant’s tolerance to the insect pest.

Figure 1. Sorghum insect pest occurrence.

Wireworm

White grubCutwormCorn rootworm

Yellow sugarcane aphid

Greenbug

Chinch bug

Corn leaf aphidCorn earwormFall armyworm

Spider mitesStalk borers

Corn earwormFall armywormSorghum webworm

Sorghum midge

False chinch bug Southern greenLeaffooted bug stink bugRice stink bug Conchuela stink bug

Grain maturityFlowering(Seedling) (Whorl) (Boot)

Vegetative growthStage of plant development

Seed

Cultural management methodsCultural management methods involve

using crop production practices to reducepest abundance or damage.

Crop rotation involves successive use ofhost and non-host crops. Sorghum benefitsmost when rotated with a broad-leaf or tap-rooted crop such as cotton or soybeans.Growing sorghum in a field planted to a dif-ferent crop the previous year significantlyreduces the potential for problems fromsome insect pests, diseases and weeds.

Crop rotation is especially effectiveagainst insect pests with a limited hostrange, long life cycle (one or fewer genera-tions a year) and limited ability to movefrom one field to another. For example, wire-worms, white grubs and some cutwormshave only one generation a year, must havea grass-type crop to develop and reproduce,and cannot move during the damaging lar-val stage from one field to another. Thus,growing a crop such as cotton or soybeansin the field before growing sorghum helpsreduce abundance of these soil-inhabitingpests. Sorghum growers should rotate cropsregularly.

Destroying the previous crop, volun-teer and alternate host plants eliminatesbreeding and/or overwintering habitats toreduce insect pest abundance and damage.This involves mechanically or chemically de-stroying sorghum plants soon after harvestto kill or expose insect pests and removetheir food supply. This method also includesdestroying volunteer crop and alternate hostplants within and outside a field.

Where conservation tillage practices areused, herbicides can be applied post-harvestto kill crop, volunteer and alternate hostplants. Herbicides stop crop growth effec-tively and are compatible with culturalmanagement practices to reduce insect pestabundance. Where crop residue must bedestroyed mechanically to expose overwin-tering insect pest life stages, conservationtillage may enable certain species of insectpests to become more abundant.

Destroying previous crop, volunteer andalternate host plants reduces insect pestabundance the following year. This practice

is particularly important to reduce theabundance of southern corn rootworm, cut-worms, sorghum webworm, sorghum midgeand stalk-boring insects. Johnsongrass is anon-cultivated host of many sorghum insectpests, including greenbug, yellow sugarcaneaphid and sorghum midge. Destroying thisweed is difficult but very helpful in manag-ing insect pests.

Seed selection, seedbed preparationand seed treatment are important in re-ducing the effects of sorghum insect pests.When deciding on a sorghum hybrid to plant,consider how well the hybrid is adapted tothe locale and its susceptibility to insectpests and diseases.

Use sorghum hybrids that tolerate green-bugs. Hybrids resistant to sorghum midgeare less available, but are highly advanta-geous in southern parts of the state. Sor-ghum hybrids with loose (open) ratherthan tight (compact) grain heads are lessinfested with larvae of corn earworm, fallarmyworm and sorghum webworm, all ofwhich feed on developing kernels. Also, sor-ghum with open grain heads is less likelyto show the effects of grain deteriorationfrom weather, grain head-infesting bugsand pathogens. Early, uniform hybridsavoid infestation by several insect pests,including sorghum midge, corn earwormand fall armyworm, in addition to avoidinglate-season weather problems.

Sorghum hybrids resistant to pathogensand with good standability also reduce thedetrimental effects of insect pests. Insectpests add to the stress on sorghum plantsduring the growing season, and, combinedwith pathogen infection, increase plant lodg-ing. Some insect pests, such as greenbugand corn leaf aphid, transmit maize dwarfmosaic virus and other sorghum diseases.This problem is best dealt with by using dis-ease-resistant sorghum.

Good seedbed preparation promotes rapidseed germination and seedling growth,which are essential to avoiding damage bywireworms, red imported fire ant and yel-low sugarcane aphid. Rapidly growing seed-lings are more tolerant of damage.

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Fungicide- and insecticide-treated seedprotects against some diseases and seed-feeding insects. Seed bought pre-treatedwith the systemic insecticide imidacloprid(Gaucho®) is protected against seed-feedinginsects and those such as aphids and chinchbug that attack sorghum during the seed-ling stage. However, this systemic insecti-cide also suppresses corn leaf aphids thatattract beneficial arthropods needed fornatural control of greenbug and other in-sect pests.

Planting time should be as early aspractical, but not when temperatures aretoo cool for rapid seed germination and seed-ling growth. In dryland areas of the state,early planting usually takes advantage ofseasonal rainfall patterns.

Early planting avoids infestation anddamage by some sorghum insect pests be-cause plants grow beyond a vulnerable stagebefore these insect pests are present. Also,young plants can reach a more tolerant stagebefore insect pests are present, be suscep-tible for a shorter period of time or maturebefore an insect pest becomes abundantenough to cause serious damage. Early-planted sorghum generally avoids damagingnumbers of sorghum midge, corn earworm,fall armyworm, sorghum webworm, stalkborers and grain head-infesting bugs.

Fertilizer and irrigation applied to sor-ghum can both help and harm effortsagainst insect pests. Using too much fertil-izer and irrigation can cause sorghumplants to be succulent and attractive to sor-ghum insect pests and extend the time tomaturity. On the other hand, healthy, vig-orously growing plants better tolerate in-sect pest infestation and other plantstresses. In areas with alkaline soils whereiron-deficiency is a problem, applying ironis important for production of healthy sor-ghum.

Chinch bugs and spider mites favor hot,dry conditions and stressed plants. Densestands of vigorously growing sorghum areless susceptible to chinch bugs. Rainfalltends to reduce greenbug and spider mitenumbers. Yield potential reductions by mostleaf-feeding insect pests partially depend onplant condition.

Biological management methodsBiological management methods reduce

insect pest abundance by using natural en-emies — predators, parasites and pathogensthat kill insect pests. Natural enemies canbe used in three ways:✦ Conservation, or enhancing numbers of

already existing natural enemies. Con-serving natural enemies is the most ap-plicable biological management methodto suppress the abundance of sorghum in-sect pests.

✦ Augmentation, the mass culturing andperiodic release of a natural enemy.

✦ Importation, the introduction of non-na-tive natural enemies.Conservation of natural enemies in-

volves protecting existing natural enemiesso they are abundant enough to suppress theinsect pests they attack. Sorghum hosts anabundance of natural enemies, primarily be-cause of aphid infestations. The corn leafaphid, usually non-injurious to sorghum, of-ten becomes very abundant. Corn leaf aphidsattract many different natural enemies thatattack aphid and caterpillar pests.

Natural enemies allowed to increase canhold some insect and mite pests below dam-aging levels. Insecticides often destroy natu-ral enemies, because most insecticides usedin sorghum are broad spectrum, killing in-sect pests as well as natural enemies. Thefact that insecticides kill natural enemiesis a primary reason for making sure insec-ticides are needed before applying them.Once natural enemies have been destroyed,there is no natural (biological) protectionagainst insect pests. This results in resur-gence of the treated insect pest or allows asecondary pest such as corn earworm orspider mites to increase.

Sorghum pests most affected by naturalenemies are greenbug, corn earworm, fallarmyworm, sorghum webworm and spidermites. Important natural enemies includeladybird beetles, lacewing fly larvae, syr-phid fly larvae, minute pirate bug, insidi-ous flower bug, damsel bug, big-eyed bugand parasitic wasps. Predators affect abun-dance and rate of increase of greenbugs, of-ten preventing them from causing damage.

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This is particularly true when greenbug-re-sistant hybrids are used. Parasites oftenterminate a greenbug infestation. Predatorsare important in suppressing abundance ofcorn earworms and fall armyworms thatinfest sorghum grain heads. Although sev-eral parasites attack sorghum midge, theireffect is minimal. Several pathogens, mostlyfungi, infect some aphids, chinch bug andcaterpillars.

Augmentation is the purchase and pe-riodic release of natural enemies not nor-mally occurring in sufficient numbers tocontrol pests. Commercially available natu-ral enemies sold for pest control in sorghuminclude convergent lady beetles, lacewingflies and the greenbug parasite Lysiphlebustestaceipes.

Naturally occurring convergent ladybeetles help control greenbug infestationsin sorghum. However, the convergent ladybeetles available to buy are collected fromnatural hibernating sites and stored in re-frigerators. When released in the field, theyquickly fly away or feed at low and ineffec-tive rates without reproducing.

The effectiveness of augmenting othernatural enemies for control of sorghum pestsis unknown. Because definitive informationon augmentation (when to apply, how manyto apply, etc.) is lacking, entomologists withthe Texas Agricultural Extension Servicecannot provide guidelines for augmentationas a management tool in sorghum.

Importation is the identification, collec-tion and release of natural enemies in areaswhere they do not occur naturally. Thismethod has been effective where an exoticpest has entered Texas without the naturalenemies that help control the pest in its na-tive country. Certain species of parasiticwasps and lady beetles that feed on thegreenbug have been imported and releasedin Texas.

Methods to diagnose insectpest infestations

SamplingSampling insects and mites in sorghum

is critical to determining the severity of aninfestation and need for insecticide appli-

cation. Insect pest numbers in sorghumfields can change rapidly. Inspect sorghumat least once a week, especially during criti-cal times when insect pests are likely to bepresent, to determine the pests present,their abundance and damage. Growers mayneed to inspect flowering sorghum dailywhen assessing abundance of sorghummidge. Record the information collectedduring each field inspection for future ref-erence to determine changes in insect abun-dance and plant damage.

The number of samples needed dependson the size of the sorghum field, uniformity,plant growth stage and severity of the in-sect infestation. Seldom are insect pestsdistributed evenly in a sorghum field. Ex-amine plants from all parts of a field. Avoidexamining only field borders. Take at leasttwo samples per acre in the sorghum field.

