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FIELD PESTS | STORED GRAIN PESTS
WESTERN
SECTION 7INSECT CONTROL
OATS
FEBRUARY 2016
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SECTION 7
Insect control
Damagefromfieldinsectsisnotgenerallyamajorfactorforoatcrops.Mitescanbeathreatwhenoatsareattheseedlingstage,andaphidsareabletotransmitviruses.Damagefromotherpestscanoccurifpopulationsbuildup.Graininsectsarenotpermittedinexportgrainorgrainforsale,andthereisazerotoleranceforinsectsinexporthay.Protectingagainstfieldandstoredgrainpestsisthereforecritical.1
7.1 Field pestsPlanningrotationstominimisepestcarryover,timelysowing,adequatecropnutritionandgoodcontrolofweedandrootdiseaseswillallassistinreducingthelikelihoodofcrop attack by insect pests.
Checkcropsregularlythroughouttheirgrowthforfieldinsects.Controlredleggedearthmiteandlucernefleaduringtheseedlingstageifnecessary.Checkforandcontrolaphidsfromtheflag-leafstage,andlaterincropsconsideredhighyielding.Aphidscantransmit Barley yellow dwarf virus(BYDV).IfgrowingsusceptiblevarietiesinareaswithmoderatetohighriskofBYDV,thensprayingthecropwithasyntheticpyrethroidat~30daysaftersowingisadvisable.
Correctidentificationoftheinsectiscriticalforsuccessfulmanagement.2
7.1.1 CockchaferCrop stageLookforcockchafersbeforeseeding.
DescriptionThereareseveralimportantpestspecies,andadultsrangeinsizefrom5to20mm.Adultsareusuallybrownorblackishbeetles.Thebeetlesflyreadilyandareattractedtolights.CockchaferlarvaearecharacteristicallyC-shaped,creamywhitegrubs2–25mmlong (Figure 1).
Life cycleSome species have a long larval stage that extends over 12–18 months. In most species,larvaeareactiveduringlateautumnandwinter.Inthesespecies,pupationoccursinspringandadultsemergeinearlysummer.Feeding,matingandegg-layingmay occur throughout summer.
DamageCockchaferlarvaefeedundergroundandsomespeciesareseriouspeststhatmaycausepatchesandpoorgrowthinpastureandmayslowgrowthorkilllargeareasofcerealsandlupins.Youngplantswithoutextensiverootsystemsareworstaffected.Theadultbeetlesarealsoverydestructivebecausetheyfeedontreefoliage.
1 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
2 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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ControlControlofcockchaferlarvaeisrarelywarranted.ThepestspeciesinWesternAustraliacannotbecontrolledwithchemicalsafterplantingbecausethelarvaeremainunderground.Cultivation,shallowplantingandahighseedingratemayhelptoovercometheproblem,whichismostseriouswhenearlygrowthisslow.Largepopulations may be present under young crops and in pasture without causing significantdamage.3
Figure 1: Cockchafer larvae (left panel) and adults (right panels). (Photos: DAFWA)
3 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.2 Desiantha weevilCrop stageLookforDesianthaweevillarvaebeforeseedingandatseedlingstage.
DescriptionThelarvaearewhite,leglesscreatures6mmlongandwithorange-brownheads.Theyremainunderthesoilandaredifficulttolocate,althoughsomepainstakingdiggingmayreveal the larvae close to plants. The adults are grey-black weevils approximately 5 mm long with the typical weevil snout (Figure 2).
Life cycleEggsarelaidinautumnandhatchafteropeningrain,andthelarvaecommencefeedingonyoungpastureseedlings.Whencerealcropsareplantedintoheavilyinfestedpaddocks,theyareattackedbythelarvae,whichmaybewellgrown.Inspring,thelarvaepupateandbecomeadults.Adultsarecommoninspringandsummer,hidingunderwoodorstones;theycanbefoundoncerealheads,wheretheycanbeharvestedwith the grain.
