Pests, Diseases And Disorders Of Sweet Corn

INSECTSNabisi spp.DESCRIPTIONBENEFITNymph: Similar to adultsexcept smaller and wingless.Nymphs and adults areaggressive predators onmany other insects includingaphids, leafhoppers, motheggs and small caterpillars.Adult: Slender, light tanbug 8–12 mm long withlong, prominent suckingmouthpart. Long legs,with front two strongerfor grasping prey.MOST COMMONAny time of year.Dried fruit beetleCarpophilus spp.DESCRIPTIONMOST COMMONLarvae: Tiny creamcoloured grub.During summer, especiallyif heliothis is notadequately controlled.Adult: Small (2–3 mmlong), oval-shaped blackto brownish beetles.Several different speciescan infest corn.INSECTSBeneficialinsectDamsel bugDAMAGEBeetles get inside cornhusks which have beenloosened due to damage byother insects (eg heliothis)or disease. They chewon the kernels and are acontamination issue.Damsel bug16Beetles in corn showing feeding damage17

Earwig — black fieldDESCRIPTIONDAMAGEUsually a minor pest thatNymph: Similar to adult butlighter in colour and with less feeds on decaying plantdeveloped wings and pincers. material. However, theycan also eat germinatingAdult: Dark brown to blackseeds and young plants andwith slender flattenedupper parts of corn roots.body up to 15 mm long andMOST COMMONbeaded antennae. Obviouspair of pincers at the end ofIn heavy, black soils and moistthe body which are curvedconditions. Nymphs tendin males and straighter into emerge during spring.females. Darker and smallerthan other earwig species.Labidura truncataBeneficialinsectDESCRIPTIONNymph: Similar to adult butsmaller and lighter coloured.Adult: Light brown, flattenedand segmented body upto 35 mm long with darkbrown patches and dark eyes.Large pincers on the tail,which are curved in malesand straighter in females. INSECTSINSECTSNala lividipesEarwig — brownBENEFITAttacks caterpillars and mothpupae, such as heliothis.MOST COMMONAny time of year.Adult male black field earwig (D Hobern); Black field earwig18Adult brown earwigs (J Wessels QDAF, A Henderson Minibeast Wildlife)19

INSECTSCermatulus nasalis20DESCRIPTIONBENEFITEgg: Cylindrical, black eggswith short white spineslaid in a neat raft of up to50 eggs on a leaf or stem.Nymphs and adults attacksoft bodied insects suchas heliothis caterpillars.Nymph: Early instars havebright red bodies with blackhead and legs. Later instarsdevelop bright red, orangeand black markings.Spring to summer.MOST COMMONGreen vegetable bugNezara viridulaDESCRIPTIONDAMAGEEgg: Neat rafts of barrelshaped, creamy eggs laidon leaf undersides, turninggolden as they mature.Sucks sap from youngshoots and directly fromdeveloping kernels. Feedingsites can become diseased.Nymph: Initially orangered, then darkening withbright red, green andwhite patterning. Tendto stay in groups.An occasional pest,most common duringspring and summer.INSECTSBeneficialinsectGlossy shield bugMOST COMMONAdult: Shield-shaped bugup to 12 mm long withbrown to black patterningand small light yellowmarkings. Obvious piercingand sucking mouthpart.Adult: Green, shield-shapedbug around 15 mm long.Glossy shield bug nymph (P Chew) and adult bug (C Harding MAF)Green vegetable bug eggs, nymph (A Ryland) and adult21