Growers can estimate the abundance ofmost insects in sorghum by visually inspect-ing the plants and plant parts. Some insects,especially those infesting sorghum grainheads, are effectively sampled by using the“beat-bucket” method. Insect pests that livein the soil are hard to detect and most needto be sampled before the crop is planted.

Soil-dwelling insects, such as white grubsand cutworms, can be found by searchingthrough the soil. Wireworms are difficultto detect in soil. A grain-baited trap can beused to attract them (See wireworm sec-tion on page 7 for details.)

For visual examination, randomly selectand carefully inspect plants to detect insectsand associated damage. During inspection,consider other factors such as predators,parasitized aphids, plant growth stage andcondition. Visual examination is used mostoften to sample aphids, chinch bug, spidermites and sorghum midge.

The beat-bucket technique is the bestway to estimate the number of corn ear-worm, fall armyworm, sorghum webwormand bugs in sorghum grain heads. Shakesorghum grain heads vigorously into a 5-gallon plastic bucket. Then count the cat-erpillars and bugs in the bucket. Becauseadult bugs can fly, take care to count thoseflying from the bucket or sampled plant.

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Economic threshold levelThe economic threshold level is the abun-

dance of an insect pest or amount of plantdamage that justifies applying insecticide.Although economic treatment levels pro-vided in this publication are based on re-search, consider them only guidelines, be-cause environmental and crop conditionsvary from year to year and region to region.

Economic treatment levels for most in-sect pests are provided in tables that con-sider differences in insecticide and appli-cation costs and per-acre value of the sor-ghum crop. To determine if the abundanceof insect pests justifies applying insecticide,first estimate the per-acre value of the crop.Then determine the per-acre cost of controlincluding the insecticide and application.Read across the columns for cost of controland down the table columns for the marketvalue of the crop. The abundance of the in-sect pest at that point in the table warrantsthe cost of control.

Chemical management methodsInsecticides are chemicals that kill in-

sects. They are powerful tools and have sev-eral advantages. The major advantage isthey are often the only practical control forinsect pests at or near damaging levels. Thekey disadvantages of insecticides are costand broad toxicity. They can harm nontar-get organisms in the crop and nearby ar-eas. From a sorghum insect managementstandpoint, cost of insecticide and killingnatural enemies are of most concern.

Use an insecticide in the proper amountand only when necessary to prevent eco-nomic loss. The cost of achieving full croppotential can exceed potential benefits. Ap-ply insecticides only when insect pests arebecoming more abundant and economiccrop loss is expected. When decidingwhether to apply an insecticide, considerthe cost of insecticide applications, prevail-ing market conditions, expected yield, in-sect pest abundance, insect age and dura-tion of attack, and stage and condition ofthe plants attacked.

Indiscriminate insecticide use can leadto pest resistance, resurgence of the treatedpest and outbreaks of secondary pests. Se-lective insecticide use by applicationmethod, choice of product or dosage cangreatly reduce occurrence of these prob-lems. Treating insect pests in sorghum canaffect the abundance of beneficial and pestinsects in adjacent crops.

Seed insecticide treatmentsGaucho®-treated seed can be purchased

to control wireworms, fire ant, greenbug,yellow sugarcane aphid and chinch bug. Useof Gaucho®-treated seed is discussed withinthe sections on these pests. Contact yourseed dealer to buy Gaucho®-treated seed.

Lindane can be used in the planter boxor as a direct seed treatment. To directlytreat seed, add 1 pint of water to each 100pounds of seed in a cement mixer or com-mercial or homemade seed treater and mixto fully coat the seed. Add insecticide slowlyand in the correct amount, thoroughly mix-ing until insecticide is distributed evenlyon all seeds. Treated seeds should beplanted within 20 days of treatment be-cause longer exposure to insecticide maylower seed germination of some sorghumhybrids.

Take care to avoid inhaling the dust whenplacing and mixing insecticide in a planterbox to treat planting seed. Use an old broomhandle, stick or similar device to mix in-secticide and seed in the planter box.

Lindane used on planting seed can delayand reduce seed germination when soil iscold and wet, or very hot. Lindane shouldat all times be used according to label in-structions. If the 7-day forecast is for a cold,wet period or the soil temperature is mar-ginal for seed germination, it may be bestnot to use lindane. Despite these precau-tions, lindane has been an effective, low-cost method of protecting sorghum plant-ing seed from insect attack. Do not usetreated sorghum seed for human con-sumption or livestock feed.

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Seed sometimes is treated with insecti-cides such as malathion, methoxychlor orpirimiphos-methyl to control stored-grainpests and do not control seed-feeding insectpests once seed is planted.

Soil insecticide treatmentsInsecticides for controlling some soil-in-

habiting insect pests must be applied be-fore the crop is planted or at planting time.Granular or liquid formulations may beused. The formulation used usually dependson available equipment and the target in-sect. Several application techniques areused to treat soil: preplant row treatment,row band at planting and in-furrow atplanting.

Preplant row treatment requires specialequipment to incorporate insecticide to adepth of 2 to 4 inches. Row treatments mustbe made after or during bed formation be-cause further cultivation or bed shapingchanges the position of insecticide in therow. For best control, treat a band of soil 7to 10 inches wide and 2 to 4 inches deep,and place seed in the center of the band.

Row band and in-furrow applicationsmay be used to apply insecticide to soil atplanting. The technique chosen depends onthe pest insect and how a particular insec-ticide is labeled. Mount the granular appli-cator spout or spray nozzle just behind theopening plow or disc opener and in front ofthe covering shovels or press wheel. Adjustspouts or nozzles to make the treatmentband 6 to 8 inches wide, treating the seedfurrow as well as covering soil. Incorporat-ing insecticide by covering shovels is ad-equate. Insecticide also can be incorporatedwith short parallel chains, loop chains,press wheels, finger tines or other suitabledevices. Do not apply insecticides directlyon seed unless the label clearly describesthat use, because doing so usually resultsin poor seed germination. In-furrow insec-ticide application for other insect pests doesnot adequately control white grubs whenthey are abundant.

Some insecticides (e.g., aldicarb, car-bofuran, disulfoton, phorate, terbufos) aresystemic and can be applied at planting.

Applied to soil, these chemicals are ab-sorbed into the young growing sorghumplant and control or suppress such early-season insect pests as greenbug, corn leafaphid, yellow sugarcane aphid and chinchbug.

Certain insecticides, besides being sys-temic, are effective against some soil-inhab-iting insect pests, such as wireworms andcorn rootworms. Duration of systemic ac-tivity varies with insecticide and rate, butgenerally suppress insect pests for 2 to 6weeks after application.

Foliar and grain-headinsecticide treatments

Aircraft or ground machines may be usedto apply insecticides to sorghum foliage andgrain heads. Aerial applications work bestwhen insecticide swaths meet or overlap.Insecticide sprays are more effective andhazards minimized when wind velocity isless than 10 miles per hour.

Nozzle size and number, ground speedand pressure influence the rate of insecti-cide spray output per acre by a ground ma-chine. Calibrate the sprayer carefully toensure the recommended amount of insec-ticide is applied. One nozzle per row usu-ally is adequate for young sorghum plantedin rows. Two to three nozzles may be neededto adequately cover larger plants and broad-cast-planted sorghum. Optimal pump pres-sure depends on the kind of nozzle used.

Some insecticides discolor foliage of cer-tain sorghum hybrids. Yield losses may oc-cur from extensive leaf damage after thesechemicals are used on susceptible hybrids.Review the label carefully before using aninsecticide. If you do not know whether thesorghum is susceptible to insecticide, con-sult the insecticide manufacturer and/orseed company. Carefully follow instructionson the label of an insecticide container toavoid hazards to the applicator, wildlife andthe environment.

Endangered Species ActThe Endangered Species Act is designed

to protect and recover animals and plants indanger of becoming extinct. Under

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provisions of this act, the U.S. Fish and Wild-life Service helps the Environmental Protec-tion Agency and Food and Drug Adminis-tration to implement pesticide programs byanalyzing the biological effects of pesticideson threatened and endangered species.

Many pesticide labels now list restric-tions limiting use of products or applicationmethods in areas designated as biologicallysensitive. These restrictions often change.Refer to Environmental Hazards of Endan-gered Species discussion sections of prod-uct labels and/or call your local county Ex-tension agent or fish and wildlife servicepersonnel to determine what restrictionsapply in your area. Regardless of the law,pesticide users can be good neighbors byknowing how their actions may affectpeople and the environment.

Bees and other pollinatorsProtect bees and other pollinators from

insecticides. Pollination by bees is impor-tant in producing such crops as alfalfa, clo-ver, vetch and cucurbits. Sorghum is animportant source of pollen for honey beesin many parts of Texas. However, sorghumis wind- or self-pollinated and does not re-quire insect pollinators.

Take care to minimize bee losses by:✦ Applying insecticides, if practical, before

bees move into fields or adjacent crops.When bees are present in the field or vi-cinity, make applications during theevening after bees have left the field.

✦ Where insecticides are needed, using ma-terials least toxic to bees and notifyingbeekeepers so they can protect bees.

✦ Preventing insecticide spray from drift-ing directly onto bee colonies.

Inbred lines forhybrid seed production

Inbred lines used for sorghum hybridseed production often are more susceptiblethan hybrids to insect pest damage and in-secticide phytotoxicity. The increased sus-ceptibility to insecticides and higher cropvalue of sorghum for hybrid seed produc-tion generally require lower economicthreshold levels for insect pests. Also, in-

sect pests that influence seed quality andgermination are more important in hybridseed production.

Monitor hybrid seed production fieldsregularly and consider the increased sus-ceptibility to insect pests and insecticidephytotoxicity. Before applying an insecti-cide, check the insecticide label carefullyand consult the manufacturer and seedcompany about possible phytotoxic effects.

Seed and root insect pests

WirewormsElateridae and Tenebrionidae

True and false wire-worms are immaturestages of click and dark-ling beetles. Wirewormsgenerally are shiny, slen-der, cylindrical and hard-bodied. Their color rangesfrom yellow to brown.

Wireworms feed on planted sorghumseed, preventing germination. To a lesserdegree, they feed on seedling plant roots,reducing plant stands and vigor.