DamageDesianthaweevilisasporadicpestofcerealseedlingsinsoutherncoastalareas.Thelarvalstagecandestroyhundredsofhectaresormayaffectsmallerareasbyfeedingonundergroundpartsoftheseedlings.Plantgrowthmaybeslowedorplantsmaywiltanddie,inwhichcasetheymaybeeasilypulledfromthesoil.
ControlControlwithchemicalsisnotpossibleafterplanting.Theproblemismostlikelywhereshallowsandoccursovergravelorclay.Larvaewillbelargerfollowingsummerrain,so crops should be planted early and shallow to minimise attack. Where the pest is confirmed,plantingwithtreatedseedat90kg/haisrecommended.4
Figure 2: Desiantha weevil (Desiantha diversipes) larva (left) and adults (middle and right). (Photos: DAFWA)
4 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.3 CutwormCrop stageLookforcutwormsbeforeseedingandatseedlingstage.
DescriptionSeveral species (Agrotis infusa,A. munda,variousotherspecies)occurinWesternAustralia,andtheyvaryinappearance,butthelarvaeareallsmoothandplump(Figure3).Larvaeofthemostcommonspecies,thepinkcutworm,aregrey-greenwithapinktingeandareusuallyfoundinsandysoils.Larvaeofanothercommonspecies,theBogongmoth,aredarkgrey.Larvaeusuallyhidebydaybuttheymaybefoundunderthesurfaceandoftenclosetoadamagedplant.Theycurlupwhendisturbed.Attimes,browncutwormswithaherringbonepatternalongthebackdamagecrops.Insoutherncoastalareas,theyaremorelikelythanpinkorblackcutwormstobefoundonthesoilsurfacebyday.Theadultsoftheseherringbonecutwormsareofvariousspecies,andcanrangefromblack,throughgreytobrown.Occasionally,autumnattackbyarmywormincerealsresemblescutwormdamage.Thisissignificant,becausearmyworms are harder to kill with insecticides than are cutworm.
Life cycleEggs are laid on the soil or on plant material close to the ground. The larvae may grow 50mmlongbeforepupatingandthenfinallybecomingadultmoths.Adultsarestout-bodied,withawingspanofupto40mm.Theforewingsarepatternedbrownordarkgrey. Several generations are possible in one season.
DamageAsthenameimplies,thecutwormchewsthroughplantparts,oftenfellingtheplantatgroundlevel.Justtwoorthreelargecaterpillarswouldseriouslydamageasquaremetreofcrop,andalmostallcropandpastureplantsaresusceptibletoattack.Thisisnotaregularpestbutlargeareasmaybeaffected.
ControlWeatherandfoodsupplyarethemostimportantfactorsdeterminingabundance.Biologicalcontrol,suchasbyfungaldiseases,maybeverysuccessful.Waspandflyparasitesarealsoveryactiveinpreventingmorefrequentandseriousoutbreaks.5
Figure 3: Cutworm larvae (left panel) and moths (right panel). (Photo: DAFWA)
5 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.4 WebwormCrop stageWebwormsarepresentbeforeseedingandatseedlingstage.
DescriptionWebwormcaterpillarsareseldomseen,beingabovegroundlevelonlywhenconditionsarecoolanddampandusuallyatnight.Theymaybeintheirweb-linedtunnels,fromwhich plant parts may be seen protruding. The caterpillars are pale to deep brown with atingeofthegreengutcontentsshowingthrough.Theheadappearsblackordarkbrown(Figure4).Fullygrowncaterpillarsare~15mmlong.
Life cycleCaterpillarshatchfromeggslaidamongstgrassinautumnandtheyfeedthroughoutwinter.Springandsummerarepassedinthetunnelsasresting-stagecaterpillars.Afterthis,theinsectsproceedthroughthepupalstageandemergeasadultmoths,whichareabout10mmlongandmaybeseenflyinginlargenumbersonautumnnights.Byday,theyhideincamouflageindrygrass.
