JOSEPHM.DITOMASO WeedScienceProgram,DepartmentofPlantSciences UniversityofCalifornia,Davis GUYB.KYSER DepartmentofPlantSciences,UniversityofCalifornia,Davis MICHAELJ.PITCAIRN BiocontrolProgram,IntegratedPestManagementBranch CaliforniaDepartmentofFoodandAgriculture,Sacramento Publishedbythe CaliforniaInvasive PlantCouncil September2006 YellowStarthistle Management Guide USArmyCorps ofEngineers Engineer Research and Development Center YSTMgmt(FINAL).indd 1 10/12/06 12:49:19 PM ACKNOWLEDGEMENTS Development of this management guide was one of the long-term goals of a re- searchdemonstrationprojectonIntegratedWeedManagementofYellowStarthistle atFortHunterLiggett,CA.TheauthorsaregratefultotheDepartmentofDefense LegacyResourceManagementProgramforpartialfundingthroughLegacyProject ModelInvasiveSpeciesControlProject:YellowStarthistle(LegacyProject#01-160 and03-160)underMIPRW31RYO30983808,andtheU.S.ArmyEnvironmental Center for their financial support of the project, and to the Western Integrated PestManagementCenter“IPMIssues”programfortheirfinancialsupportofthe preparationandpublicationofthismanagementguide. Theauthorsalsothankthemanypeoplewhoassistedinthedevelopmentand completionoftheFortHunterLiggettproject.Dr.StevenR.Bennett,U.S.Army Environmental Center, provided leadership on the the project’s vision and orga- nization.Dr.AlCofrancesco,U.S.ArmyCorpsofEngineers,EngineerResearch andDevelopmentCenter,andDr.HerbBolton,U.S.DepartmentofAgriculture, CooperativeStateResearch,Education,andExtensionServiceliaisontotheU.S. ArmyEnvironmentalCenter,assistedwithtechnicalcoordinationfortheproject. Mr.KennethSpencer,formerIntegratedTrainingAreaManagementCoordinator and Mr. Arthur Hazebrook, Integrated Training Area Management Coordinator, U.S. Army Combat Support Training Center, Fort Hunter Liggett Training Site providedlogisticalassistanceandmuchoftheresearchatFortHunterLiggett.Don Joley and Baldo Villegas of the California Department of Food and Agriculture, BiologicalControlProgram,assistedwiththereleasesandmonitoringofthebio- logicalcontrolinsects.DaleWoodsandViolaPopescu,alsowithCDFA’sBiological ControlProgram,performedthereleasesoftheMediterraneanrustdiseaseatFort Hunter Liggett. We also thank Jessica Miller for her diligent work on her M.S. degreestudyingyellowstarthistleatFortHunterLiggett. RECOMMENDEDCITATION DiTomaso,J.M,G.B.Kyser,andM.J.Pitcairn.2006. Yellowstarthistlemanagementguide.Cal-IPCPublication2006-03. CaliforniaInvasivePlantCouncil:Berkeley,CA.78pp.Available:www.cal-ipc.org. CONTACTINFORMATION Toobtaincopiesofthisreport,contactthe CaliforniaInvasivePlantCouncilthroughitswebsite,www.cal-ipc.org. EditedbyDougJohnsonandElizabethBrusati,Cal-IPC PhotosbyJoeDiTomaso,UCDavis,unlessotherwisenoted DesignedbyMelanieHaage Copyright©2006byCaliforniaInvasivePlantCouncil YSTMgmt(FINAL).indd 2 10/12/06 12:49:21 PM Chapter1.IntroductionandSpread............1 IntroductiontoNorthAmerica.........1 SpreadandDistributioninCalifornia ......1 SpreadtoOtherStates .............2 MechanismsofSpread .............3 Chapter2:Impact.....................4 Economics....................4 Rangelands ...................4 ToxicitytoHorses................5 RoadsidesandRecreationalAreas ........5 Wildlands....................6 WaterConsumption ...............6 BeeIndustry ...................7 Chapter3:BiologyandEcology..............8 TaxonomyandIdentification ..........8 Reproduction..................8 GerminationandDormancy ...........11 GrowthandEstablishment...........12 Light,Temperature,andWaterUsePatterns..14 Management ...................16 Chapter4.MechanicalControl .............17 HandPullingorHoeing.............17 Tillage......................18 Mowing .....................19 Chapter5.CulturalControl...............21 Grazing......................21 PrescribedBurning................23 Revegetation...................27 Chapter6.BiologicalControl..............32 NaturalEnemiesAssociatedwith YellowStarthistleControl...........34 CurrentStatusofYellowStarthistleBiological Control.....................36 ChoiceofBiologicalControlAgents.......37 MethodsandTiming ...............37 MonitoringSeedHeadInsects..........38 Economics....................39 Risks.......................39 Chapter7.ChemicalControl ..............41 Economics....................41 MethodsandTiming ...............41 HerbicideApplicationTechniques ........49 Risks.......................50 Chapter8.DevelopingaStrategicManagementPlan.. 