Insect pest management in cotton.docx
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Insect pest management in cotton.docx
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Insectpestmanagementincotton
Insectpestmanagementincotton
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AdultparasitoidwaspMicroplitisdemolitor approachesacaterpillarhost.Photo:
R.Lloyd
Insectpeststhatfeedonplantstructuresthatdirectlyproduceyield,suchasgrowingtipsandfruitingstructures,aregenerallythegreatestprobleminacottoncrop.ThesepestsincludeHelicoverpaandmirids. Thecottonplanthasanindeterminategrowingpattern(fruitarepresentformostoftheseason),whichallowssomepeststodevelopthroughseveralgenerations.
Onthispage:
Geneticallymodifiedcotton
Majorpests
Helicoverpaspp.
Spidermites
Mirids
Aphids
Whiteflies
Minorpests
Thrips
Suckingbugs
Beetles
Minorcaterpillarpests
Otherpests
Geneticallymodifiedcotton
Untiltheintroductionofgeneticallymodified(GM)cotton,themaininsectpestsofcottonwerethelarvaeofHelicoverpaarmigeraandH. punctigera.Thesepestsweregenerallycontrolledwithsyntheticinsecticides,whichalsocontrolledthemajorityofothercottonpests.
Now,over90%ofthecottonareaisplantedwithvarietiesthathavebeengeneticallymodifiedtoproducehighlyspecifictoxinsthatkillHelicoverpalarvaeandmostothercaterpillarpestswhentheyfeedonthecottonplant.However,suckinginsectsmayrequiremoremanagementonBtcottoncomparedtoconventionalcotton.
ThegenesusedtoproducethetoxininGMcottonareobtainedfromanaturallyoccurringbacteriumcalled Bacillusthuringiensis (commonlyknownasBt).Insect-resistantorgeneticallymodifiedcottonisoftencalled'Btcotton'.TheintroductionofBtcottonhasresultedinasignificantreductionofinsecticideusebygrowers.
Aresistancemanagement plan(RMP)isessentialtoensurethatthesevaluable traitsremaineffective.VisittheCottonCooperativeResearchCentre(CRC)websiteformoreinformation.
Majorpests
Helicoverpa
Helicoverparemainsamajorpestonconventional(non-geneticallymodified)cotton.Thetwospecies-HelicoverpaarmigeraandH. punctigera-areverysimilarinbothappearanceandthedamagetheycausetocotton.However,correctidentificationofthespeciesisimportantbecauseH. armigerahasdevelopedhighlevelsofresistancetoinsecticides.
Speciescompositioninthecropwillbeinfluencedbythetimeofyearandlocation.Intemperateregions,themajorityoftheH. armigerapopulationoverwinterfrommid-MarchonwardsandemergeduringSeptember/October.HelicoverpapunctigeraisusuallythedominantspeciesthroughSeptember,butseasonalvariationcanleadtoearlyinfestationsofH. armigerainsomeyears,particularlyinnortherndistricts.
Helicoverpa adultsaremobileandproducelargenumbersofeggs, leadingtorapidbuild-upofpopulationsunderfavourableconditions.Survivalisinfluencedbythenumberofpredatorspresentaswellasothermortalityfactorssuchaswind,rainfallandtemperatureextremes.
Damage
Incotton,allstagesofplantgrowthmaybeattackedbutreproductivetissueispreferred.Seedlingscanbe'tippedout'whenterminalbudsareeaten.Chewingdamagetosquaresandsmallbollsmaycausethemtoshed,andchewingdamagetomaturingbolls maypreventnormaldevelopmentandcanleadtosecondaryfungalinfectionssuchasbollrot.
Monitoringandthresholds
Regularmonitoringofthecropforthepresenceoflarvaeand/ordamageisnecessaryinordertomaketimelydecisionsoncontrol.Thisisespeciallyimportantwhentargetingsmallandpossiblyinsecticide-resistantlarvae.
Visualsamplingistherecommendedmethod.Checkatleast30plantsor3separatemetresofrowforevery50 ha(largersamplesgivemoreaccurateestimates).Eggsarenot necessarilyagoodbasisforthresholdsasnotallhatchandverysmalllarvaehavehighmortalityrates.Assessbeneficialinsectnumbersandnoteparasitisedeggsandlarvae.
Whenmakingpestmanagementdecisionsincotton,insectnumbersalonemaynotbesufficient.Plantmonitoring(fruitload,yieldandmaturity)assistsindecisionmakingwhenpestlevelsarejustbelowthresholdorwhentherearecombinationsofpests.
Thresholdsforconventionalcottondependoncropstageandare:
Seedlingtoflowering:
2 larvae/mor1 larvae(>8 mm)/m.
Floweringtocut-out:
2 larvae/mor1 larvae(>8 mm)/mor5 browneggs/m.
Cut-out:
15%openbolls-3 larvae/mor1 larvae(>8 mm)/mor5 browneggs/m.
15%-40%openbolls:
5 larvae/mor2 larvae(>8 mm)/mor5 browneggs/m.
ThresholdsforBollgardII®cottonarethesamefortheentireseasonat2 larvae(>3 mm)/min2 consecutivechecksor1 larvae(>8 mm)/m.
Resistance
Helicoverpaarmigeradevelopedresistanceagainstmostinsecticidesinthelate1990s.However,withtheintroductionofgeneticallymodifiedcotton,biopesticidesandmoreselectiveinsecticides,insecticideresistancetoolderchemistryhasdecreasedinrecentyears.Helicoverpapunctigerahasnoknownresistancetoanyinsecticidesbuttheuseofmoreselectiveoptionsisencouragedtohelppreservenaturalenemies.