DamageThecontinualchewingdamageofaheavywebworminfestationmaydestroylargeareasofemergingwheatorbarleycrops.Thecaterpillarsseverleavesorwholeplants,whichtheyscatteronthegroundorpullintoholesneartheplants.Inpasture,thegrasscomponentmayberemovedfromlargeareas.
ControlThe paddock condition in autumn and the weather are important in determining webwormnumbers.Inabarepaddockorinstubble,eggswillnotbelaidingreatnumbersandtheywillnotsurvivewell.Grassysituationsfavoursurvival.Cultivationsleadingtoaweed-freepaddockover~21daysdestroytheyoungstages,butreducedtillage cropping methods allow a greater survival. Hot and dry conditions during May andJune,resultinginalackoffeed,coulddestroymostwebworms.If~25%oftheplantsarebeingseriouslydamagedatorjustafteremergence,sprayingshouldnotbedelayed;thecontinuedfeedingwillkillmanyplantsandresultinbaregroundorthinareas. 6
Figure 4: Webworm larvae (left) and moth (right). (Photos: DAFWA)
6 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.5 Redlegged earth miteCrop stageLookformitesbeforeseedingandatseedlingstage.
DescriptionAdultmitesareaboutthesizeofapinhead(upto1mm).Theyhavevelvetyblackbodiesandeightbrightorange-redlegs.Themitesareoftengregariousandarefoundclumped together in large numbers (Figure 5). They disperse quickly when disturbed.
Life cycleMiteshatchfromover-summeringeggsduringautumnwhenadequatemoistureandsufficientlylowtemperaturesoccur.Eggsproducedthroughthegrowingseasonarethin-walledandhatchimmediately,andseveralgenerationsmaydevelopoverwinterandspring.Aspasturesbegintosenesce,themitesproducethick-walledeggs,whichresist drying over summer and carry the mite through to the next season.
DamageLargenumbersofredleggedearthmitesarecommonlyfoundinannualpasturesatthebreakoftheseason,andtheymaycauseheavylossofsubterraneancloverandannual medic seedlings. These species are susceptible throughout the growing season. Normally,mitesdonotaffectgrassesorcerealsseverely.Mitesrupturecellsonthesurfaceofleavesandfeedonexudingsap;affectedleaveslooksilvered,butdonothaveholesaswithlucernefleaattack.Mitedamagetoseedlingsismoresevereifplantgrowthisslowed.Thiscouldbecausedbycoldand/orwaterlogging,lowseedlingdensityafterafalsebreak,lowseedbanksafteracrop,orifpasturesorstubblearebeing reseeded. Cape weed increases their reproductive potential.
ControlSeedtreatmentwithasystemicinsecticidebeforesowingofpasturesorcropsprotectsseedlingsfromattack.Post-emergentspraysarealsoeffective.Usesystemicchemicalsif>60%ofplantshaveemerged.Iffewplantshavecomeupandcotyledonsaredamagedastheyemerge,itismoreeffectivetouseacontactinsecticide.Hardspringgrazing reduces damage. Biological control is being promoted through collection ofapredatorymite,theAnystismite,fromoriginalCSIROestablishmentsites,andspreadingthemthroughouttheagriculturalregion.Establishmentofthispredatordependsoncarefulhandlingduringcollectionandtransport,andonensuringareasofadequatedryplantcoverinpaddocksforshelteroversummer.7
Figure 5: Redlegged earth mites (Halotydeus destructor). (Photos: left, DAFWA; right, cesar)
7 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.6 Balaustium miteCrop stageBalaustiummitescanbefoundatseedlingstage.
DescriptionThe Balaustium mite has a greyish to red body and red legs and is similar in appearance totheredleggedearthmite.Ifviewedunderamagnifyingglassormicroscope,shortstout hairs can be seen covering the body (Figure 6). The adult grows to almost twice thesizeofredleggedearthmites.