53 Prevention .................... 53 Eradication ................... 54 DevelopingaManagementStrategy ....... 54 ImplementingaStrategicPlan ......... 59 ExamplesofIntegratedManagementStrategies 59 Conclusion .................... 63 LiteratureCited.................... 64 Tables Table1.Comparisonofgrazingcharacteristicsof cattle,sheep,andgoats..............22 Table2.Distribution,impacts,andpublications onyellowstarthistleseedheadinsects...... 33 Table3.Commonlyusedherbicides........... 42 Table4.Summaryofcontroloptions .......... 55 Figures Fig.1.ExpansioninCalifornia. .............2 Fig.2.Soilmoistureunderyellowstarthistlecompared toannualgrasses...................2 Fig.3.Viableseedproductioninrelationtoflowering stage.........................11 Fig.4.Seedbankinrelationtoyearlyrainfall.......11 Fig.5.Germinationinrelationtorecentrainfall.....11 Fig.6.Declineinseedbank. ............... 11 Fig.7.Growthofrootsandrosettes............ 13 Fig.8.Effectofsoildepthoncover. ........... 14 Fig.9.Effectofshadingonrootgrowth.......... 14 Fig.10.Effectofshadingonrosettegrowth. ...... 15 Fig.11.Effectofsunlightonbiomassproduction. ...15 Fig.12.Effectofmowingheightonseedheads. .... 19 Fig.13.Effectofcoveronbranchinghabit........ 20 Fig.14.Effectofburningoncover............24 Fig.15.Effectofburningonsoiltemperature...... 25 Fig.16.Effectofburningonseedbank.......... 26 Fig.17.Competitionwithperennialgrasses.......26 Fig.18.Effectofinsectcontrolagentsonseedproduction. 35 Fig.19.Late-seasoncontrolwithglyphosateandtriclopyr.45 Fig.20.Effectofclopyralidrateandtimingonforage andyellowstarthistle.................46 Fig.21.Effectofstandinglitteroncontrolwithclopyralid.48 Fig.22.Effectivenessofclopyralidwithrevegetation...60 Fig.23.Effectivenessofburningintegratedwith clopyralid....................... 61 Fig.24.Effectofburning+clopyralidonannualgrasses.62 Fig.25.Effectivenessofburningfollowedbyclopyralid treatment........................62 Contents YSTMgmt(FINAL).indd 3 10/12/06 12:49:21 PM YSTMgmt(FINAL).indd 4 10/12/06 12:49:21 PM YELLOWSTARTHISTLEMANAGEMENTGUIDE | 1 IntroductiontoNorthAmerica T hecenteroforiginofyellowstarthistle(Cen- taureasolstitialisL.)isbelievedtobeEurasia, whereitisnativetoBalkan-AsiaMinor,theMiddle East, and south-central Europe (Maddox 1981). Its introduction into NorthAmerica probably oc- curredinCaliforniaafter1849asaseedcontami- nant in Chilean-grown alfalfa seed, known then asChileanclover(Gerlachetal.1998).Historical records indicate that alfalfa was first introduced toChilefromSpaininthe1600sandfromChile toCaliforniaatthetimeofthegoldrush.Despite itsSpanishorigins,alfalfacametoCaliforniaonly fromChilebefore1903.After1903,itislikelythat alfalfa was also introduced from Spain, France, Italy,andperhapsTurkestan. SpreadandDistributioninCalifornia Ithasbeenspeculatedthattheintroductionofyel- lowstarthistleintoCaliforniaoccurredinmultiple steps(Gerlach1997a,b).Thefirstreportofalfalfa cultivationwasnearMarysville,California,in1851. Beforethe1870salfalfawasgrownprimarilyalong riverleveesnearSacramento,Marysville andSan Francisco.Theseareaswerecharacterizedbydeep, well-drainedsoilsandeasyaccesstodrinkingand irrigationwater.Bothanimalandalfalfaforagewere distributedonlyshortdistances.Asaresult,yellow CHA PT ER 1 : IntroductionandSpread Worldwidedistributionofyellowstarthistle.Maddox etal.1985. starthistle infestations that accompanied alfalfa stands were fairly localized. From 1870 to about 1905 much of the surrounding areas previously consisting of dry-farmed wheat and barley fields wereconvertedtobothdrylandandirrigatedalfalfa fields.Duringthisperiod,yellowstarthistleestab- lishedasdenselocalpopulationsintheseareasand alongadjacent roadsides.Theuseoftractorsand other equipment spread starthistle seed to other locations, including grain fields. Gerlach (1997a) indicatesthatyellowstarthistleinCaliforniaprob- ablydecreasedbetween1920and1940,mostlikely duetochangesincropproductiontechniquesand thewidespreaduseofinorganicherbicides,suchas DistributionofyellowstarthistleinCalifornia. This2002map,basedonsurveydatabytownship, illustrateshowwidespreadtheplantisinthestate.At 14millionacres,itisCalifornia’smostwidespreadweed. DatacollectedbytheCaliforniaDepartmentofFoodand Agriculture.