55CONTROL TIPS

Noin-cropherbicidesareavailableforcontrolofcockleburinsunflower.Cockleburplantsareshorterandaretypicallynotharvestedwiththesunflowerseed.Useofanall-cropheaderincreasesthepotentialforcockleburseedstobecollectedasitcutsclosertotheground.Croprotationswithsmallgrainsandcultivationhelpmanagecockleburproblems.

Figure 55. Mature cocklebur plant

The Sunflower Production Guide

WEEDSWeedscompetewithsunflowersforresources,limitingcropgrowthandreducingyield.Yieldlossescausedbyweedcompetitionisafactorofweedspecies,density,relativetimeofemergencetothecropandenvironmentalconditions.Weedspeciesdifferincompetitiveability;somecausinghigheryieldlossesonaperplantbasis.

Sunflowersareagoodcompetitoroncethecropisestablished.Weedcompetitionduringtheearlystagesofgrowthhasthelargestimpactonyield,thustheCriticalPeriodofWeedControlinsunflowersisV-EtoV-4.

Thefollowingweedsectionscontainsinformationonspecificweedspeciesthataredifficulttocontrolinsunflower.

Cocklebur

Cockleburhastheabilitytoreducecropyieldsandqualityconsiderably.Itisanannualplantthatusuallygrowsinrangelands,alongroadsides,andinwasteareas.Cockleburissaidtobeoneofthebiggestforeignmaterialproblemsforconfectionarysunflowerprocessors.

Quick ID

Seedling –Longandnarrowcotyledons.Thestembelowthecotyledonsispurplishgreen.Firsttrueleavesaretriangularwithtoothedmargins.Iftheplantispulledup,theremainsoftheburcanbeusedtoconfirmseedlingidentification.

Juvenile–Cockleburhasanerect,ridged,rough-hairystemwithpurplishspots.Leaveshavethreemainveinsandareheart-shapedortriangular.Leavesandstemsareroughtothetouch.

Mature–Femaleandmaleflowersareonthesameplant,butareseparate.Themaleflowersaresphericalandnon-spiny.Thefemaleflowerisgreenandspiny.Ifcrushedtheplantgivesoffadistinctiveodor.

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The Sunflower Production Guide

52|Weeds

CONTROL TIPS

Biennialwormwoodhasnaturaltolerancetomanysoil-appliedandpost-emergencebroadleafherbicides.Wherepossible,pre-emergentfollowedbypost-emergentherbicideapplicationsarethemosteffectivestrategytocontrolbiennialwormwood.Sinceitcangerminateseasonlong,asoilappliedherbicidewithprolongedresidualactivityisneededtoprovideoptimalmanagement.

Sulfentrazonehasshowntohaveupto80%controlofbiennialwormwoodinNDSUtrials,butnodatatosupportthathasyetbeenestablishedinCanada.

Post-emergentherbicidesmustbeappliedtoseedlingslessthan8cmtall.Noin-cropherbicidesareregisteredforcontrolofbiennialwormwoodinsunflower.Forthisreason,croprotationandplanninginpreviouscropsisimportanttomanagetheweed.RefertotheGuidetoCropProtectionforproductsthatcancontrolbiennialwormwood.

Biennial Wormwood

Anative,prolific,small-seededweedforwhichbothannualandbiennialtypescoexist.Traditionally,biennialwormwoodhasbeenclassifiedasanon-croplandweed,andthereforereceivedlittleattentionasamajorarable-landweed.Plantstypicallygrow3to7feettallwithawoodystemaveraging1to2inches(3to 5 cm)indiameter.

Seedlingemergencecanoccurduringtheentiregrowingseasonunderfavorableconditions.Theplantgrowsslowlyafteremergence,remainingasarosetteuntilmidsummer,afterwhichgrowthbecomesrapid.Biennialwormwoodisoftenconfusedforcommonragweed.

Quick ID

Seedling–Cotyledonsareovaloroblongandverysmall(2to3mm).Firsttwoleavesareopposite,ovaltoelongatedhaving2smallteethontheleafmargin.

Juvenile –Formsabasalrosette,short-stalked,pinnatelydividedandre-dividedleavesthatarecoarselytoothed.

Mature –Erect,hairlessplant,withaslenderstemandlittletonobranchinggrowing10to175cmtall.Leavesappeartoformawhorlaroundthestem.Green,inconspicuousclustersofflowersdeveloponshortbranchesintheaxilsofsmallleavestowardsthetopofthestem.Whentheupperleaves,stemandflowerheadsarecrushed,theygiveoffanodorresemblingacombinationofsageandcarrot.