Life cycleBalaustiummitesrequirerainfallbeforeover-summeringeggscanhatch.Newlyhatchednymphshavesixlegsandareorange.Developmentfromeggtoadulttakesabout5–6weeks. Several generations can occur each year.
DamageAlthough Balaustiummitesareseeninpasturesandoccasionallyincrops,itwasnotuntil1997thatreportswerereceivedofthembeinganeconomicpest.SomepropertieswestofRaventhorpeandsomeintheEsperanceareahavehadcereal,lupinandcanolacropsseverelybleachedandwiltedtothepointofdeathfromthispest.Mitesfeedontheleavesofplantsbyprobingintothesurfacecellswiththeirmouthpartsandsuckingout sap. Reports indicate that crops sown into paddocks that were in pasture the previousyear,withhighlevelsofbroadleafweeds(especiallycapeweed),willbemostatriskfrommitedamage.
ControlInmostsituations,cropswillnotrequiresprayingandthemiteswillcauselittleornodamage.Earlycontrolofsummerweedsinpaddocksthataretobecroppedwillpreventbuildupofmitepopulations.WeedspresentinpaddockspriortocroppingshouldbecheckedtodeterminethenumbersofBalaustiummitespresent.Ifthereareverylargenumbers,incorporationofinsecticidewithherbicideimmediatelypriortosowingisamoreeffectivestrategythansprayingwhenthecropisemergingandhasverylittlecoverofgreenmaterial.NochemicalsarecurrentlyregisteredforcontrolofBalaustiummite.Farmertrialshaveshownhighratesofsyntheticpyrethroidscanbeeffective;however,themitescanbedifficulttokill.Highratesofdimethoate,omethoate,chlorpyrifosandphosmethavebeenfoundineffectiveincontrollingthesemites.8
Figure 6: Balaustium mite (Balaustium medicagoense). (Photo: cesar)
8 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.7 Bryobia miteCrop stageBryobia mites are present at seedling stage.
DescriptionThe adult mites are slightly smaller than a pinhead with a dark grey body and pale red–orangelegs.Theycanbeconfusedwithredleggedearthmiteandaredifficulttoseparatewithouttheuseofahandlens.However,redleggedearthmitesarenotusuallypresentuntillaterinautumnbecausetheyhaveacoldtemperaturerequirementbeforehatching.ThefrontlegsonBryobiamitesareverylongandheldinfrontofthebodylikeapairoffeelers(Figure7).Thebodyisroundedandplump,butifthemiteisstarved,itsbodyshapechangestoflatonthetopandroundedunderneathwithaflangearoundthe sides.
Life cycleAdult Bryobiamitesareactiveinlatespring,summerandautumn.Eggsarepresentoverwinter,andtheyhatchasconditionsdryandwarmupinspringandearlysummer.Wintereggsareusuallylaidinbatches,whereaseggsoverthedryperiodarelaidsinglyonbacksofleavesofhostplants.Nymphsnewlyhatchedhavesixlegsandarebrightred,butturndark-greyinafewdays.Theymoulttoanymphwitheightlegs,thenagaintobecomeathird-stagenymph,beforefinallymoultingtotheadultstage.Onemonthfromegghatchingtoyoungadultisusual.Thereareseveralgenerationsperyear.
DamageWheninhighnumbers,Bryobia mites have caused severe damage to emerging canola andlupincropsinautumn.Mitesfeedonthetopsofleavesbystabbingintothesurfacecellswiththeirsharpmouthparts,andsuckingoutsap.Whitishgreyspotsresult,givingleavesastippledwiltedlook.Summerrainsfollowedbywarmmildautumnsgive Bryobiamitesthebestconditionsforsurvivalandincrease.TheydonottoleratecoldwetweatherbutcanpersistintoJunefollowingwarmautumnconditions.Cropsplantedintopaddockswithahistoryofsummer–earlyautumnweeds,andexperiencingwarmdryconditionsaftercropemergence,aremostatrisk.Reportsofdamagehaveincreasedsince1995,beforewhichBryobia mites were considered a minor and sporadicpestinsomesoutherndistrictsofWesternAustralia.Theywerereportedasbeing a serious pest in central and some northern cropping zones during autumn 1998 and1999.Minimumtillage,earliersowingtimesandtolerancetosomeinsecticideshaveledtotheincreasedimportanceofthispest.