Cultural practices that reduce abundanceof and damage by wireworms include:✦ Preparing good seedbeds and planting

when soil moisture and temperature areadequate to promote rapid seed germi-nation;

✦ Cultivating to reduce non-crop plantmaterial; and

✦ Planting sorghum in a field where a tap-rooted crop such as cotton was grown theprevious year.Sample fields before planting to deter-

mine the need to use insecticide-treatedseed or to apply insecticide at planting. Soilexamination and bait traps can be used tosample for the presence of wireworms.

To build a bait trap, place 6 to 12 ouncesof nontreated sorghum seed in a 4-inch wideby 6- to 8-inch deep hole in the soil. Coverthe hole with soil, and mark the trap witha stake. Covering the trap location with a4- by 4-foot sheet of black plastic warms thesoil and makes trapping more effective. At

Wireworm

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least 2 weeks before planting, install onetrap for each 10 to 20 acres. Two weeks later,examine the grain in the trap and count thewireworms. Also, growers may thoroughlyexamine soil samples 1 foot square by 4inches deep. If you find one wireworm larvaper square foot or two or more larvae perbait trap, treat either seed or soil with in-secticide.

Lindane applied as a seed or planter boxtreatment effectively controls wireworms.Information on seed treatment proceduresis contained in the section on seed treat-ment. Gaucho®-treated seed also is labeledfor wireworms. Applying some insecticidesin furrow at planting also may control wire-worms.

Red imported fire antSolenopsis invicta

Under certain condi-tions in the eastern andsouthern parts of thestate, red imported fireants feed on plantedseed. Worker ants chewthrough the thin seedcoat and remove the em-bryo (germ). They rarelyconsume the endosperm(starch) of the seed. Theyprefer water-soaked orgerminating seeds, butalso damage dry seeds.

Cultural managementpractices that reduce damage by wirewormsto planted sorghum seed also reduce red im-ported fire ant. Use seed with good vigorand plant into a well-prepared seedbedwhen soil temperature and moisture are

adequate for rapid seed germination.Firmly pack covering soil to prevent easyaccess of fire ants to planted seed and thusreduce damage by fire ants. Insecticide-treated seed as described for wireworms iseffective against red imported fire ants.Gaucho®-treated seed or in-furrow, at-plant-ing application of insecticide may provideeffective control.

White grubsPhyllophaga crinita and others

White grubs are thelarvae of May or Junebeetles. White grubs arecharacteristically “C-shaped” with white bod-ies and tan to brownheads and legs. Becausethe last abdominal seg-ment is transparent,dark-colored digestedmaterial can be seen inthe larva. Larvae vary insize according to age andspecies.

Rarely are white grubsserious pests of sorghum.However, because they can be present in afield at planting and cannot be controlled oncesorghum is planted, their presence must bedetermined before planting. Grubs damagesorghum by feeding on the roots. They maykill small seedlings, resulting in stand loss.Severely pruned roots of larger plants resultin plant stunting and lodging and increasedsusceptibility to drought and stalk rot organ-isms.

Planting sorghum in a field where a non-grass crop was grown the previous year isthe most important cultural managementtactic against white grubs.

To determine the abundance of white grubsbefore planting, examine 1 square foot of soilin each 5 to 10 acres. If more than two whitegrubs are found per square foot, severe dam-age to sorghum could result. No insecticidesfor white grubs are currently labeled forbroadcast, incorporated application. If whitegrubs average one per square foot, growers canadequately suppress them with an in-furrowor row band application of terbufos.

Red imported fire ant

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Table 1. Suggested insecticides for seed treatment forwireworms and red imported fire ants.

Lindane formulation % Lindane Concentrate

Gammasan® 16.6 3 oz./bu.

Seed Mate Lindane 25® 25 4 oz./cwt.

Sorghum Guard® 16.6 3 oz./bu.

RemarkSeed Mate Lindane 25®. If soil temperature is extremelyhigh (hot weather, mid-summer planting) reduce recom-mended dosage by one-half.

White grub

Southern corn rootwormDiabrotica undecimpunctata howardi

Southern corn root-worms are the larvae ofthe spotted cucumberbeetle. Rootworms aresmall, brown-headed andcreamy white, with wrin-

kled skin. They burrow into germinatingseeds, roots and crowns of sorghum plants.

Symptoms of rootworm damage includereduced stands and plant vigor, and occur-rence of “dead heart” in young plants. Laterin the season, maturity may be delayed,weeds may increase in abundance becauseof a nonuniform plant stand, and plants maylodge. Damage by southern corn rootwormsis most likely to occur in the area of Texasshaded on the map (Figure 2).

Granular or liquid formulations of sev-eral insecticides are labeled for in-furrowor row band application for controlling root-worm. Base the need for insecticide treat-ment on a field history of previous damageby rootworms. Rotating insecticides de-creases the possibility of rootworms devel-oping resistance. Seed treatment with lin-dane controls light infestations of root-worms present at planting.

Figure 2. Areas of potentially economically damagingsouthern corn rootworm infestations in Texas.

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Table 2. Suggested insecticide for controlling white grubs.

Days from lastInsecticide application to:

Toxicant per Concentrate/pound 1,000 ft. of row Harvest Grazing

Terbufos See remark (Counter® 15G) 8 oz. (Counter® 20CR®) 6 oz. 100 50

RemarkTerbufos. Apply once per season in a 5- to 7-inch banddirectly behind the planter shoe in front of the presswheel, and not in direct contact with seed.

Table 3. Suggested insecticides for controlling south-ern corn rootworm.

Insecticide Days from last(listed alphabetically) application to:

Toxicant per Concentrategallon or pound per unit area Harvest Grazing

Carbofuran See remarks (Furadan® 4F) 24-32 oz./acre 75 75

Chlorpyrifos See remarks (Lorsban® 15G) 4-8 oz./1,000

ft. of row

Terbufos See remarks (Counter® 15G) 4-8 oz./1,000

ft. of row (Counter® 20CR®) 3-6 oz./1,000

ft. of row 100 50

RemarksCarbofuran. Apply in seed furrow or 7-inch band andincorporate.

Chlorpyrifos. Apply once per season in a 6- to 7-inchband, behind the planter shoe and in front of the presswheel.

Terbufos. Apply once per season in a 5- to 7-inch banddirectly behind the planter shoe in front of the presswheel, and not in direct contact with seed.

NOTE: Lower rates of insecticides listed have been shownto provide most favorable economic returns; however,where high infestations consistently occur, use the higherinsecticide rate.

Southern corn rootworm

Stem and leaf insect pests

CutwormsAgrotis and Euxoa spp.

Cutworms of severalspecies can damage sor-ghum. Cutworms are im-mature stages of mothsthat are active at night.Cutworm moths prefer tolay eggs in grassy andweedy fields. Eggs arelaid on stems or leaves ofsorghum, grassy weeds

or in the soil, and hatch in 2 to 14 days.The typical cutworm larva attacking sor-

ghum is plump and curls into a “C” shapewhen disturbed. Larvae vary in color fromgrayish white to grayish black or browndepending on species. Fully grown larvaeare 1 to 2 inches long. Some species passthe winter in the soil as pupae and othersas adults; most overwinter as small larvaein cells in the soil, under trash, or in clumpsof grass. They start feeding in spring andcontinue growing until early summer, whenthey pupate in the soil. Larvae of most spe-cies remain underground during the dayand feed at night.

The most common cutworms in sorghum(surface-feeding cutworms) cut plants off at,slightly below or above the surface of thesoil. Some (climbing or army cutworms) feedon above-ground plant parts; others aresubterranean and feed on undergroundplant parts including roots of seedlings.

Cultural controls for cutworms includeplowing under or using herbicides to con-trol vegetation in late summer or early fall,destroying weeds and thoroughly preparingthe seedbed at least 3 to 6 weeks beforeplanting. Cutworms are more severe inweedy fields.

Determining the presence of cutworms insorghum is based on visible damage toplants. For surface-feeding and subterra-nean cutworms, determine the number ofsevered or dead and dying plants per foot ofrow. Base your decision to apply insecticideon the degree to which an adequate standis threatened. For cutworms that feed on

above-ground plant parts, significant lossesoccur when more than 30 percent of the leaftissue has been eaten.

Insecticide sprayed as a broadcast treat-ment on the ground and plants usually pro-tects against cutworms. However, cutwormsspend the day hidden in the soil. Late-af-ternoon applications sometimes are moreeffective. Insecticidal baits are available andeffective against some cutworms, but areexpensive. Insecticide applied at plantingcontrols subterranean cutworms. Apply theinsecticide in a 6- to 7-inch band and incor-porate it into the top 1 to 2 inches of soil.

Aerial or ground application of approvedinsecticide is effective in controlling cut-worms in an established sorghum stand.However, insecticide is more effective onclimbing than subterranean cutworms. Re-fer to Table 4 for insecticides suggested forcutworm control. Also refer to labels of in-secticides listed for southern corn rootwormcontrol for labeled use against cutworms.

10

Cutworm

Table 4. Suggested insecticides for controlling cutworms.



Chlorpyrifos See remarks (Lorsban®) (4E) 16-32 oz./acre 30-60 30-60 (15G) 8 oz./1,000

ft. of row

Cyfluthrin See remarks (Baythroid® 2E) 1.0-1.3 oz./acre 14

Cyhalothrin See remarks (Karate®1E) 1.92-2.56

oz./acre

RemarksChlorpyrifos. 4E - To minimize insecticidal injury, do notapply to drought-stressed plants or within 3 days afterirrigation or rain except where insecticide is applied inirrigation water. The waiting period from last applicationto harvest or grazing is 30 days for the 16-oz. rate and 60days for the 32-oz. rate.

Cyfluthrin. If applied once or twice, green forage maybe fed or grazed on the day of treatment. For three ap-plications, allow at least 14 days between last applica-tion and grazing.

Cyhalothrin. Do not graze livestock in treated area orharvest for fodder, silage or hay.