HeliothisDESCRIPTIONEgg: Ribbed white domes1 mm diameter laid singlyor in small groups. Darkento brown before hatching.Pupae: Golden brownand usually found justunder the soil surface. Rainstimulates emergence.Caterpillar: Initially 1.5 mmlong, light brown withdark heads. When theyreach around 15 mm longthey darken and developdistinctive stripes. Colourranges from brown togreenish or reddish. Upto 30–40 mm long.Adult: Stout moth with lightlypatterned brown wings heldflat across the body. Hindwings are pale with a darksection towards the margin.holes in leaves, holes in husksand destruction of the cobs.Frass can be a contaminationissue, even if caterpillars areremoved. Heliothis is the mostserious pest of sweet corn.MOST COMMONWarm weather, such as fromlate spring to autumn inQueensland and summerin more southern states.Populations usually peakduring late summer.Heliothis is resistant tomany insecticides. Nuclearpolyhedrosis viruses(marketed as ViVUS)can assist control.INSECTSINSECTSHelicoverpa armigeraDAMAGELarvae feeding results indamage to silks, large raggedHeliothis egg laid singly on a corn silk (QDAF) and typical feeding damage andfrass in the leaf whorlCaterpillars attacking the tassels and cob (A Ryland)22left: Heliothis caterpillar killed by the biopesticide Vivus (a virus); right: Heliothismoths often hide in the leaf whorl during the day23

Hoverfly Lacewing — brown and green BeneficialDESCRIPTIONMOST COMMONDESCRIPTIONLarvae: Cream to brownishmaggot with stripe on uppersurface and dark mouthhooks, up to 10 mm long.Warm weather,especially summer.Nymph: Brown lacewingnymphs are slender, brownand up to 10 mm longwith a smallish head butlarge jaws and a long tail.Green lacewing nymphsare thicker bodied, up to8 mm long and usuallycamouflage themselves withthe remains of their prey.Adult: Resembles a bee orwasp with black and yellowbands across its ratherflattened abdomen, butactually harmless. Oftenhovers near flowers, feedingon nectar and pollen.BENEFITLarvae eat largenumbers of aphids.insectMicromus tasmaniae Adult: Brown lacewings areup to 8 mm long with largegreen eyes. Green lacewingsare up to 15 mm long withlarge round red eyes and longantennae. Both have large,delicately-veined wings heldupright along the body.INSECTSINSECTSSyrphidae spp.BeneficialinsectBENEFITAdults and nymphs arevoracious predators ofaphids, small caterpillars,thrips and mites.MOST COMMONYear round.Hoverfly larvae attacking aphids (P Scanlon DAFWA) and adult24Clockwise from above: Brown lacewing nymph attacking aphids (C Freebairn QDAF);Brown and green adult lacewings; Green lacewing nymph (S Broughton DAFWA)25

LadybirdDESCRIPTIONMOST COMMONNymph: Black with colouredmarkings and ‘crocodile like’appearance, up to 6 mm long.Late spring to autumn. INSECTSINSECTSCoccinella transversa, Hippodamia variegate, Harmonia conformisBeneficialinsectAdult: Most are brightlycoloured, dome-shapedbeetles 3–5 mm long withdistinctive spots and stripeson their outer wing covers. Incontrast, Stethorus is black,hairy and 1–2 mm long.BENEFIT26Both adults and larvae areactive predators of aphids,thrips, moth eggs and mites.White collared ladybird (H. variegate) adult and nymph (opposite)Transverse ladybird (C. transversa) adultCommon spotted ladybird (H. conformis) and mite eating ladybird (Stethorus)with two spotted mites (QDAF)27

INSECTSMaize thripsCicadulina bimaculataFrankliniella williamsiDESCRIPTIONDESCRIPTIONNymph: Similar to adult butsmaller, paler and wingless.ear’. Symptoms includeseverely stunted growthAdult: Wedge-shaped golden and swelling of the leafyellow insect with clear wings, veins. Leaves tend to crinkleand in-roll, developing adark eyes and black spotseither side of the ‘nose’. Looks shortened, upright habit.like a tiny (3 mm long) cicada. MOST COMMONThey quickly jump away inLate summer, particularlyany direction if disturbed.in coastal areas. SomeDAMAGEvarieties are more susceptibleto damage than others.Maize leafhoppers inject aPlants can recover fromtoxin into the leaf duringwallaby ear symptoms iffeeding. This toxin causes asyndrome known as ‘wallaby leafhoppers are controlled.Nymph: Cream toyellowish, wingless,generally 1 mm long.Maize leafhoppers on a leaf (QDAF) and in close-up (H Lockyer NSW DPI);Symptoms of ‘wallaby ear’ due to leafhopper damageFeeding damage on sweet corn leaves. A single thrips is just visible in theclose-up (J Duff QDAF)Adult: Light to dark brown,torpedo-shaped and 1–2 mmlong. Narrow transparentwings fringed with long hairsare held along their backs.growth, feeding on the cobcreates an entry point fordiseases such as Fusarium.INSECTS28Maize leafhopper (Wallaby ear)MOST COMMONWarm to hot, dry weather.DAMAGEFeeding in the leaf whorl cancause the leaves to becomedistorted and cupped, withyellow streaks developing.While this does not appearto significantly affect plant29