ControlEarlycontrolofsummerweedsinpaddocksthataretobecroppedwillpreventthebuildupofmitepopulations. Weeds present in paddocks prior to cropping should be checked to determine the numbersofmitespresent.Iftheyarefoundinlargenumbers,thenincorporationofinsecticidewith herbicide immediately prior to sowing is moreeffectivethansprayingwhenthecropisemergingandhasverylittlecoverofgreenmaterial.OmethoateisregisteredforcontrolofBryobia mite in pastures and some crops. RatesofinsecticidescommonlyusedtocontrolredleggedearthmiteandlucernefleaarenoteffectiveagainstBryobia mites. 9
9 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
Figure 7: Bryobia mite. (Photo: DAFWA)
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7.1.8 Blue oat mite BlueoatmitesareoftenconfusedwithRLEM.Therearefourrecognisedspeciesofblue oat mite in Australia: Penthaleus major,P. falcatus,P. minor and P. tectus. Accurate identificationofthespeciesrequiresexaminationbyanentomologist.Thefourspeciesvary in their geographical distribution in Australia.
Damage to crops and pastures is incurred in the establishment phase. Host-plant preferencesvarywiththespecies,asdotheirlifecyclesandtolerancestovariouspesticides.Hostplantsincludeblackthistle,chickweed,curleddock,dandelion,deadnettle,pricklylettuce,shepherdspurse,variegatedthistleandwildoat.Cultivatedfield-crophostsincludewheat,barley,oats,rye,canola,fieldpeas,lupinsandlinseed.
Description Adultmiteshaveeightlegsandare~1mmlongwithoval,rounded,darkbrowntoblackbodies,brightredorpinkishredlegsandmouthparts,andaredspotorstreaktowardsthehindendoftheback.
Seasonal development Overlappinggenerationsoftheblueoatmiteusuallyoccurbetweenmid-autumnandlate spring. Blue oat mites oversummer as aestivating eggs laid in mid–late spring by the second-generation adults. These aestivating eggs are highly resistant to desiccation. They do not begin to develop until late summer–early autumn and they do nothatchuntilfavourableconditionsoftemperatureandmoistureoccurinthefollowingmid-autumn to early winter. 10
7.1.9 Lucerne fleaCrop stageLookforlucernefleasatseedlingstage.
DescriptionLucernefleasusuallyspringfromtheplantswhenapproached,usingaspecialisedorganunderneaththebody.Thelucernefleaisadumpylookingandwinglesscreatureofvariedcolour,butthelargerspecimensof2–4mmarepredominantlygreenoryellow(Figure 8).
Life cycleThefirstsoakingautumnrainscausetheover-summeringeggbatchestohatch.Severalgenerations may then develop over the growing period depending on the weather. Eggs arelaidinthesoilandtheyusuallyhatchinafewdays.Withtheonsetofwarmanddryconditionsinspring,theresting-stageeggs,whichareabletowithstandsummerconditions,arelaid.
DamagePastures,legumecropsandcerealsmaybeseriouslyretardedbythelucerneflea,andseedlingdeathmayoccurduringheavyinfestations.Frequently,thegreenleaftissuesareeaten,leavingasurfaceoftheleafasawhitishfilm.Fromadistance,severelyaffectedareasappearbleached.