Biennial Wormwood VS. Common Ragweed

Biennialwormwoodhavehairlessleaveswithsharpedges,whereascommonragweedleavesaresmooth,hairyandhaveroundedges.

Figure 56. Biennial wormwood seedling

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Canada Thistle

Isaveryaggressivecreepingperennialthathasthepotentialtocausesignificantyieldloss.Canadathistlespreadsprimarilybyadeep,horizontal,creepingrootsystemformingdensepatches.Itthrivesinawiderangeofsoiltypes,growingbestindisturbedareasandovergrazedpasture.Asingleplantcanproduceover6mofrhizomeperyear.ItistheseundergroundrootsthatmakecontrolofCanadathistledifficult.Canadathistlehasseparatemaleandfemaleplants,whereonlythefemaleplantsproduceseed.Eachplantmayproduceover40,000seeds,whichcanremainviableinthesoilfor21years.

Quick ID

Seedling-Oblongtobroadlyovalcotyledons.Shootsthatemergefromundergroundrootbudslackcotyledons.Firsttrueleavesareovatewithsharpspinesalongmargins(Figure57).

Juvenile-Irregularlylobedleaveswithspinesonlyonthemargins.Plantsvaryintheextentoflobing,lengthofspinesonmarginsandthepresenceorabsenceofhairontheundersidesoftheleaves.Uppersurfaceisshiny.

Mature –Headsformattheendofstemsinclustersmadeofnumerouspinkishpurplediscflowers.Bractsareflattenedandendinshort,weakprickles.

Stemsarehollow,erectandsmooth;spinesmaybepresentnearthebaseoftheplant.

The Sunflower Production Guide

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CONTROL TIPS

MostofthebiomassofCanadathistleplantsisbelowground;thereforekillingtherootsistheonlyeffectivecontrolmethod.Anintegratedmanagementplanisrequiredtoreduceinfestations.Rhizomesareunaffectedbycultivationastheygrowbelowthenormaltillagedepths.Rhizomeshigherinthesoilprofilethatarebrokenbytillagewillproducesmallrootpiecesthatrapidlydevelopintonewplants.Repeatedmowingoftheinfestationthroughoutthegrowingseasonoverseveralyearswilldepletethefoodenergystoredintherootsystem.AvarietyofherbicidesareavailableforcontrollingCanadathistle,butresidualherbicidesaremoreeffective.Fallapplicationsmaximizetranslocationofthechemicalintotherootssincetheplantisputtingreservesintotherootsystemtosurvivethewinter.Springapplicationsjustcausere-sproutingoftheplants.Mosteffectivecontrolisthroughacombinationofspring-summermowing,followedbyafallherbicideapplication.

Figure 57. Canada thistle seedling

Figure 58. Juvenile Canada thistle

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54|Weeds

Kochia

Kochiaisanannualplant,originallyintroducedasanornamentalgardenplant.Sincethen,kochiahasbecomeamajorweedprobleminmanyareasofCanadacausingseverereductionsinyield.

Quick ID

Seedling–Cotyledonsareshortandnarrow,dull-greenontheuppersurfaceandbrightpinkontheunderside.Thefirstleaveshavemanysofthairs.Plantsformabasalrosettewhennotincompetitionwithothervegetation.

Juvenile–Hasanerect,purple-stripedstemthatisheavilybranched.Leavesretainthegreyish-greenappearanceandarehairy.

Mature–Leavesbecomemuchsmallertowardsthebranchtipsresultinginapyramid-shapedplant.Flowersaregreen,lackpetals,andareinconspicuousinleafaxils.Thewholeplantturnsbrightredinthefall.Whentheplantdries,thestembreaksoffatgroundlevelandactsasatumbleweed,scatteringseedsalongitspath.

CONTROL TIPS

Kochiaseedsremainviableinthesoilforapproximatelytwoyears.Forthisreason,preventingseedproductionforafewyearswillnearlyeradicatepopulations.Toadequatelycontrolkochia,anintegratedapproachisrequired.Falloworshorttermperennialforageproductionpreventsseedproduction.Seedlingsarecontrolledbylate-springcultivation.Sulfentrazone(Authority),apre-seedherbicide,isregisteredtocontrolkochia.Mowheavypatchesofkochiainsalineareastopreventseedproduction.Whensprayingseedlings,itisimportanttomaintainwatervolumesintheupperrecommendedrangestoachievesufficientcoverageandpenetratehairsontheleafsurface.Itisimprotanttorotateherbicidegroupsaskochiacanquicklydevelopherbicidetolerance.

