Fact Sheet No. 5.578 Insect Ser ies|Crops

Quick Facts•FourspeciesofmitesattackwheatinColorado.

• Thewheatcurlmiteeggs,immaturestagesandadultsarefoundinthewinteronwheatandnearbyperennialgrasses.

•Brownwheatmitesummersinthesoilasawhiteegg.Inthefall,eggshatchaftera10-dayincubation.

•Banksgrassmitesproduceheavywebbingtoprotectcoloniesofeggsandadults.

• Favoredhostsofthewintergrainmiteincludesmallgrainsandgrasses.

©ColoradoStateUniversityExtension.9/99.Revised12/14.

www.ext.colostate.edu

Four species of mites attack wheat in Colorado:• Thewheatcurlmite,Aceria tosichella,

is a microscopic eriophyid mite of great economic significance in Colorado. It vectors the causal agents of wheat streak mosaic (Figure 1) and high plains disease.

• Thebrownwheatmite,Petrobia latens,andBanksgrassmite,Oligonychus pratensis,arespidermitesthatoccasionally cause economic damage to winter wheat in Colorado. Brown wheat mite infestations normally are associated with dry spring weather and usually disappear with significant precipitation.

• Banksgrassmitebecomesapestofyoungwheat when it moves off maturing corn inthefall,andlesscommonlyinthelatespring during droughty periods.

• Wintergrainmite, Penthaleus major,alsodamageswheat,butisrareinColorado.

by F.B. Peairs*

Mites in Wheat

*Colorado State University Extension entomologist and professor; bioagricultural sciences and pest management. 12/2014

Wheat Curl MiteField Biology. Eggs,immaturestagesand

adult wheat curl mites (Figure 2) are found inthewinteronwheatandothernearbyperennial grasses. As temperatures rise in thespring,mitepopulationsdevelopunderleafsheaths,insidenewlyemergedleaves,

Figure 1:Wheatplantaffectedbywheatstreakmosaic.PhotographbyR.Hammon.

Figure 2:Wheatcurlmitesinveinsofwheatleaf.

and eventually on green tissues in the head. Eggs are placed along leaf veins. An average complete generation requires eight to 10 days. Most mites are found on the upper surface oftheyoungestfullyexpandedleaf,adjacenttotheligule.Theyseemtopreferthemosttender leaf tissue and therefore move to each new leaf as it emerges. Leaf curling occurs asatightrolloftheleafmargin,incontrasttothelooserrolloftheentireleafcausedbyRussian wheat aphid.

Asthewheatplantdriesdown,thewheatcurl mites congregate on green tissue in the upper parts of the plants where they are pickedupbywindcurrentsandcarriedtotheir oversummering grass hosts. As summer hostsstarttodrydown,thereverseprocessoccurs,andmitesarecarriedbywindstonewly emerged winter wheat.

Host Plants.Thewheatcurlmiteattacksawidevarietyofgrasses,mostlyinthe Agropyron, Alamos, Hilary, Hordeum, Lolium, Muhlenbergia,Poa, Stipa, Triticum and Zeagenera.Corn,volunteerwheatandsummergrassyweedssuchasbarnyardgrass,stinkgrass,witchgrassandgreenfoxtail,areimportant oversummering hosts in Colorado.

Distribution.ThismiteisknowntobewidelydistributedinEuropeandNorthAmerica,includingthewheat-producingareas of Colorado. It is likely found in most wheat-producingareasoftheworld,sincewheat streak mosaic occurs in these areas.

Scouting and Treatment.Theonlyeffective and economical controls for wheat

curlmitearepreventive,soscoutingisnotneeded. Use preventive controls in high risk areaswherewheatwasdamagedbyhailafter heading or where wheat will emerge beforeadjacentcorndriesdown.

Destruction of volunteer wheat and the maintenanceofatwo-weekvolunteer-freeperiod prior to planting winter wheat in the fall are the most effective management practices for this mite and the virus diseases that it vectors. Some effective varietal resistanceisavailable.

Control of wheat curl mites with foliaracaricideshasnotbeenshowntobe effective.

Figure 3:Wheatplantdamagedbybrownwheatmite.Mitescanbeseenonleaves.

Figure 4:Redbrownwheatmiteeggs,indicativeofactivepopulation.