ControlThelucernefleaisfavouredbyheavysoilsandcannotliveinverysandysituations.Itisalsodependentonplentifulmoisture.Controlincropsandpasturesmaybeobtainedwithsystemicorcontactinsecticides,asforredleggedearthmites.Apredatorymite,the Bdellodesmite,ispresentovermostoftheareaoccupiedbylucernefleaandexerts
10 KHertel,KRoberts,PBowden(2013)Insectandmitecontrolinfieldcrops.NSWDPIManagementGuide.NSWDepartmentofPrimaryIndustries,http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0005/284576/Insect-and-mite-control-in-field-crops-2013.pdf
i More information
DAFWA: Diagnosing blue oat mite
Crop mites. Back Pocket Guide
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ausefullevelofcontrol.Anotherpredatorymite,theNeomolgusmite,wasintroducedby the CSIRO and it has been released throughout the agricultural area. It will extend therangeandlevelofbiologicalcontrol.11
Figure 8: Lucerne flea (Sminthurus viridis). (Photo: DAFWA)
7.1.10 Cereal aphidsCrop stageAphidsaredamagingattilleringandfromfloweringtomaturity,andtheytransmitBYDV.
DescriptionThe corn aphid (Rhopalosiphum maidis) and wheat or oat aphid (R. padi) cause the greatestyieldloss(Figure9).Winglessfemalesareabout0.2–2.5mmlong.Rice-rootaphid (R. rufiabdominalis) and grain aphid (Sitobion miscanthi)arealsofoundincerealsand may be important as virus vectors.
Cornaphidsaredarkblue-greentogrey-green,oftenwithafinewhitepowderydustoverthebody.Coloniesdevelopwithinthefurledtipoftillers,startinganytimefromseedlingstagetoheademergence.Fewfarmersseethembecausetheyarehiddeninthefurledleaves.Cornaphidprobablykillstillers,resultinginfewerheads.
Wheatoroataphidsvaryfrommottledyellow-greenthrougholivegreenandduskybrown,toablackishgreen.Coloniesdevelopontheoutsideoftillersfromthebaseupwards,onstems,nodesandbacksofmatureleaves,startinganytimebetweenlatetilleringandgrainfilling.Heavyinfestationscanblackenheadsandflagleaves,andthesearetheaphidsmostcommonlyreportedbyfarmers.Wheatoroataphidsaremoremobilethancornaphids,and can drop to the soil and crawl to other plants. They cause yield losses probably by reducing grain weight and grains per head. They may also be important in spreading BYDV.
Ricerootaphidsaresimilartowheatoroataphids,buttheycanalsoinfestplantroots.Theyhaveareddishpatchinthemiddleoftheback,andaremostlikelytobefoundindrieragriculturalareas.Grain aphids are dusky green with yellow-green tinges,usuallyfoundinspring,withoutdevelopinglarge colonies. Rose-grain aphids are potentially seriouspests,buthavenotyetreachedWestern
11 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
Figure 9: Oat or wheat aphid (Rhopalosiphum padi) and corn aphid (R. maidis). (Photos: DAF Qld)
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Australiafromtheeasternstateswheretheyarewidespread.Theyaregreenspindle-shapedaphidsattackingwheatandbarleyduringgrainfilling.
Life cycleWingedaphidsflyintocropsfrompasturegrassesorothercropsandstartcoloniesofwinglessaphids.Reproductionisrapidwhenweatherconditionsarefavourable,leading to population outbreaks. Plants can become sticky with honeydew excreted by theaphids.Whenplantsbecomeunsuitableorovercrowdingoccurs,wingedaphidsredevelop and migrate to other plants or crops. They can carry viruses in saliva or on theirfeedingtubes.BYDVdamageismostseriousafterplantinfectionearlyintheseason.
DamageCerealaphiddamageinoats,barleyandwheathasnoobvioussignsorsymptoms.Researchinmedium-andhigh-rainfallzoneshasshownthataphidscancauselossesupto30%wherecropyieldpotentialis≥3t/ha.Damagingpopulationsmaydevelopin60%ofyears.Aphidsaffectcerealsbydirectfeedingonplants,and/orbytransmittingBYDV,whichaffectswheat,oatsandbarley.Directdamageoccurswhencoloniesof10–100aphidsdeveloponstems,leavesandheadsfromseedlingstagethroughtoheadfilling.Thedegreeofdamagedependsonthepercentageoftillersinfested,numberofaphidspertiller,andthedurationoftheinfestation.