Mite — predatory Mite — two-spottedTetranychus urticaeDESCRIPTIONBENEFITDESCRIPTIONP. persimilis can be purchasedcommercially. Various otherpredatory mites can also befound in unsprayed crops.Predatory on twospotted mite.Nymph: Translucent white,changing to bright orangein overwintering form.Nymph: Pale orange,pear shaped.MOST COMMONMultiplies rapidly attemperatures 26 C.Adult: Orange to reddish,pear shaped. Faster movingand larger than pest mites.the yellowed area spreadsand may turn reddish.Leaf undersides becomecovered in fine webbing.INSECTSINSECTSPhytoseiulus persimilisBeneficialinsectAdult: Whitish to yellowgreen, around 0.5 mmMOST COMMONlong with a dark olive spotHot (25–30 C) dry weather.either side of its body.Overwintering form has a darkred body and white legs.DAMAGEFeeding damages leaves,which initially developlight yellow stippled areas.As populations increasePredatory mite Phytoseiulis persimilis attacking a two spotted mite (QDAF)30Two-spotted spider mites (F Peairs CSU Bugwood.org) and leaf damage with close-up31

INSECTSTrichogramma spp. Telenomus spp. Microplitis spp. Cotesia spp.DESCRIPTIONThere are many differenttypes of parasitoid wasp,of which a number are soldcommercially for control ofcaterpillars and aphids.Adult: Egg parasitoidssuch as Trichogramma,Telenomus and Trissolcusbasalis are tiny black orbrown wasps 0.5 mmlong. Larval parasitoids arelarger, 3 to 20 mm long.while T. basalis attacksgreen vegetable bug eggs.Microplitis lays a single egginto heliothis and Spodopteraspp. caterpillars. Braconidwasps such as Cotesiaspp. parasitise heliothis,armyworm and sorghumhead caterpillars, with up to30 mature larvae formingfluffy white pupae on theoutside of the dead host.BENEFITMOST COMMONINSECTSBeneficialinsectParasitoid waspsMicroplitis spp. (JK Lindsey)Trichogramma and Telenomus Any time of year.parasitise heliothis eggsTelenomus spp. (B Scholz QDAF) and Trichogramma spp. (NSW DPI) laying intoheliothis eggs32Parasitoid wasp newly emerged from its mummified aphid host (J Duff QDAF);Cotesia wasp pupae (J Duff QDAF)33

INSECTSOrius spp.DESCRIPTIONBENEFITFeeds on thrips, mites andNymph: Bright orange-red,wingless nymph with dark red a variety of moth eggseyes and plump appearance. including heliothis.Adult: Oval bug 2–3 mmlong with clear wingsfolded flat across its back.Prominent piercing andsucking mouthpart.MOST COMMONIn summer.Plague soldier beetleChauliognathus lugubrisDESCRIPTIONLarvae: Soil dwelling grub.A strict carnivore thateats insect pupae, eggsand young caterpillars.INSECTSBeneficialinsectPirate bugAdult: Slender beetle withbright orange abdomenand metallic green wings.Up to 15 mm long.BENEFIT / DAMAGEPredatory on aphids,caterpillar eggs and otherpests. However large numbersmay cause crop damageand contaminate cobs.Pirate bug nymph (A Sisson Iowa State Uni Bugwood.org), adult (P Scanlon DAFWA)and pirate bug hunting on corn silks, showing its small size34Plague soldier beetle singly and swarming on corn tassels (A Ryland)35