Figure 60. Kochia seedlings

Figure 61. Kochia seedlings have densely haired leaves.

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The Sunflower Production Guide

Prairie Sunflower

Wildsunflowergrowstoaboutthesameheightascultivatedsunflower,competingforsunlight,spaceandmoisture.Itisahosttopestsofcultivatedsunflower,reducingyieldandquality.

Quick ID

Seedlings –Oblongcotyledonsandoppositelyarrangedfirstleaves.Oftenfoundonsandiersoils.

Juvenile–Leavesarelanceolatetoovateinshapewithawavymargin,whereasannualsunflowershavedistinctlytoothedmargins.Prairiesunflowerstemsarecoveredwithshorthairs,flattenedtothesurface.Thisiscontrastingtoannualsunflowerswhicharebristlytothetouch.

Mature–Theheadsofprairiesunfloweraresmallerthanannualsunflower.Thecentraldiskflowersarepurplishbrownandflattened.

62CONTROL TIPS

Pre-plantburndownisnecessaryusinganyofthelabeledproducts.SoloorOdysseysprayedinCLEARFIELDhybridsonlyandExpressinExpressSunhybridsonly,hasshowntoprovidecontrolofPrairieSunflower.Applicationoftheseherbicidesinnon-toleranthybridswillcauseextensivedamage.IftherearemanywildsunflowersgrowinginCLEARFIELDorExpressSunsunflowercrops,controlofthewildspeciesisessentialtopreventcross-pollinationwhichcouldcausethewildsunflowertodeveloptolerancetotheseherbicides,diminishingtheeffectivenessofthesetechnologies.ContactyourlocalseeddealertofindoutmoreabouttheCropStewardshipProgram.

Figure 62. Wild sunflower

Figure 63. Wild sunflower leaves have a wavy margin.

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CONTROL TIPS

Betweenrowcultivationorhoodedsprayerherbicideapplicationcanbeusedforcontrolin-crop.Pre-emergentherbicideapplicationsincludingGlyphosateadditionsoffergoodcontrol.Severalpre-seedherbicidesareregisteredandachievefairtogoodcontrolofwildbuckwheat.In-cropherbicidessuchasAssertareratedfairtogood.Bestcontrolisachievedwhenplantsare3inchesorsmaller.ConsultthecurrentGuidetoCropProtectionforupdatedinformationonregisteredherbicidesandapplicationinformation.

Figure 64. Wild buckwheat has arrow shaped leaves.

Figure 65. The cotyledons of wild buckwheat are angled at 120 degrees.

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Wild-Buckwheat

AnannualintroducedfromEuropeincontaminatedseed,thistwiningnaturedplantmakesfieldworkdifficult.Althoughnotascompetitiveinsunflowercomparedtoothercropslikewheat,asignificantseedbankcanbeproducedinsunflowercreatingproblemsinfutureyears.

Quick ID

Seedlings–Linearcotyledonsattachedat120degreestooneanother.Thestembelowthecotyledonsisoftenreddishpurple.Thetrueleavesarearrowshapedwithpointytipsandpointedbasallobes.Apaperysheathisfoundatthebaseofthefirstleaves.

Juvenile–Twininggrowthhabit,slenderstembranchesnearthestem.Tanglingwithcropscancauselodgingandmakeharvestdifficult.

Mature–Greenishpinkflowersareproducedinaxillaryandterminalclusters.

Fieldbindweedandwildbuckwheatareoftenconfused.Thecotyledonsoffieldbindweedareround,leaveshavearoundedtip,lackssheathatthestemnodes,andhasatrumpet–shapedflower.

The Sunflower Production Guide

Redroot Pigweed

Redrootpigweedisacommonweedofcultivatedfields,gardens,andwasteareas.Thisweedhasanextendedgerminationperiod,growsrapidly,andhasahighrateofseedproduction.Redrootpigweedthrivesandcanquicklyout-competesufferingcrops.

Quick ID

Seedlings–Longnarrowcotyledons.Firsttrueleaveshaveanotchedtip,intowhichthemidribextendsasasmallbristle.Thecotyledonsandfirsttrueleavesareredontheunderside.Thetaprootandstemsarealsored.

Juvenile–Erectstems,usuallyhairyandgreennearthetopoftheplantwhilegreenandsmoothnearthebase.Theleavesarediamondshaped,withentiretoslightlywavymargins.Prominentwhiteveinsontheundersideoftheleaf.