ControlInsouthernareas,cropsshouldbecheckedfromlatetilleringonwardsforcornaphidsinthefurledgrowingtips,andforwheatoroataphidsonstems,backsofleavesandinthecrown.Highyieldingcropsaremostatrisk.Sprayingisworthwhileif50%oftillershave>10aphids.Mixedinfestationsofbothaphidspeciesmaycausemoredamagethaneitherspeciesontheirown.CropssprayedbeforeZadoksgrowthstage(GS)30mayneedresprayingatGS50orlaterifaphidnumbersbuildupagain.Parasiticwasps,ladybeetles,lacewingsandhoverfliescanprovideusefulbiologicalcontrol,mainlybypreventingsecondaryoutbreaks.Useof‘soft’insecticidesthatkillonlyaphidsisadvocated. 12
Thresholds for controlInspectforaphidsthroughoutthegrowingseasonbymonitoringleaves,stemsandheadsaswellasexposedroots.Choosesix,widelyspacedpositionsinthecrop,andateachpositionexaminefiveconsecutiveplantsinarow.Researchisunderwayintodamagethresholdsandcontroloptionsforcerealaphids.
Thedecisiontocontrolaphidsonwintercerealsdependsonthesizeoftheaphidpopulationandthedurationandtimingoftheinfestation.Controllingaphidsduringearlycropdevelopmentgenerallyresultsinarecoveryoftherateofrootandshootdevelopment,buttherecanbeadelay.Aphidsaremorereadilycontrolledinseedlingandpre-tilleringcrops,whicharelessbulkythanpost-tilleringcrops.Cornaphidsintheterminalleaftendtodisappearascropscomeintohead,andotherspeciesusuallydecline in abundance about this time as natural enemy populations build up. Note that becausethericerootaphidfeedsbelowground,itcannotbecontrolledeffectivelybynon-systemicfoliartreatments.13
Nofirmeconomicthresholdsexist(takingintoaccountcurrentcostsofcontrolandcropvalue),buttherearethresholdssuggestedfromresearchinWesternAustraliaandbytheNorthernGrowerAlliance.TheWesternAustralianthreshold,basedoncheckingcropsregularlyfromlatetillering,istoconsidercontroliftheaphidpopulationexceeds15aphids/tilleron50%oftillers.
12 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
13 DAFQld(2012)Insectpestmanagementinwintercereals.DepartmentofAgricultureandFisheriesQueensland,http://www.daff.qld.gov.au/plants/field-crops-and-pastures/broadacre-field-crops/integrated-pest-management/ipm-information-by-crop/insect-pest-management-in-winter-cereals
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7.1.11 ArmywormCrop stageArmywormsaremostdamagingfromfloweringtomaturity.
DescriptionFourspeciesofarmywormoccurinWesternAustralia:thecommonarmyworm,thesouthernarmyworm,theinlandarmywormandthesugarcanearmyworm.Ofthese,thecommon armyworm (Leucania convecta)isthemostdamaging.Mothsarestout-bodied,grey–cream,withawingspanof~40mm.Themothsflyatnightandtheyarestronglyattracted to lights.
Armyworm caterpillars vary in colour depending on their numbers in a crop. At high numbers,theybecomedark,whereasifthepopulationissmaller,thecaterpillarsaremuchpaler.Armywormsareabout40mmlongwhenfullygrownandcanbedistinguishedfromcutwormsandbudwormsbytheirlargeheadsandbythreeprominentwhitestripesonthe‘collar’behindthehead(Figure10).Oftentheywillnotbeseenbecausetheyfeedmainlyatnight;however,theirdroppings,whichlooklikesmallgreen‘square’haybales,willbeobviousonthegroundbelowthecropcanopy.Anotherindicator that armyworms are present is damage to ryegrass seed heads.
