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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
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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
Weeds|53
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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The Sunflower Production Guide
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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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The Sunflower Production Guide
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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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