Figure 5:Whitebrownwheatmiteeggs,indicativeofpopulationgoingintosummerperiodofinactivity.

yieldmaybesoreducedbydroughtastomake chemical treatment uneconomical. Also,ifwhiteeggsarepresentandredeggsaremostlyhatched,thepopulationis in natural decline and treatment is not economically justifiable.

Banks Grass MiteField Biology. Fertilized female Banks

grass mites move into winter wheat in the fallastheirsummerhosts,primarilyfieldcorn,begintodrydown.Overwinteringmitesarebrightorange.Withtheonsetofwinterconditions,themitesmovetothecrownsofwheatplants,wheretheyfeeduntilspring.Small,pearlywhiteeggs then are laid that mature into pale to brightgreenmaleandfemaleadults.Mitesbreedcontinuouslyonwheatandsummerhosts until their return to winter wheat inthefollowingfall.Thetimerequiredto complete a generation varies with temperature and is usually 10 to 20 days.

Banks grass mites produce heavy webbingtoprotectcoloniesconsistingofeggs,immaturesandadults(Figure6). Colonies usually are found on the undersides of leaves. Damaged leaves first becomeyellow,thenbrownandnecrotic.Heavy populations can kill small plants and reduce kernel size in larger plants.

Host Plants. Banks grass mite attacks awidevarietyofgrasses.InColorado,itisconsideredtobeaseriouspestofcornandanoccasionalpestofturf,sorghumand wheat.

Distribution. Banks grass mite has beenfounddamaginggrassesinmanyparts of the Americas and Africa. It is foundthroughoutthegrain-growingareasof Colorado.

Scouting and Treatment. Banks grass mite most commonly damages Colorado winter wheat in the fall in areas near maturing field corn. Insecticide applications tofieldmarginsborderingcornoftenaresufficient to prevent economic damage. Spring infestations are not common in the state. Information on miticides registered foruseagainstbrownwheatmitecanbefound in the High Plains Integrated Pest ManagementGuide,https://wiki.bugwood.org/HPIPM:Main_Page.

Winter Grain MiteField Biology.Wintergrainmite

hastwogenerationsperyear.Thefirstbeginsinthefallastheoversummeringeggs hatch after rains provide adequate

Figure 6:Banksgrassmitefemaleandeggs.

Brown Wheat Mite Field Biology. Brown wheat mite

(Figure 3)spendsthesummerinthesoilasawhiteeggresistanttohot,dryconditions.Inthefall,ascooler,wetterconditionsreturn,theseeggsstarttodevelopandhatchaftera10-dayincubation.Femalemites mature after feeding on wheat for abouttwoweeksandthenlayround,redeggs (Figure 4) that give rise to further fall (one or two) and spring (two or three) generations.Maleshavenotbeenobservedin this species. As summer conditions return,whiteoversummeringeggsareproduced. Both red and white eggs are placedonsoilparticlesadjacenttowheatplants (Figure 5).

Brown wheat mites feed on plant sap during the day and spend the night inthesoil.Theiractivitypeaksataboutmidafternoononwarm,calmdays(thebesttimetoscout).Thismiteisnotaffectedbycoldtemperatures,butpopulationsarequicklyreducedbydrivingrainsof1/3inchor more.

Host Plants.Damagefrombrownwheatmitehasbeenreportedfromawidevarietyofcultivatedplants,includingsorghum,onions,fruittrees,carrots,cotton,lettuce,iris,alfalfaandclover.InColorado,thismiteisconsideredtobeapestprimarilyofdrought-stressedwinterwheatandKentuckybluegrassturf.

Distribution. Brown wheat mite is a pestofsmallgrainsinmostsmallgrain-producingareasoftheworld.InColorado,itismostcommonondrought-stressedwinter wheat on the eastern plains.

Scouting and Treatment. Management of volunteer wheat is an important preventivemeasureforbrownwheatmite,asitiswithseveralwinterwheatpests. Any management practices that serve to minimize drought stress are also important.Onceanoutbreakoccurs,however,chemicalcontrolistheonlyeffective management.