Yellow sugarcane aphidSipha f lava

Yellow sugarcaneaphids usually arelemon-yellow, but undersome conditions are palegreen, are covered withsmall spines and havetwo double rows of darkspots on the back. Bothwinged and winglessforms live in the colony.This aphid feeds on many

different grasses, including johnsongrassand dallisgrass. Females give birth for 28days to living young, averaging two nymphsa day by each female. Nymphs mature in13 to 19 days; adults live for 25 to 30 days.

Yellow sugarcane aphids feed on sorghumand inject toxin into leaves of seedlings andolder plants. Aphids feeding on seedlingplants turn the leaves purple and stuntgrowth. On more mature plants, leaves turnyellow. By the time discoloration symptomsare visible, plants have been injured signifi-cantly. Damage often leads to delayed ma-turity and plant lodging that may be wors-ened by associated stalk rots.

The presence of yellow sugarcane aphidsmust be determined soon after sorghumplants emerge. The presence of purple-col-ored seedling plants is an indication of ayellow sugarcane aphid infestation. Scoutsorghum by inspecting plants beginning thefirst week of plant emergence and twiceweekly until plants have at least five trueleaves. As plants grow larger, they becomemore tolerant of aphid feeding. Very smallseedling sorghum plants (one to three trueleaves) often are significantly damaged af-ter being infested for a week or less.

Discoloration symptoms may be useful inassessing yield losses, and may be used ina decision to replant. Information in Table5 describes plant damage and correspond-ing percentage yield loss associated withlevels of damage. Do not consider the firsttwo “seed leaves” when estimating damage.

Economic injury levels presented inTables 6 to 8 are based on percentage of yel-low sugarcane aphid-infested plants at the

Yellow sugarcane aphid

11

Table 8. Economic injury levels for yellow sugarcane aphidbased on percentage of seedling plants infested at thethree true-leaf stage.

Control Crop market value ($) per acrecost ($)per acre 100 125 150 175 200 225 250 275 300

Percent infested plants

6 67 53 44 38 33 30 27 25 24

8 89 71 60 51 44 38 36 33 32

10 * 90 76 64 55 48 44 41 39

12 * * 92 77 66 57 53 49 44

*Do not treat.

Table 7. Economic injury levels for yellow sugarcane aphidbased on percentage of seedling plants infested at thetwo true-leaf stage.



6 26 21 18 15 13 12 11 10 10

8 35 28 24 20 17 16 14 13 13

10 43 35 29 25 22 20 17 16 16

12 51 42 35 30 26 23 20 19 18

Table 6. Economic injury levels for yellow sugarcane aphidbased on percentage of seedling plants infested at theone true-leaf stage.



6 15 12 10 9 8 7 6 6 5

8 20 16 13 11 10 9 8 8 7

10 25 20 17 14 12 11 10 10 9

12 30 25 21 17 14 13 12 11 10

Table 5. Estimated yield loss based on damage by yellowsugarcane aphids to three true-leaf stage sorghum plants.

Description % Loss/plant

No discoloration 0

Localized discoloration 8

Less than one entire leaf discolored 11

One entire leaf discolored 31

More than one leaf discolored 54

More than two leaves discolored 77

Dying/dead plant 100

12

1, 2 or 3 true-leaf stage. Do not count thetwo seed leaves that appear first.

Many predators feed on yellow sugarcaneaphid, but the aphid is rarely parasitized.Insecticides are currently the only way tomanage yellow sugarcane aphids in sor-ghum. Gaucho®-treated seed or insecticideapplied at planting (carbofuran, disulfotonor phorate) reduces severity of yellow sug-arcane aphid infestations (Table 9).

Corn leaf aphidRhopalosiphum maidis

Corn leaf aphids ofteninfest the whorl and un-derside of leaves of sor-ghum in great numbers.This dark bluish-greenaphid is oval-shaped,with black legs, corniclesand antennae. There arewinged and winglessforms.

Corn leaf aphids are found most fre-quently deep in the whorl of the middle leafof pre-boot sorghum but also occur on theunderside of leaves, on stems or in grainheads. When feeding, corn leaf aphids suckplant juices but do not inject toxin as dogreenbug and yellow sugarcane aphid. Themost apparent feeding damage is yellowmottling of leaves that unfold from thewhorl.

This insect rarely causes economic lossto sorghum. In fact, they can be consideredhelpful. Beneficial insects such as ladybeetles are often attracted to feed on cornleaf aphids. When corn leaf aphid numbersrapidly decline at sorghum heading, thebeneficial insects are present to suppressgreenbug and other insect pests. These ben-eficial insects also are believed to move toadjacent crops, such as cotton, and helpmanage insect pests in those crops.

When abundant, corn leaf aphids are eas-ily seen within the whorl of sorghum plants.The whorl leaf can be pulled from the plantand unrolled to detect aphids when num-bers of aphids are low. Occasionally, cornleaf aphids will become so abundant on afew plants in a field that grain head exer-

Corn leaf aphid

Table 9. Insecticides for yellow sugarcane aphid.


Toxicant per Concentrategallon or pound per acre Harvest Grazing

Commercially treated seed

Imidacloprid Commercially (Gaucho®) applied 45

Applied at planting

Carbofuran See remarks (Furadan® 4F) 24-32 oz. 75 75

Disulfoton (Di-Syston®) (8E) 16 oz. (15G) 5.0-6.7 lb.

Phorate See remarks (20G) 4.9 lb.

Applied post-emergence

Carbofuran See remarks (Furadan® 4F) 8-16 oz. 75 75

Dimethoate See remarks (4E) 8-16 oz. 28 28 (5E) 6.4-12.8 oz. 28 28

Disulfoton See remarks (Di-Syston®) (8E) 4-8 oz. 07 45 (15G) 5.0-6.7 lb. 30 45

Parathion (ethyl) See remarks (4E) 16 oz. 12 12 (8E) 8 oz. 12 12

Phorate See remarks (20G) 4.9 lb. 28

RemarksCarbofuran. Applicator must use proper protectiveequipment when applying this highly toxic insecticide.Do not apply to foliage more than twice per season. Donot apply after heads emerge from the boot.

Dimethoate. Do not apply more than three times perseason. Do not apply after heads emerge from the boot.

Disulfoton. 8E - A maximum of three foliar applicationsmay be made, with the last application no later thanflowering. Post-harvest interval is 34 days for three foliarapplications. 15G - Granular formulation applied postemergence is recommended as whorl application only.

Parathion. Aerial application only. Do not substitute me-thyl parathion.

Phorate. Do not place in contact with seed at planting.Apply only once after plant emergence.

tion and development are hindered. Mois-ture-stressed sorghum plants are morelikely than non-stressed plants to be dam-aged by corn leaf aphids. Although very

rare, infestations on seedling sorghummight cause stand loss, and grain head in-festations might cause harvesting problems.

Because corn leaf aphids prefer to live andfeed in the whorl of sorghum, aphid num-bers normally decline rapidly after the grainhead exerts (emerges) from the boot. Some-times molds grow on the honeydew that cornleaf aphids produce. Honeydew on sorghumgrain heads has been associated with har-vesting problems. The aphid also transmitsmaize dwarf mosaic virus.

Although insecticide is rarely justified, cornleaf aphid can be controlled with the insecti-cides used for greenbug. Gaucho®-treated seedor carbofuran, disulfoton, phorate or terbufosat planting are effective in controlling corn leafaphids. However, corn leaf aphids do not in-ject toxin as they feed and very rarely dam-age sorghum. Because it is rarely a pest, sam-pling procedures and damage assessment in-formation are unavailable.

GreenbugSchizaphis graminum

The greenbug is anaphid that sucks plantjuices and injects toxininto sorghum plants. Theadult greenbug is lightgreen, approximately1/16 inch long, with acharacteristic darkergreen stripe down theback. Usually, the tips ofthe cornicles and leg seg-ments farthest from thebody are black. Wingedand wingless forms maybe present in the samecolony.

Females produce living young (nymphs)without mating. Under optimum conditions,the life cycle is completed in 7 days. Eachfemale produces about 80 offspring duringa 25-day period.

Greenbugs feed in colonies on the under-side of leaves and produce much honeydew.The greenbug may be a pest during the seed-ling stage and in the boot or heading stage.

Infestations may be detected by the appear-ance of reddish leaf spots caused by the toxingreenbugs inject into the plant. The red-dened areas enlarge as the number of green-bugs and injury increase. Damaged leavesbegin to die, turning yellow then brown.Damage at the seedling stage may result instand loss.

Larger sorghum plants tolerate moregreenbugs. Yield reductions during boot, flow-ering and grain-development stages dependon greenbug numbers, length of time green-bugs have infested the plants, and generalplant health. Many greenbugs on booting andolder plants can reduce yields and weakenplants that may later lodge.

Scouting sorghum for greenbugs is easy.Examine a minimum of 40 randomly selectedplants per field each week. Greenbugs are sel-dom distributed evenly in a field, so examineplants from all parts of the field; avoid exam-ining only field borders. In fields larger than80 acres, or if making a control decision isdifficult, examine more than 40 plants.

When deciding whether to control green-bugs, consider the amount of leaf damage,number of greenbugs per plant, percentageof parasitized greenbugs (mummies), num-bers of greenbug predators (lady beetles) perplant, moisture conditions, plant size, stageof plant growth and overall condition of thecrop. It is important to know from week toweek whether greenbug numbers are in-creasing or decreasing. For example, insec-ticide treatment would not be justified if therecommended treatment level (based on leafdamage) had been reached but greenbugnumbers had declined substantially fromprevious observations.

In seedling sorghum (less than 6 inchestall), greenbugs may be found on any partof the plant including the whorl or in thesoil at the base of the plant. When scoutingseedling sorghum, examine the entire plantand the soil around the base of the plant.Note the presence or absence of greenbugsand any damage to plants (yellowing, deathof tissue). Refer to Table 10 for economicthresholds for greenbugs on different plantgrowth stages.