Planthopper36DESCRIPTIONDicranolaius bellulusBeneficialinsect DESCRIPTIONMOST COMMONthey suck plant sap andexcrete honeydew. Thisreduces plant vigour, resultingin leaf yellowing, wilting andAdult: Mottled brown withlighter patch on the top of the withering. Young seedlingshead. Resemble tiny cicadas. may be killed. Growth of sootymould on honeydew reducesAdults may be short- orphotosynthesis. Planthopperslong-winged, with the lattercan transmit viruses,being around 4 mm long.particularly maize stripe virus.DAMAGEMOST COMMONAdults and nymphs canWarm,humid weather.gather in large numbersinside the leaf whorl, whereLarvae: Creamy, soildwelling grub.In summer. Active mainlyin the early morningand at sunset.Maize planthopper (Peregrinus maidis) (USDA ARS); Planthopper adult,species undeterminedFemale red and blue beetle hunting aphids (top) and male beetle showingdistinctive antennae ‘clubs’Nymph: Creamycoloured, oval nymphwith short wing stubs.Adult: Glossy beetle around5 mm long with blue head andorange thorax. The metallicblue wing covers have adistinctive broad orangeband across the centre andan orange tip at the end.INSECTSINSECTSFamily DelphacidaeRed and blue beetleBENEFITFeeds on heliothis eggs andsmall caterpillars. Adultsalso sometimes eat pollen.37

Red-shouldered leaf beetleNysius vinitorDESCRIPTIONMOST COMMONDESCRIPTIONLarvae: White grub withbrown plates at the headand tail, up to 10 mm long.Swarms appear from springto autumn, particularly incoastal areas of northernNSW and Queensland.Nymph: Pear-shaped, reddishbrown and wingless. Nymphsmainly feed on weeds.Adult: Golden yellow beetlearound 6 mm long withdark red band across theshoulders and a dark redspot on each wing cover.DAMAGEAdults eat leaves. Larvae feedon plant roots but are notgenerally a problem in corn.Only occasionally a pest butcan cause severe damage ifpresent in large numbers.Adult beetle (P Chew); Red-shouldered leaf beetle feeding on the leaf (QDAF)38Rutherglen bugINSECTSINSECTSMonolepta australisAdult: Slender, dark grey bugs5mm long with transparentwings and large black eyes.DAMAGESap sucking can dry outtassels and silks as well asdamage leaves and husks.Can contaminate packed cobs.MOST COMMONMultiplies during spring andearly summer in weed species.Usually moves into corn whenother hosts are unavailable.Rutherglen bug adult on a cob, in large numbers sucking sap from the tassel,and the resulting dried out tassels (A Ryland)39

Sorghum head caterpillarScutigerella spp.DESCRIPTIONDESCRIPTIONMOST COMMONCaterpillar: Young larvaeare beige but darken withage to brown or grey withdarker stripes. Resemblearmyworm but are smaller(up to 13 mm long) and lackthe distinguishing three whitestripes behind the head.Juveniles and adults look liketiny (3–7 mm long), white,soft-bodied centipedes.The number of pairs of legsincreases each time theanimal moults, reaching amaximum of twelve pairs.If disturbed, symphilidsmove rapidly throughpores and gaps in the soilto escape the light.Well structured, moist soils,particularly if temperaturesare mild. Symphyla move upor down the soil profile inresponse to moisture levels,so are less likely to attackseeds in dry conditions.Both larvae and their frass canbe a contamination issue.MOST COMMONAn occasional pest in NSW,Queensland and the NT.Mainly attacks sorghum.Adult: Slender mottled greyand reddish-brown mothup to 8 mm long. Wings arefolded along the body.DAMAGECaterpillars feed on silks andwrapper leaves of cobs.Young sorghum head caterpillar with damage, and the caterpillar and mothclose up (QDAF)40SymphylaINSECTSINSECTSCryptoblabes adocetaDAMAGEWhile symphyla normally eatdecaying vegetation, theywill also attack germinatingseeds, roots and root hairs.Heavy infestations can causemajor losses of germinatingseeds and seedlings.Symphyla in close up (S Martinez) and with a damaged seed showing size(M Hinderager)41