Theeconomicthresholdforthispestisnotwelldefined,butitisatleastseveralhundredmitesperrow-footintheearlyspring.Thisfigurewillincreasewithlower wheat prices and decrease with higher wheat prices. It often is difficult to justifyachemicaltreatment,sincebrownwheat mite infestations are associated with drought stress. If a driving rain of atleast1/3inchoccurs,mitelevelswillbesignificantlyreducedregardlessofchemicaltreatment.Ifitdoesnotrain,crop

ColoradoStateUniversity,U.S.DepartmentofAgricultureandColoradocountiescooperating.CSUExtensionprogramsareavailabletoallwithoutdiscrimination.Noendorsementofproductsmentionedisintendednoriscriticismimpliedofproductsnotmentioned.

moisture.FeedingpeaksinDecemberorJanuary. Second generation feeding peaks in March or April. Populations decrease and oversummering eggs are produced as temperaturesbecomeunfavorablywarm.

Newly-hatchedmitesfeedonleafsheaths and tender shoots near the ground. Olderimmaturesandadultsfeedhigherupon the plants at night and on cloudy or cool days.Theymovetothesoilsurfaceandintothe soil to seek moisture and to avoid warm temperatures.Wintergrainmiteactivityisgreatestbetween40and70degreesF.Onhot,drydays,itmaybenecessarytodig 4 to 5 inches into the soil to find the mites.Themitesarenotharmedbyhighhumidity,rainfall,shortperiodsofsleetoricecover,orbygroundfrozentoadepthofseveral inches.

Host Plants. Favored hosts include smallgrainsandgrasses.Wintergrainmitealsohasbeenreportedtodamagelegumes,vegetables,ornamentalflowers,cotton,peanut and various weeds.

Distribution.Wintergrainmiteisfound in temperate areas throughout the world. Since it has higher moisture requirements than other mite pests of winterwheat,thismiteisrarelyapestunder Colorado growing conditions.

Scouting and Treatment. Scout for winter grain mite early in the morning or duringcool,cloudyweatherwhenthismiteismostlikelytobevisible.Checkformitesunder crust and clods on the surface of moistsoilunderwheatplants.Underhot,dryconditions,scoutseveralinchesunderthe soil.

Littleisknownaboutwintergrainmitemanagement.Infestationsprobablyshouldexceedseveralmitesperplantbeforechemical treatment is considered. Crop rotation is important.

Field Key to Mites Attacking Small Grains• Leaves with tightly rolled edges. Plants

withchloroticspecklesorstreaks,oftenstunted(symptomsofWheatStreakMosaic)(Figure1).Tiny,wormlikemites,visiblewithaidofhandlens(atleast10X),presentonleaves.Oftenfoundinspacesbetweenveins(Figure 2).Wheat curl mite.

• Leaves finely mottled and may have chlorotictips(Figure3).Heavilyinfested crops have a droughty appearance,orayellowishtobronzeddiscoloration.Onwarm,calmdaysbrownmiteswithextremelylongfrontlegs(Figure3)maybefoundonleaves,otherwisetheycanbefoundundersoilorsurfacedebris.Brown wheat mite.

• Leaveschlorotic,smallplantsmaybekilled. Damaged areas on larger plants mayhaveabrightyellowappearance.Infested plants in the fall are often near drying corn. Small green mites (Figure 6) on leaves or in crowns. Produces noticeableamountsofwebbingonundersidesofleaves(brownwheatmitealso may produce small amounts of webbing).Banks grass mite.

• Heavily infested crops grayish or silvery. Plantsmaybestunted.Leaftipsappearscorched and entire leaves or plants can bekilled.Absenceofyellowmottlingtypical of spider mite feeding. A large darkbrowntoblackmite,withreddishlegs.Atanororangespotisoftenvisibleontheback.Winter grain mite.

Chemical Control of Mites in Wheat

• Scoutandidentifythepestspeciesthatarepresent.

• Decideifitiseconomicaltoapplyachemicaltreatment.

• ConsultthecurrentHigh Plains Integrated Pest Management Guide for Colorado, Montana, Western Nebraska and Wyoming, www.highplainsipm.org,forthetreatmentortreatmentcombinationthatprovidesthebestoverallcontrolofthepestproblemsthatarepresent(forexample,mitesalone,mitesplusRussianwheataphid,mitespluscutworms).Thebestchoicedependsonthepestcombination.

• Useatleast2gallonsperacretotalsprayvolume,especiallyifBanksgrassmiteispresentinthespring.

• Useasurfactant.

• BufferthespraysolutiontopH7orlower.Dimethoate(variousformulations)shouldbebufferedtopH5.

• Treatwhenseveralhoursoftemperaturesabove50Fareexpected,especiallyifusingdimethoate.

• Evaluatetreatmenteffectiveness.