13

Greenbug

Plants can tolerate about 30 percent leafloss before yield is reduced. Greenbug in-festations after sorghum flowering and be-fore the hard-dough stage should be con-trolled before they kill more than two nor-mal-sized leaves on 20 percent of the plants.In the Texas Blacklands, insecticide appli-cation is suggested when greenbugs arecolonizing the upper leaves of booting sor-ghum and causing red spotting or yellow-ing of leaves.

These guidelines are based on the as-sumption that greenbugs are increasing sorapidly that control by beneficial insects isineffective. However, when more than 20percent of the greenbugs appear brown andswollen from being parasitized, an insecti-cide treatment is usually unnecessary. Also,plants showing drought or other stress can-not tolerate as much greenbug damagewithout suffering reduction in yield.

Greenbug colonies usually begin on theunderside of lower leaves and move up theplant. On most sorghum hybrids, only theunderside of lower leaves need to be exam-ined, although in some cases greenbug colo-nies may be found first on the underside ofupper leaves. Do not confuse greenbugswith the bluish green corn leaf aphid, oftenfound with greenbugs in the plant whorl.

Greenbugs in a field can increase 20-foldper week, but the seasonal average is 5- to6-fold increase each week. Rain and preda-tors suppress aphid abundance early in theseason, although the increase of natural en-

emies has a lag time of 1 to 2 weeks. A com-mon parasitoid usually is responsible for arapid decline in aphid abundance late in theseason.

Sorghum hybrids resistant to greenbugare available commercially. However, green-bug biotypes have consistently occurred andnew resistant hybrids have had to be de-veloped. Hybrids resistant to greenbug bio-types C, E, I and K have been or are beingdeveloped. Using greenbug-resistant hy-brids is suggested. Resistance mainly istolerance, and therefore resistant hybridswill not be free of greenbugs. Damagethresholds for resistant sorghums are thesame as for susceptible sorghums becausethresholds are based on plant damage.

When deciding on insecticide treatment,consider the previously listed factors andconsult the recommended treatment levelsin Table 10. When estimating leaf damage,consider any leaf to be dead if more than75 percent of its surface is red, yellow, orbrown. Do not mistake for greenbug dam-age the natural senescence of the small bot-tom leaves. Estimate an average leaf dam-age level for the entire field unless it is fea-sible to spot treat areas of the field.

The greenbug usually is susceptible to la-beled insecticides (Table 11), but resistanceto organophosphorous insecticides exists inseveral counties in the Texas Panhandle.Continued extensive use of certain insecti-cides could expand the resistance problem.Where resistance exists in an area, applythe initial insecticide at the higher labeleddosage rate and increased application vol-ume to ensure complete coverage.

Chinch bugBlissus leucopterus leucopterus

Chinch bugs are spo-radic pests of sorghum inTexas. Adult chinch bugsare black, with reddishyellow legs and with con-spicuous, fully developedwhite forewings, each ofwhich has a black trian-gular spot at the middle

14

Table 10. Economic threshold levels for greenbug on sor-ghum at different plant growth stages.

Plant size When to treat

Emergence to 20% of plants visibly damagedabout 6 inches (beginning to yellow), with greenbugs

on plants

Larger plant Greenbug colonies causing redto boot spotting or yellowing of leaves and

before any entire leaves on 20% ofplants are killed

Boot to At death of one functional leaf onheading 20% of plants

Heading to When greenbug numbers are sufficienthard dough to cause death of two normal-sized

leaves on 20% of plants

Chinch bug

of the outer margin. Immature chinch bugsresemble adults in shape but lack wings.Young nymphs are yellowish, later turningreddish with a white or pale yellow bandacross the front part of the abdomen. Oldernymphs are black and gray with a conspicu-ous white spot on the back between the wingpads.

Eggs are laid behind the lower leaf sheathsof sorghum plants, on roots or in the groundnear the host plant. The life cycle is completedin 30 to 40 days, and there are at least twogenerations a year. Chinch bugs overwinteras adults in bunch grass. They begin movingto sorghum when temperatures reach 70° F.

Adult and immature chinch bugs suckjuices from stems, leaves or underground

15

Table 11. Suggested insecticides for controlling greenbug.





Chlorpyrifos See remarks (Lorsban® 4E) 8-32 oz./acre 30-60 30-60

Dimethoate See remarks (4E) 8-16 oz./acre 28 28 (5E) 6.4-12.8 oz./acre 28 28

Disulfoton See remarks (Di-Syston®) (8E) 4-8 oz./acre 07 45 (15G) 5.0-6.7 lb./acre 30 45

Malathion (57EC) 24 oz./acre

Parathion (ethyl) See remarks (4E) 8-16 oz./acre 12 12 (8E) 4-8 oz./acre 12 12

Phorate See remarks (Thimet®) (15G) 6.7 lb./acre 30 30 (20G) 4.9 lb./acre 30 30

RemarksAldicarb. Do not feed green forage to livestock.

Carbofuran. Applicator must use proper protective equipment when applying this highly toxic insecticide. Do not apply afterheads emerge from the boot.

Chlorpyrifos. Do not exceed three applications. The waiting period from last application to harvest or grazing is 30 days forthe 16-oz. rate and 60 days for more than 16 oz.

Dimethoate. Do not apply more than three times per season. Do not apply after heads emerge from the boot.

Disulfoton. 8E - Do not apply foliar spray or granules more than three times per crop season. Post-harvest interval is 34 days forthree foliar applications. 15G - Granular formulation applied post emergence is recommended as whorl application only.

Parathion. Aerial application only. Do not substitute methyl parathion.

Phorate. Do not place in contact with seed. Do not feed foliage before grain harvest.

Terbufos. May be knifed in at bedding, or banded (except in West Texas) or knifed in at planting (see label for dosage differ-ences). Do not place granules in direct contact with seed. For early season control of light to moderate infestations.





Applied at planting

Aldicarb See remarks (Temik® 15G) 7 lb./acre 90


Disulfoton (Di-Syston®) (8E) 1.2 oz./1,000

ft. of row (15G) 6-8 oz./1,000

ft. of row

Phorate See remarks (Thimet®) (15G) 8 oz./1,000 30 30

ft. of row (20G) 6 oz./1,000 30 30

ft. of row

Terbufos See remarks (Counter® 15G) 8-16 oz./1,000

ft. of row (Counter® 20CR®) 6-12 oz./1,000 100 50

ft. of row

plant parts. Young plants are highly sus-ceptible. Older plants withstand attack bet-ter, but they, too, become reddened, weak-ened and stunted. Chinch bugs are favoredby hot, dry weather, and large numbers ofimmature bugs often migrate from wildbunch grasses or small grains to congregateand feed behind lower leaf sheaths of sor-ghum plants.

To find chinch bugs, carefully examineplants and surrounding soil. Make at leastfive random checks per field.

Cultural practices that stimulate dense,vigorous plant stands are recommendedbecause these conditions are less favored bychinch bugs, and injury usually is reduced.Plant sorghum as early as practical.

Apply insecticide when two or more chinchbugs are found on 20 percent of seedlingplants less than 6 inches tall. On tallerplants, insecticide often is justified whenchinch bugs infest 75 percent of the plants.Generally, one chinch bug per seedling sor-ghum plant reduces grain yield by 2 per-cent.

Chinch bugs sometimes are difficult tocontrol with insecticides. In fields with ahistory of economically damaging infesta-tions of chinch bug, at-planting, soil-incor-porated insecticides or Gaucho®-treatedseed may be justified. Granular insecticidesmust receive about one-half inch of rainfallafter application to effectively suppressearly-season chinch bug infestations.

16

Table 12. Suggested insecticides for controlling chinch bug.




Carbaryl See remarks (Sevin®) (4F) 32-64 oz./acre 21 14 (80S or 80WSP) 1.25-2.5 lb./acre 21 14 (50W) 2-4 lb./acre 21 14 (4XLR+®) 32-64 oz./acre 21 14


Chlorpyrifos See remarks (Lorsban® 4E) 16-32 oz./acre 30-60 30-60

Cyfluthrin See remarks (Baythroid® 2E) 1.3-2.8 oz./acre 14

Cyhalothrin See remarks (Karate® 1E) 3.84 oz./acre





Applied at planting

Aldicarb 7.5 oz./1,000 See remarks (Temik® 15G) ft. of row 90

Chlorpyrifos 8 oz./1,000 (Lorsban®15G) ft. of row

Terbufos See remarks (Counter® 15G) 8 oz./1,000

ft. of row (Counter® 20CR®) 6 oz./1,000 100 50

ft. of row

RemarksAldicarb. Apply granules in furrow and cover with soil. Do not feed green forage to livestock.

Carbaryl. Use high-gallonage ground application directed at bases of plants.

Carbofuran. Ground application only. Use 20-30 gallons of water per acre. Do not apply more than twice per season. Do notapply after heads emerge from the boot.

Chlorpyrifos. Apply with enough water to ensure a minimum spray volume of 20-40 gallons per acre. Use ground equipmentto direct spray toward bases of plants. The waiting period from last application to harvest or grazing is 30 days for the 16-oz.rate and 60 days for more than 16 oz. Do not apply more than 48 oz. per acre per season. Do not treat sweet sorghum.

Cyfluthrin. If one or two applications are made, green forage may be fed or grazed on the day of treatment. If threeapplications are made, allow at least 14 days between last application and grazing. Direct applications at the basal portionof the plant.

Cyhalothrin. Do not graze livestock in treated area or harvest for fodder, silage or hay.

Terbufos. Apply in 5- to 7-inch band over the row in front of or behind press wheel and lightly incorporate into soil. Do notplace granules in direct contact with seed. For early-season control of light to moderate infestations.

If infestations reach the economic thresh-old after plant emergence, apply post-emer-gence insecticide using at least 20 gallons ofwater per acre through nozzles directed at thebases of plants. Control is seldom satisfactoryon plants in the boot stage or later. Aerial in-secticide application is seldom effective andnot suggested.

Corn earworm and fall armyworm(whorlworms)Helicoverpa zea and

Spodoptera frugiperda

Corn earworm and fallarmyworm infest thewhorls and grain heads ofsorghum plants. Larvaehatching from eggs laidon sorghum leaves beforegrain heads are availablemigrate to and feed ontender, folded leaves inthe whorl.