INSECTSNaupactus leucolomaDESCRIPTIONBENEFITDESCRIPTIONEgg: Creamy oval egg, laidsingly or in a small group,usually stuck directly ontothe skin of a host caterpillar.Larvae feed insidecaterpillars such as heliothis.Although they do not killthe host immediately, itdies during pupation.Larvae: Whitish C-shapedlegless grub with creamyhead and black jaws,up to 15 mm long.Larvae: White, carrotshaped maggot thatlives inside the host.MOST COMMONAny time of year.Adult: Tachinid flies havea very large size range.Most are grey or brown,similar to a housefly, butstrongly bristled and oftenwith a stout appearance.Tachinid fly (P Chew) and attacking a heliothis caterpillar (QDAF)42White fringed weevilAdult: Pale grey-brownstriped weevil with whiteside band and short broadsnout. Up to 12 mm long.Adults cannot fly but canwalk long distances.DAMAGELarvae live in the soil wherethey eat plant roots. Theycan kill young seedlings bychewing through the stembelow the soil surface. Adultsrarely cause major damage.INSECTSBeneficialinsectTachinid fliesMOST COMMONMainly a pest of legumessuch as peas and lucerne,but will attack cornespecially if it is grownafter a more susceptiblecrop. Larvae are active fromautumn to spring, adultsemerge during summer.White fringed weevil larvae (S Andreoli BGA AgriServices) and adult43

Wireworms — False and trueDESCRIPTIONDAMAGELarvae: False wirewormlarvae are smooth, goldento brown and up to 30 mmlong with a round headand dark mouthparts.True wireworm larvae arecreamy to light brown witha darker, reddish head andtail. They are softer bodiedthan false wireworms andthe tail is usually forkedwith a serrated edge.Larvae live in the soil wherethey feed on germinatingseeds, young plant rootsand stem bases.Adult: False wirewormsmature into ‘darkling’ beetles.These dark, oval-shapedbeetles have a thorax withflanged edges (like a pie dish).True wireworms becometorpedo-shaped ‘click beetles’,so called because they canright themselves with a clickif placed upside down.False (Virginia Tech Extension) and true (GRDC) wireworm larvae44INSECTSINSECTSGonocephalum spp., Family ElateridaeMOST COMMONMost likely to be a problemwhen corn is planted ina field formerly plantedwith pasture or mulches.Darkling beetle (adult false wireworm) (U Schmidt) and click beetle (adult truewireworm)45

Yellow peach mothDISEASESINSECTSConogethes punctiferalisDESCRIPTIONCaterpillar: Up to 20 mmlong with a dark head. Creamyyellow to bright pink bodywith dark spots at maturity.Adult: Bright orangeyellow moth with spottedblack markings. Wingsheld out from body.DAMAGECaterpillars feed ondeveloping cobs.MOST COMMONDecember to May.DiseasesYoung yellow peach moth caterpillar, caterpillar with feeding damage in corn(QDAF) and adult moth (J Tann)4647

Brown spotUstilago maydisPhysoderma maydisSYMPTOMSThe fungus infects anyrapidly growing part of theplant, commonly the cobs,but also stems, tassels andleaves. Pale green to greygalls form and enlarge,reaching up to 150 mmdiameter on the cobs. Theseeventually burst, releasingmasses of dark spores.SYMPTOMSwhile resting spores oncrop residues are known topotentially survive in thesoil for more than 15 years.FAVOURED BYWarm (23–30 C) andhumid weather. Infectionrequires free water, so ismore likely after

African black beetle 3 Aphid — corn 4 Aphid — green peach 5 Armyworm 6 Assassin bug 8 Big eyed bug 9 Black headed mirid 10 Brown marmorated stink bug 11 Cluster caterpillar 12 Cricket — black field 13 Cricket — mole 14 Cutworm 15 Damsel