Life cycleArmywormshavethreeorfourgenerationseachyear,andonthesouthcoasttheysurviveoversummeronself-sowncerealsandgrassesthatgerminatewithsummerrains.Inspring,itisabout21daysfromwheneggsarelaidtowhenthecaterpillarsreachhead-loppingsize.Oncedamagebegins,manyheadscanbeloppedinashorttime.
DamageArmywormsareregularpestsofcoarsegraincropsonthesouthcoastofWesternAustraliaandoccasionalpestsininlandareas.Towardstheendofspring,whencropsareapproachingmaturity,largecaterpillarschewthroughthestemjustbelowthehead,causingtheheadtofalltotheground.Ifinlargenumbersearlierintheseason,theymayeatleavesandtheymaybeconfusedwithcutworm.
ControlHeatwavesmaykillmostofthecaterpillars.Nativeparasitescanexercisegoodcontrol,and spraying is not usually required every year. Several wasp parasites including Apanteles ruficrus have been released to increase biological control. 14
Figure 10: Armyworm caterpillar. (Photo: DAF Qld)
14 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.1.12 Australian plague locustCrop stagePlaguelocustsaffectcropsfromfloweringtomaturity.
DescriptionNewlyemergednymphsareaboutthesizeofhousefliesandhopactively.Adultshaveacharacteristicblacktiptothehindwing.Swarminglocustsarelightbrown,butsolitaryindividuals may be green or yellow (Figure 11).
Life cycleTwogenerationsoccurannually.Nymphsofthefirstgenerationappearwhensoiltemperaturesbegintoriseinspring.Attainmentofadulthoodmaytake30–55daysdependingonclimaticconditions.Eggslaidbythefirstgenerationrequireatleast21daystohatchandwillhatchonlyifsufficientsoilmoistureispresent.Eggslaidbythesecondgenerationenterarestingphase,enablingthemtooverwinter.
DamageAdultlocustswilleatalmostanygreenplantmaterial,butcropsmostatriskareripeningcerealsinearlysummer,summerpasturesandgreenpasturegrowthfollowingsummerrain. Locust plagues in Western Australia are rarely as severe as the eastern states.
ControlEggparasitesarecommonbutrarelycausesignificantlosses.Severalflyparasitesarecommonandthesecondlocustgenerationisoftenheavilyparasitised.Thespeciesis declared under the Agriculture and Related Resources Protection Act and control is obligatory. 15
Figure 11: Australian plague locust (Chortoicetes terminifera). (Photo: DAFWA)
15 DAFWA(2015)Oats:insectpests.DepartmentofAgricultureandFoodWesternAustralia,https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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7.2 Stored grain pestsGraininsectsarenotpermittedinexportgrainorgrainforsale.Protectingyourgrainintendedforuseon-farmfrominsectattacksavesmoney.
• Evenlightinfestationsofweevilscanreducegerminationofthegrain.
• Weevilseatorcontaminatefoodintendedforlivestock.
• Weevilsoverwinteringinstoredgraincanre-infestmachinery.
Grainstoredon-farmwilleventuallybecomeinfestedwithgrainbeetlesormothsunlessspecificcontrolmethodsareundertaken.Goodhygieneiscritical.Otheroptionsinclude:
• cooling grain with aeration
• fumigatingasealedsilowithphosphine-generatingtablets
• applying a malathion insecticide
• treating grain by mixing with amorphous silica (e.g. Dryacide®)
Aerationwillsuppressinsectpopulationsbutnoteliminatethem.Ifdeliveringgraintoanil-tolerancemarket,farmerswilleventuallyneedtofumigate.16 See GrowNotes Oats Western,Section13,Storage.
16 DAFWA 2015 Oats: insect pests https://www.agric.wa.gov.au/oats/oats-insect-pests?page=0%2C4
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