To find larvae in sor-ghum whorls, pull thewhorl leaf from the plantand unfold it. Frass, orlarval excrement, is pre-sent where larvae feedwithin the whorl. Dam-aged leaves unfoldingfrom the whorl are raggedwith “shot holes.” Al-though this may look dra-

matic, leaf damage usually does not reduceyields greatly, and control of larvae duringthe whorl stage is seldom economically jus-tified. Also, larvae within the whorl aresomewhat protected from insecticide.

Insecticide application may be justified iflarval feeding reduces leaf area by more than30 percent or is damaging the developinggrain head or growing point within the whorl.See the section on Corn earworm and fall ar-myworm (headworms) for information onthese insects as pests of sorghum grain heads.

Banks grass miteOligonychus pratensis

Large numbers of Banks grass mites some-times occur on sorghum, especially in more

arid areas of Texas. Thesemites are very small; fe-males are larger thanmales. After feeding,mites turn deep green, ex-cept for the mouthpartsand first two pairs of legsthat remain light salmoncolored. Eggs (about 50per female) are laid inwebbing on the undersideof sorghum leaves. Eggs are pearly white,spherical, one-fourth the size of the adultsand hatch in 3 to 4 days. The life cycle re-quires about 11 days under favorable con-ditions.

Spider mites suck juices from the under-side of sorghum leaves. Mite infestationsbegin along the midrib of the lower leaves.Infested areas become pale yellow initiallyand later become reddish on the top sur-face. The entire leaf may turn brown. Asspider mites become more abundant on thelower leaves, the infestation spreads up-ward through the plant. The underside ofheavily infested leaves has a dense depositof fine webbing spun by the spider mites.

Increases in spider mite abundance gen-erally occur after sorghum grain headsemerge. Large numbers of spider mites oc-curring early in kernel development canreduce the ability of sorghum plants to makeand fill grain. After kernels reach harddough, grain is not affected. However, highspider mite abundance may cause sorghumplants to lodge, resulting in harvest losses.

Inspect the underside of lower leavescarefully. Mites occur in colonies, first alongmidribs of leaves, but later spread awayfrom the midrib and up the plant to higherleaves. Webbing indicates the presence ofmites. Mite infestations commonly beginalong field borders, and may spread quicklythroughout a field.

Hot, dry weather may favor a rapid in-crease in mite abundance. Also, mites in sor-ghum may respond as induced (secondary)pests after an insecticide application for akey insect pest such as greenbug. Rapid in-creases in spider mite abundance after in-secticide application is thought to be caused

17

Corn earworm

Fall armyworm

Banks grass mite

by tolerance of mites to some insecticides,destruction of beneficial insects and dis-persal of mites from colonies.

Natural enemies do not always control spi-der mites adequately. Because spider mitesincrease more rapidly on moisture-stressedplants, irrigation, where available, should betimed to prevent plant stress. Also, spidermites may move from small grains, especiallywheat, to sorghum. To avoid direct infesta-tion by mites moving from small grains, plantsorghum away from small grains.

Insecticides produce varying degrees ofsuccess. Historically, insecticidal control ofmites in sorghum has been erratic. Insecti-cide application may be justified when 30percent of the leaf area of most sorghumplants in a field show some damage symp-toms from mite feeding. Thorough coverageis required; apply at least 3 to 5 gallons ofspray mixture per acre. Banks grass mitesare often resistant to insecticides.

Grain head insect pests

Sorghum midgeStenodiplosis sorghicola

The sorghum midge isone of the most damaginginsects to sorghum inTexas, especially in thesouthern half of the state.The adult sorghummidge is a small, fragile-looking, orange-red flywith a yellow head,brown antennae and legsand gray, membranouswings.

During the single day ofadult life, each female lays about 50 yellow-ish white eggs in flowering spikelets of sor-ghum. Eggs hatch in 2 to 3 days. Larvae arecolorless at first, but when fully grown, aredark orange. Larvae complete developmentin 9 to 11 days and pupate between the spike-let glumes. Shortly before adult emergence,the pupa works its way toward the upper tipof the spikelet. After the adult emerges, theclear or white pupal skin remains at the tipof the spikelet.

A generation is completed in 14 to 16 daysunder favorable conditions. Sorghum midgenumbers increase rapidly because of mul-tiple generations during a season and whensorghum flowering times are extended bya range of planting dates or sorghum ma-turities.

Sorghum midges overwinter as larvae incocoons in spikelets of sorghum or john-songrass. Johnsongrass spikelets contain-ing diapausing larvae fall to the ground andbecome covered with litter. When sorghumis shredded, spikelets containing larvae fallto the ground and are disked into the soil.Sorghum midges emerging in spring do sobefore flowering sorghum is available, andthese adults infest johnsongrass. Sorghummidges developing in johnsongrass disperseto fields of sorghum when it flowers.

Early-season infestations in sorghum areusually below damaging levels. As the sea-son progresses, sorghum midge abundance

18

Table 13. Suggested miticides for controlling Banksgrass mite.

Miticide Days from last(listed alphabetically) application to:


Dimethoate See remarks (4E) 16 oz. 28 28 (5E) 12.8 oz. 28 28

Disulfoton (Di-Syston® 8E) 8 oz. 07 45

Phorate See remarks (20G) 4.9 lb. 28

Propargite See remarks (Comite® 6.55E) 24-32 oz. 30

RemarksDimethoate. Ground application: Apply in 25-40 gallonsof water. Do not apply more than three times per sea-son. Do not apply after heads emerge from the boot.Do not use in the Trans-Pecos area.Phorate. Broadcast into whorl of plant. Do not use in theTrans-Pecos area.Propargite. Do not apply more than once per season.Slight phytotoxicity may occur on some sorghum hybrids.

Sorghum midge

increases, especially when flowering sor-ghum is available in the area. Numbers of-ten drop late in the season.

Sorghum midge damages sorghum whenthe larva feeds on a newly fertilized ovary,preventing normal kernel development.Grain loss can be extremely high. Glumesof a sorghum midge-infested spikelet fittightly together because no kernel develops.Typically, a sorghum grain head infested bysorghum midges has various proportions ofnormal kernels scattered among non-ker-nel-bearing spikelets, depending on the de-gree of damage.

Effective control of sorghum midge re-quires integration of several practices thatreduce sorghum midge abundance and po-tential to cause crop damage. The most ef-fective cultural management method foravoiding damage is early, uniform plantingof sorghum in an area so flowering occursbefore sorghum midge reach damaging lev-els. Planting hybrids of uniform maturityearly enough to avoid late flowering of grainheads is extremely important. This prac-tice allows sorghum to complete floweringbefore sorghum midges increase to damag-ing levels.

Cultural practices that promote uniformheading and flowering in a field also areimportant in deciding on treatment and inachieving acceptable levels of insecticidalcontrol. To reduce sorghum midge abun-dance, use cultivation and/or herbicides toeliminate johnsongrass inside and outsidethe field. Where practical, disk and deepplow the previous year’s sorghum crop todestroy overwintering sorghum midges.Use sorghum midge-resistant hybrids ifthey are available.

Multiple insecticide applications are usedto kill adults before they lay eggs. Sorghumplanted and flowering late is especially vul-nerable to sorghum midge. To determinewhether insecticides are needed, evaluatecrop development, yield potential and sor-ghum midge abundance daily during sor-ghum flowering. Because sorghum midgeslay eggs in flowering sorghum grain heads(yellow anthers exposed on individual spike-lets), they can cause damage until the entire

grain head or field of sorghum has flowered.The period of susceptibility to sorghum midgemay last from 7 to 9 days (individual grainhead) to 2 to 3 weeks (individual field), de-pending on uniformity of flowering.

To determine if adult sorghum midges arein a sorghum field, check at mid-morningwhen the temperature warms to approxi-mately 85° F. Sorghum midge adults aremost abundant then on flowering sorghumgrain heads. Because adult sorghum midgeslive less than 1 day, each day a new broodof adults emerges. This fact requires sam-pling almost daily during the time sorghumgrain heads are flowering. Sorghum midgeadults can be seen crawling on or flyingabout flowering sorghum grain heads.

The simplest and most efficient way todetect and count sorghum midges is to in-spect carefully and at close range all sidesof randomly selected flowering grain heads.Handle grain heads carefully during inspec-tion to avoid disturbing adult sorghummidges. Other sampling methods can beused, such as placing a clear plastic bag orjar over the sorghum grain head as a trap-ping device for adults.

Because they are relatively weak fliersand rely on wind currents to aid their dis-persal, adult sorghum midges usually aremost abundant along edges of sorghum

Figure 3. Estimated latest sorghum flowering dates most likelyto escape significant damage by sorghum midge.

19

May 10

May 26

June 5

June 10

June 20

June 30

August 1

fields. For this reason, inspect plants alongfield borders first, particularly those down-wind of earlier flowering sorghum orjohnsongrass. If no or few sorghum midgesare found on sorghum grain heads alongfield edges, there should be little need tosample the entire field.

However, if you find more than one sor-ghum midge per flowering grain head inborder areas of a sorghum field, inspect atleast 40 more grain heads from the entirefield (avoiding plants within 150 feet of fieldborders). Calculate the average number ofsorghum midge per flowering grain head.Sample at least 20 flowering grain headsfor each 20 acres in a field.

Base the need for insecticide treatmenton the number of adult sorghum midges perflowering grain head after at least 20 per-cent of the grain heads in a field are flower-ing. Tables 14 and 15 present economic in-jury levels for susceptible or resistant sor-ghum hybrids. (See page 5 for an explana-tion of economic threshold tables.)

Insecticide residues should effectively sup-press sorghum midges 1 to 2 days after treat-ment. However, if adults still are present 3to 5 days after the first application of insec-ticide, immediately apply a second insecti-cide treatment. Several insecticide applica-tions at 3-day intervals may be justified ifyield potential is high and sorghum midgesexceed the economic injury level.

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Table 14. Economic injury levels based on number ofadult sorghum midges per flowering grain head of asusceptible sorghum hybrid.