Mature–Tinygreenflowersdevelopinbristlyspikesatthetopoftheplant.Theylookandfeelbristly.

CONTROL TIPS

Controlofredrootpigweedisrequiredcontinuallythroughoutthecroprotation.Authorityhasexcellentcontrolandcanbeusedinreducedandnotillagesystems.TheCLEARFIELDandExpressSunsystemsalsoachieveexcellentcontrol.ConsultthecurrenteditionoftheGuidetoCropProtectionforproductinformationandapplicationtips.Inter-rowcultivationorinter-rowhoodedsprayerapplicationscanalsobeemployedforcontrol;chemicalcontrolismostefficaciouswhenmadepriortothe4-leafstage.

Figure 66. Mature redroot pigweed plant

Figure 67. The underside of Redroot pigweed seedling leaves are red.

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CONTROL TIPS

Manyofthepre-seedherbicidesregisteredforsunflowersachievegoodcontroloffalseragweed.Glyphosateburndownatplantingandcultivationarethemostcommoncontrolmethods.Althoughitusuallygerminatesbeforethecrop,acoolspringcandelaygermination.Fewpost-emergentcontroloptionsareavailable.CLEARFIELDsunflowersutilizingOdysseyachievesgoodcontrolandhasresidualactivityforprolongedcontrol,butnotaslongassomeother“imi”herbicides.Cautionisneededwithuseofresidualherbicidesanditisimportanttomanageacroprotationtoavoidplantinganimi-sensitivecropwithintherecommendedtimeperiod.SeetheGuidetoCropProtectionformoredetails.

Figure 68. Mature false ragweed plant.

Figure 69. False ragweed seedling leaves are hairy.

The Sunflower Production Guide

False Ragweed

Alsoknownasmarshelder,falseragweedisarobust,competitiveannualweedofroadsidesandwasteareasthatcangrowupto2mtall.Itproduceslargeamountsofpollencausinghayfever.Whennotinflower,falseragweedresemblessunflowers.

Quick ID

Seedling –Cotyledonsareovalandstalked.Thefirsttrueleavesareopposite,variablylobedwithasoft,hairytexture.

Juvenile–Stemsaresmooth,muchbranchedanderect.Lowerleavesareoftenthree-lobedwhereastheupperleavesarebroad,almostheart-shaped,withcoarseirregular-toothedmargins.Leavesarecoveredwithhairsonbothsurfaces.

Mature–Small,greenishwhiteflowersinbranchingclustersatthetopoftheplant.

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The Sunflower Production Guide

Green and Yellow Foxtail

AnnualsintroducedfromEurope,greenandyellowfoxtailareseriousweedsofcultivatedcrops,gardensandroadsides.Seedsgerminatethroughoutthegrowingseasonwheneverconditionsarefavorable,makingcontroldifficult.

Quick ID

Green Foxtail

Seedling–Thefirstleavesarearchedandhairless.Baseoftheseedlingisoften reddish.

Juvenile-Leafbladesareflatandlightgreen.Themarginsanduppersurfaceofleafbladesmayfeelslightlyroughtothetouch.Theligule(membraneattheinnerbaseoftheleafwheretheleafattachestothemainstem)hasanunevenfringeofhairs.Auriclesareabsent.

Mature–Soft,greenorpurple-tingedbristlyspike-likepanicleresemblesabottlebrush.

Yellow Foxtail

Seedling –Arched,hairlessearlyleaves.Baseoftheseedlingisoftenreddish.

Juvenile –LeafbladesareflatorV-shapedandlooselytwisted.Bladesarehairlessexceptforlong,kinkyhairsontheuppersurfaceoftheleavesnearthebaseoftheblade(completelylackinginGreenfoxtail).Auriclesareabsent.Liguleisafringeofhairsabout3mmlong.

Mature–Spikeletsarelargerthanthoseofgreenfoxtail

CONTROL TIPS

Pre-plantherbicideoptionsareavailablethatcanprovidegoodtoexcellentcontrolofboththeseweedspecies.Post–emergentherbicidesareavailablethatprovideexcellentcontrol.ConsultthecurrentissueoftheGuidetoCropProtectionforcontroloptions.Maintainingwatervolumeisimportanttoachieveadequatecoveragesincetheleavesarenarrow.

Figure 70. Green foxtail seedling have light green leaves and are completely hairless.

Figure 71. Collar region of Yellow foxtail has long hairs on the upper leaf surface.

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