Inordertopreventinsecticideresistance,thecottonindustryhasdevelopedtheInsecticideResistanceManagementStrategy(IRMS).ThisstrategyisreviewedannuallytodelaydevelopmentofresistanceofH.armigeratoconventionalinsecticides.ThecoreIRMSprinciplesinclude:
rotationbetweenchemicalgroupswithdifferentmodesofaction
limitingthetimeperiodduringwhichaninsecticidecanbeused
limitingthenumberofapplicationsofoneparticularinsecticide.
VisittheCottonCooperativeResearchCentre(CRC)websiteformoreinformation.
Culturalcontrol
Post-harvestcultivation(pupaebusting)toreducetheoverwinteringstageofHelicoverpaisoneofthemostimportantculturalcontrolpracticesavailable.Cultivationtoadepthofatleast10 cmwilldamageordisturbpupae,sealtheiremergencetunnelsandtrapemergingmoths.Cultivationalsoleavessurvivorsopentoattackbybirds,mice,earwigs,andwaspparasites.
Naturalenemies
Beneficialinsects canaffectall Helicoverpalifestages:
Predators
Egg:
redandbluebeetle, damselbug, greenlacewing, brownlacewing, nightstalkingspiders,and variousants
Larvae:
glossy,brownandpredatoryshieldbugs, bigeyedbug, damselbug, assassinbug, redandbluebeetle, brownlacewing, commonbrownearwig,and spiders
Pupae:
commonbrownearwig andwirewormlarvae
Moth:
spiders
Parasitoids
Egg:
Trichogrammaspp.andTelenomusspp.
Larvae:
Microplitisdemolitor andtachinidflies
Pupae:
bandedcaterpillarparasite
Backtotop
Spidermites
The two-spottedmite(Tetranychusurticae)isthemostnumerousmitespeciesoncotton.Otherspecies thatmayoccurarebeanspidermite andstrawberryspidermite.Mitesliveontheundersideofleavesandaredifficulttargetsforaerialsprays.Mitesprefermorematureleavesandthehighestpopulationsareusuallyfoundnearthetopoftheplantonmainstemnodes3-5belowtheterminal.Heavymiteinfestationsoncottoncanoriginatefromadjoiningfieldsofearlysowncornfromwheretheyarecarriedbyaircurrents.
Damage
Miteinfestationsinseedlingcottonrarelyjustifycontrolbutmaybeausefulindicatorofpotentialproblemsandshouldbemonitoredclosely. Thefirstsignofdamageisbronzingoftheupperleafsurfacenearthepetioleorleaffold.Asnumbersincrease,the leavesturnredandbecomecoveredinfinewebbing,andaffectedleavesmaydryandfalloff.Highmitepopulationscansignificantlyaffectyieldandqualityofcotton.Theearlierintheseasonthatinfestationsdevelop,thegreaterthepotentialofyieldlossandqualitydowngrades.
Monitoringandthresholds
Startsamplingatseedlingemergenceand continueatleastweekly.Atlownumbers,mitesaredifficulttofind.Mitesareoftentoonumeroustocountindividually,soinfestationscanberatedonapresence/absencesystem.InAustralia,theleavesonthethirdtofifthmainstemnode(downfromtheplantterminal)arethebesttosample.
Thegeneralthresholdformitesformostofthegrowingseasonis30%ofplantsinfected.Thethresholddependsmoreonwhenmitepopulationsbegintoincreaseandhowquicklytheyincreaseratherthanthenumberofmites.Toestimatethepercentageofyieldreductioncausedbymites,acharthasbeendevelopedbythecottonindustryforthedifferentcottongrowingregions.
Management
UnderAustralianconditions,mitepopulationsincreaselessrapidlyontheokraleafvarietiesthanbroadleafvarieties.
Miteinfestationsincreaseaftertheapplicationofsomebroad-spectruminsecticidesforcontrolofotherpests.
Controlweedswithinfieldsandalongfieldboundariesthatserveasover-winteringsitesformites.
ForchemicaloptionstocontrolmitesseethelatestCottonCRC'spestmanagementguide.
Thripsarethemajormitepredatorincotton.Othersincludedamselbug,bigeyedbug, ladybirdbeetles, brownsmudgebug, appledimplingbug, brownlacewingadults,and tanglewebspiders.
Mirids(Creonitiadesspp)
Animportantsuckinginsectpestofcotton,miridsareabundantincottonfromearlytomidseasonandoccurthroughoutthecottongrowingregionsofQueenslandandNewSouthWales. Greenmiridsaremorecommonthanbrownmiridsbutbothcausesimilardamage.
Damage
Adultsandnymphsfeedbypiercingplanttissueandreleasingachemicalthatdestroyscellsinthefeedingzone,resultinginthefollowingsymptoms:
localisedleafdamage
terminalwiltingofyoungplants
deformity(broomshaped)
sheddingofsquaresandsmallbolls
damagetobolls(upto15 daysold)bycausingwartygrowthsinsidecarpelwhichcausesdiscolouredlint
malformedbolls,delayofmaturity
reducedlintandfibrequality.
Monitoringandthresholds
Miridsareaverymobilepestandpopulationscanfluctuaterapidlysosamplingneeds
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