Number of sorghum midges

6 2.4 2.0 1.6 1.3 1.2 1.1 0.9 0.8 0.8

8 3.0 2.5 2.2 1.8 1.6 1.4 1.2 1.1 1.1

10 3.5 3.0 2.6 2.2 1.9 1.7 1.5 1.4 1.3

12 3.9 3.5 3.1 2.7 2.3 2.0 1.8 1.6 1.4

Table 15. Economic injury levels based on number ofadult sorghum midges per flowering grain head of aresistant sorghum hybrid.


Number of sorghum midges

6 12 10 8 7 6 6 5 4 4

8 15 13 11 9 8 7 6 5 5

10 17 15 13 11 10 9 8 7 6

12 19 17 15 13 11 10 9 8 7

Table 16. Suggested insecticides for controlling sor-ghum midge.



Chlorpyrifos (Lorsban® 4E) 8 oz. 30 30

Cyfluthrin See remarks (Baythroid® 2E) 1.0-1.3 oz. 14

Cyhalothrin See remarks (Karate® 1E) 1.92-2.56 oz.

Malathion (Fyfanon® ULV) 8-12 oz. 07 07

Methomyl (Lannate®) (2.4LV) 12-24 oz. 14 14 (90WSP) 4-8 oz. 14 14


RemarksCyfluthrin. If one or two applications are made, greenforage may be fed or grazed on the day of treatment. Ifthree applications are made, allow at least 14 days be-tween last application and grazing.



Corn earworm and fall armyworm(headworms)Helicoverpa zea and

Spodoptera frugiperda

Corn earwormand fall army-worm moths layeggs on leaves orgrain heads ofsorghum. Newlyhatched corn earworm larvae are pale incolor and only 1/8 inch long. They grow rap-idly and become variously colored, rangingfrom pink, green or yellow to almost black.Many are conspicuously striped. Down theside is a pale stripe edged above with a darkstripe. Down the middle of the back is a darkstripe divided by a narrow white line thatmakes the dark stripe appear doubled. Fullygrown larvae are robust and 1 1/2 to 2 incheslong.

Young fall armyworm larvae are green-ish and have black heads. Mature larvaevary from greenish to grayish brown andhave a light-colored, inverted, Y-shaped su-ture on the front of the head and dorsal lineslengthwise on the body.

Corn earworm and fall armyworm larvaefeed on developing grain. Small larvae feedon flowering parts of the grain head at first,then hollow out kernels. Larger larvae con-sume more kernels and cause most damage.The last two larval stages cause about 80percent of the damage. Frass is common ininfested grain heads, on tops of upper leavesand on the ground under plants. Under cer-tain conditions, infested grain heads mayhave molds.

Natural mortality of small corn earwormand fall armyworm larvae is normally veryhigh. Both corn earworm and fall army-

worm moths can lay several hundred eggson sorghum grain heads before or duringflowering, but only a few larvae survive.Natural factors suppressing these insectsinclude predators, parasites, pathogens andcannibalism among larvae.

Infestations usually are less in early-than late-planted sorghum. An importantmanagement tactic is to use sorghum hy-brids with loose (open) grain heads. Early-planted sorghum and hybrids with opengrain heads usually are less infested.

Begin inspecting sorghum grain headssoon after flowering and continue at 5-dayintervals until hard dough. To examine grainheads for corn earworms and fall armyworms,shake randomly selected grain heads vigor-ously into a 5-gallon bucket, where larvae canbe seen and counted easily. This “beat-bucket”technique permits detection of even small lar-vae (less than 1/4 inch) commonly overlookedduring visual inspection of the grain head.Inspect at least 30 grain heads from a fieldto ensure reasonable reliability of samplesize. Sample at least one grain head per acrein fields larger than 40 acres.

Because many young headworm larvaedie naturally, do not apply insecticide untilthey are at least 1/2 inch long. The economicinjury level is about 1 to 2 larvae per grainhead of commercial sorghum (Table 17).(See economic threshold level discussion onpage 5.) Fewer larvae per grain head mayjustify treatment on sorghum grown forseed because of the higher per-acre value.Table 18 lists insecticides suggested to con-trol headworms.

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Table 17. Economic injury levels based on number of cornearworm and fall armyworm larvae per sorghum grain head.


Number of headworms

6 1.5 1.2 1.0 0.9 0.8 0.7 0.6 0.6 0.5

8 2.0 1.6 1.3 1.1 1.0 0.9 0.8 0.8 0.7

10 2.5 2.0 1.6 1.4 1.2 1.1 1.0 1.0 0.9

12 3.0 2.4 1.9 1.7 1.5 1.4 1.3 1.2 1.1

Corn earworm

Fall armyworm

dish brown, slender and sub-cylindrical. Ageneration requires 1 month; as many as sixgenerations may develop in a year. The larvaoverwinters in a cocoon on the host plant.

Many sorghum webworms may be foundin grain heads of late-planted sorghum.Young larvae feed on developing flowerparts. Older larvae gnaw circular holes inand feed on the starchy contents of matur-ing kernels, which usually are only partlyconsumed. Each larva may eat more than12 kernels in 24 hours. Larvae do not spinwebs (as the name might imply) over thesorghum grain head but, when disturbed,young larvae often suspend themselves byspinning a thin silken thread.

Inspect for sorghum webworms whengrain heads begin to flower; continue at 5-day intervals until kernels are in the hard-dough stage. To examine grain heads for sor-ghum webworms, shake grain heads vigor-ously into a 5-gallon plastic bucket, where

Sorghum webwormNola sorghiella

Sorghum webwormsoccasionally infest grainheads of sorghum planted2 to 3 weeks later thannormal. This insect oc-curs primarily in themore humid eastern halfof Texas.

Adults are small, whitemoths active at night.They lay about 100 eggssingly but fastened rather

securely to flowering parts or kernels of sor-ghum. Eggs are round to broadly oval andare flattened from top to bottom.

Webworm larvae are somewhat flattened,yellowish or greenish brown and marked withfour lengthwise reddish to black dorsalstripes. When mature, larvae are about 1/2inch long and covered with many spines andmuch hair. Pupae within a cocoon are red-

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Table 19. Suggested insecticides for controllingsorghum webworm.



Carbaryl (Sevin®) (4F) 32-64 oz. 21 14 (80S or 80WSP) 1.25-2.5 lb. 21 14 (50W) 2-4 lb. 21 14 (4XLR+®) 32-64 oz. 21 14



Methomyl (Lannate®) (2.4LV) 24 oz. 14 14 (90WSP) 8 oz. 14 14


RemarksCyfluthrin. If one or two applications are made, greenforage may be fed or grazed on the day of treatment. Ifthree applications are made, allow at least 14 days be-tween last application and grazing.



Table 18. Suggested insecticides for controlling corn ear-worm and fall armyworm in sorghum.



Carbaryl (Sevin®) (4F) 32-64 oz. 21 14 (80S or 80WSP) 1.25-1.8 lb. 21 14 (50W) 2-4 lb. 21 14 (4XLR+®) 32-64 oz. 21 14



Methomyl (Lannate®) (2.4LV) 12-24 oz. 14 14 (90WSP) 4-8 oz. 14 14

Parathion (ethyl) See remarks (4E) 12-16 oz. 12 12 (8E) 6-8 oz. 12 12

RemarksCyfluthrin. If one or two applications are made, green for-age may be fed or grazed on the day of treatment. If threeapplications are made, allow at least 14 days between lastapplication and grazing.Cyhalothrin. Do not graze livestock in treated area or har-vest for fodder, silage or hay.Parathion. Aerial application only. Do not substitute methylparathion.

Sorghum webworm

even small larvae can be seen and countedeasily. Inspect at least 30 plants from a fieldto ensure that sample estimates are reason-ably reliable. Sample at least one grain headper acre in fields larger than 40 acres.

Insecticide application is economicallyjustified when grain heads are infested withan average of five or more small larvae. Cul-tural practices to reduce sorghum webwormabundance include plowing sorghum resi-dues after harvest to destroy overwinteringpupae, planting as early as practical andusing sorghum hybrids with loose (open)grain heads.

Grain head-feeding bugsSeveral species of true bugs, primarily

stink bugs, may move in relatively large num-bers from alternate host plants into sorghumduring kernel development. Bugs infestingsorghum in Texas include rice stink bug,southern green stink bug, conchuela stinkbug, brown stink bug (Euschistus servus), red-shouldered stink bug (Thyanta accerra),leaffooted bug and false chinch bug.

Conchuela stink bug

The conchuela stink bug (Chlorochroaligata) varies in color from dull olive or ashgray to green, purplish pink, or reddishbrown. The most characteristic markingsare orange-red bands along the lateral mar-gins of the thorax and wings and a spot ofthe same color on the back at the base ofthe wings.

23

The rice stink bug (Oebalus pugnax) isstraw-colored, shield-shaped and 1/2 inchlong. Females lay about 10 to 47 short, cy-lindrical, light-green eggs in a cluster of tworows. Eggs hatch after 5 days, and nymphsrequire 15 to 28 days to become adults.

Southern green stink bug

Rice stink bug

The southern green stink bug (Nezaraviridula) is about 3/4 inch long, green andsomewhat shield-shaped. Females deposit300 to 500 eggs in clusters of about 30. Theeggs hatch in about 7 days, reaching theadult stage in about 6 weeks.

Leaffooted bug

The leaffooted bug (Leptoglossus phyllo-pus) is brown, oblong and just longer than3/4 inch. A white band extends across thefront wings. The lower part of each hind legis dilated or leaf-like. Eggs are laid in rowsof 15 to 35. Nymphs are reddish.

False chinch bug

The false chinch bug (Nysius raphanus)resembles the chinch bug but with more uni-form color, ranging from gray to brown.False chinch bugs are 1/10 inch long. Mul-titudes of the insect occasionally migratefrom wild hosts, such as wild mustard, tosorghum, but these insects usually concen-trate in small areas of a field.

Bugs suck juices from developing sor-ghum kernels and, to a lesser extent, fromother grain head parts, and may cause eco-nomic damage. The extent of damage de-pends on number of bugs per grain head,

duration of infestation, and stage of kerneldevelopment when infestation occurs. Bugscause more damage early during kerneldevelopment and less as grain develops tothe hard-dough stage. Both nymphs andadults can reduce grain weight, size andseed germination. Fungi often infect dam-aged kernels, causing them to turn blackand further deteriorate in quality. Damagedkernels rarely develop fully and may be lostduring harvest.

Grain head-feeding bugs tend to congre-gate on sorghum grain heads and some-times within areas of a field. Use the beat-bucket technique to estimate abundance.Shake sorghum grain heads vigorously intoa 5-gallon bucket, where bugs can be seenand counted more easily. However, adultbugs will fly from the sampled plant or thebucket. Count those that fly from sorghumgrain heads or from the bucket and thoseon plant leaves. Sample at least 30 plantsfrom a field. Take at least one sample peracre in fields larger than 40 acres.

To determine the profitability of control-ling an infestation of rice, southern green,or conchuela stink bugs or of leaffooted bugs,consult economic injury Tables 20 through23. (See economic threshold level discussionon page 5.) The number of bugs per sorghumgrain head that will reduce grain yield var-ies depending on bug species and stage ofgrain development when infestation occurs.Determine the grain development stage attime of sampling and refer to the appropri-ate table. If the grain development stage ishard dough and the infestation per grainhead is 16 or fewer bugs, an insecticide ap-plication likely is unjustified. The economicthreshold level for false chinch bug is 140bugs per grain head when infestation beginsat the milk stage of grain development.

Not all stink bug species in sorghum areeconomic pests. Several species, such as thespined soldier bug, prey on harmful insectsand thus are beneficial.

For more information on grain head-feed-ing insects, see B-1421, Suggested Guide forControlling Panicle-Feeding Bugs in TexasSorghum.

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Table 20. Economic injury level based on number of ricestink bugs per sorghum grain head beginning at the milkstage of kernel development.


Number of rice stink bugs

6 7 6 6 5 5 5 4 4 4

8 8 7 6 6 6 5 5 4 4

10 8 8 7 7 6 6 6 5 5

12 9 8 8 7 7 6 6 5 5

Table 21. Economic injury level based on number of ricestink bugs per sorghum grain head beginning at thesoft-dough stage of kernel development.


Number of rice stink bugs

6 9 8 8 7 7 6 6 6 5

8 10 9 9 8 8 7 7 7 6

10 12 10 10 9 9 8 8 7 7

12 13 12 11 10 10 9 9 8 8

Table 23. Economic injury level based on number of adultsouthern green stink bugs, conchuela stink bugs andleaffooted bugs per sorghum grain head beginning at thesoft-dough stage of kernel development.


Number of bugs

6 8 7 7 6 6 5 5 4 4

8 9 8 7 7 7 6 6 5 5

10 10 9 8 8 7 7 6 6 5

12 11 10 9 9 8 8 7 7 6

Table 22. Economic injury level based on number of adultsouthern green stink bugs, conchuela stink bugs andleaffooted bugs beginning at the milk stage of kerneldevelopment.


Number of bugs

6 5 4 4 4 4 3 3 3 2

8 5 5 5 4 4 4 4 3 3

10 6 6 5 5 5 4 4 4 3

12 6 6 6 5 5 5 4 4 4

Stem-boring insect pests

Sugarcane borerDiatraea saccharalis,Southwestern corn borerDiatraea grandiosella,Neotropical borerDiatraea lineolata andMexican rice borerEoreuma loftini

These closely relatedinsects tunnel in thestalks of sorghum, cornand other crops. The bi-ology of these four speciescan be generalized: Whiteto buff-colored adultmoths lay clusters of el-liptical to oval shaped,flattened eggs that over-

lap like fish scales in shingle-like arrange-

ments on leaves of host plants. Eggs hatchin 3 to 7 days.

The larval stage lasts about 25 days andthe pupal stage about 10. There are two tothree generations a year. Larvae are creamywhite, about 1 inch long when fully grown,and most body segments have conspicuousround brown or black spots. Spots arelighter colored or absent on mature over-wintering larvae. Most stem-boring insectspass the winter as fully grown larvae in cellsinside stalks that remain after the crop isharvested.

Young larvae feed for a few days on leavesor the leaf axis. Older larvae tunnel into thesorghum stalks. Larvae bore up and downthe pith of the stalk. Borer-infested stalksmay be reduced in diameter, and lodging ofinfested plants can result. Boring by larvaein the stem just below the grain head cancause it to break and the grain head to fall.Injury by borers makes the plant more sus-ceptible to stalk rot diseases.

Planting sorghum early is important be-cause borers typically are more abundantin late-planted sorghum. Shredding stalksvery close to the ground or plowing anddisking stubble destroys overwintering lar-vae by exposing them to cold temperaturesin more northern regions of Texas. Thispractice reduces borer abundance the nextyear. Insecticidal control rarely is justified.

To determine the presence of stem borers,examine the sorghum plants carefully. Smallholes near the leaf axis indicate that a larvahas entered the stalk. Once larvae have en-tered the stalk, stalks must be split to seethe larvae. Inspect leaves carefully, becauseeggs are hard to find. Clusters containing10 to 20 individual eggs may be on the topor underside of leaves, depending on theborer species. Assess the abundance of eggsand small larvae before larvae bore intostalks. Insecticidal control is effective, onlyif applied before larvae bore into stalks.Karate and Sevin are labeled for controllingsouthwestern corn borer in sorghum.

25

Table 24. Suggested insecticides for controlling grainhead-feeding bugs.



Carbaryl See remarks (Sevin®) (4F) 32-64 oz. 21 14 (80S or 80WSP) 1.25-2.5 lb. 21 14 (50W) 2-4 lb. 21 14 (4XLR+®) 32-64 oz. 21 14



Parathion (ethyl) See remarks (4E) 12-16 oz. 12 12 (8E) 6-8 oz. 12 12

RemarksCarbaryl. Direct spray into heads for optimum control.

Cyfluthrin. If one or two applications are made, greenforage may be fed or grazed on the day of treatment. Ifthree applications are made, allow at least 14 days be-tween last application and grazing.



Sugarcane borer

Lesser cornstalk borerElasmopalpus lignosellus

Larvae of the lessercornstalk borer attackroots and bore into stalksof sorghum plants. Dam-aging infestations of thisinsect rarely occur in sor-ghum. Larvae are lightbluish green with promi-

nent transverse reddish-brown bands. Theyfeed in silken tunnels covered with soil par-ticles. Larvae pupate in silken cocoons un-der crop debris.

Lesser cornstalk borer usually is more se-vere during dry periods and in sandy soils.Cultural practices that preserve moistureand increase organic matter in the soil dis-courage the insect. Early planting and ro-tation with nonhost crops help avoid dam-age from lesser cornstalk borer. Insecticidalcontrol rarely is justified.

Sugarcane rootstock weevilAnacentrinus deplanatus

The sugarcane root-stock weevil infests sor-ghum sporadically, espe-cially during dry yearsand in fields wherejohnsongrass is abun-dant.

The adult weevil isdark brown or black, about 1/8 inch long and1/16 inch wide. The insect overwinters asan adult on ground protected by plant resi-dues. Weevils in early spring infest wildgrasses, such as johnsongrass, and latermove to sorghum. The female uses hermouthparts to make a small puncture at thebase of the plant into which the egg is de-posited and concealed. About 16 eggs arelaid and hatch in 6 days. Larvae are white,legless grubs about 1/5 inch long when fullygrown. A generation is completed in about40 days.

Adult weevils feed on young sorghumplants and crowns. This damage is notice-able but not as serious as that caused bylarvae. Larvae tunnel into the sorghumstalk just below or above the surface of the

soil. Tunnels resemble those made by otherborers, except they are much smaller anddo not extend up the stalk. Larvae often arefound at nodes and near the outer surfacesof the stalk. Their feeding often is respon-sible for a drought-stressed appearance andlodging of sorghum plants. Exit holes andfeeding tunnels provide favorable areaswhere such pathogens as charcoal rot canenter the plant. Historically, control of thisinsect has not been required.

Policy statementInformation contained in this publication

on managing insect and mite pests of sor-ghum is based on the research and experi-ence of Texas Agricultural Extension Ser-vice and Texas Agricultural ExperimentStation entomologists. Suggested manage-ment strategies are believed to be reliable.However, it is impossible to eliminate allrisks associated with managing insect andmite pests in sorghum. Unexpected condi-tions or circumstances may result in lessthan satisfactory results when these sug-gestions are used. The Texas AgriculturalExtension Service and The Texas Agricul-tural Experiment Station do not assumeresponsibility for ineffective results fromusing information contained in this publi-cation. The user of the information in thispublication assumes all risk.

Insecticides and miticides listed in thispublication for use against insect and mitepests of sorghum must be registered and la-beled for use by the Environmental Protec-tion Agency and Texas Department of Agri-culture. The status of insecticide labelschange and may have changed since thispublication was printed. Extension ento-mologists and other appropriate specialistsare advised of changes in label status andmay be contacted for this information. TheUSER always is responsible for effects ofpesticide residues on livestock and crops,as well as problems that arise from drift ormovement of pesticide from the applicationsite to other areas. Always carefully readand follow the instructions on the pes-ticide label.

26

Lesser cornstalk borer

Sugarcane rootstalkweevil larva

The information given herein is for educational purposes only. Refer-ence to commercial products or trade names is made with the under-standing no discrimination is intended and no endorsement by the TexasAgricultural Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardlessof socioeconomic level, race, color, sex, religion, handicap or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress ofMay 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture.Edward A. Hiler, Interim Director, Texas Agricultural Extension Service, The Texas A&M University System.

10,000 copies, Revision ENT, AGR 15-2

Produced by Agricultural Communications, The Texas A&M University System

Original color images courtesy of “Sorghum Insect Photo CD,” compiled by Phil Sloderbeck,Kansas State University Department of Entomology, 1995; and Greg Cronholm, Bart Drees,John Jackman and George Teetes, Texas A&M University System.

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