(Pitcairn,Schoenig,YacoubandGendron2006) YSTMgmt(FINAL).indd 1 10/12/06 12:49:22 PM SpreadtoOtherStates Introduction of yellow starthistle from California to other western states occurred in the 1870s and 1880s (Gerlach 1997a, Roché 1965). The first report outside of California was in Bingen, Washington (Sheley et al. 1999b).These first in- troductionswerealsolikelythroughcontamination sodiumarseniteandsodiumchlorate,alongroad- sides.However,aroundthe1930sor1940syellow starthistle began to invade foothill grasslands on bothsidesoftheCentralValley.Inthisway,yellow starthistlebecameanintegralpartofthegrazing/ weed dynamicoftherangeland system,inwhich wildlife and livestock participated in the spread oftheplant.By1958,theweedwasestimatedto haveinvaded overone millionacresinCalifornia (MaddoxandMayfield1985). Sincethe1960s,threefactorshavecontributed greatly tothefurtherspread ofyellowstarthistle: anextensiveroadbuildingprogram,increasedsub- urbandevelopment,andexpansionintheranching industry.Thesefactorsallcontributedtotherapid andlong-rangedispersalofseedandtheestablish- ment of new satellite populations (Gerlach et al. 1998).Overthepast40years,yellowstarthistlehas spreadintorangeland,nativegrasslands,orchards, vineyards,pastures,roadsides,andwastelandareas. The infestation area reached nearly eight million acresinCaliforniaby1985(MaddoxandMayfield 1985).Today,itisthoughttohavespreadtoover 15millionacres,andcanbefoundin56ofthe58 countiesinCalifornia(Pitcairnetal.1998b). Fig.2.Soilmoistureunderyellowstarthistlecom- paredtoannualgrasses.Thevolumetricwatercontent ofsoilunderyellowstarthistleisreducedcomparedtosoil underannualgrassesnearUCDavis,July1996(Gerlach 2003). Fig.1.ExpansioninCalifornia.Acomparisonofesti- matedinfestationareainCaliforniashowsarapidexpan- sionoverthelast50years(Pitcairnetal.2006). Distributionofyellowstarthistleinwesternstates. Whileplainsstateshavemanygrasslandweedsthatthreat- enCalifornia,yellowstarthistleisonegrasslandweed spreadingfromCalifornia.Dataprovidedin2001bystate weedcoordinatorsandcompiledbyEricLane,Colorado WeedCoordinator. 2 | YELLOWSTARTHISTLEMANAGEMENTGUIDE YSTMgmt(FINAL).indd 2 10/12/06 12:49:23 PM ofalfalfaseed(Gerlach1997a).Duringthe1920s, yellow starthistle expanded rapidly in grasslands inthePacificNorthweststates.Bythemid-1980s it was estimated to occupy 280,000 acres in Idaho, 135,000 acres in Oregon, and 148,000 in Washington(Sheleyetal.1999b).In1989,therate ofspreadofyellowstarthistlewasdeterminedtobe 7,000to20,000acresofrangelandperyearinthe west(Callihanetal.1989)andby1994itwasesti- matedtobespreadingattwicethatrate(15,000to 50,000acresperyear)(SheleyandLarson1994). Today, yellow starthistle can be found in 23 of the48contiguousstates,extendingasfareast as New York (Maddox et al. 1985). It has also extended into Canada from British Columbia to Ontario.Beyondthiscontinent,yellowstarthistle isnowfoundinnearlyallMediterraneanclimates andmosttemperateareasoftheworld(Maddoxet al.1985). MechanismsofSpread Humanactivitiesaretheprimarymechanismsforthe longdistancemovementofC.solstitialisseed.Seed istransportedinlargeamountsbyroadmaintenance equipment and on the undercarriage of vehicles. Themovementofcontaminatedhayanduncertified seedarealsoimportantlongdistancetransportation mechanisms. Locally, seed istransportedin lesser amountsandovershorttomediumdistancesbyani- malsandhumans.Theshort,stiff,pappusbristles Contaminatedhay.Ifhaycontaminatedwithyellow starthistleismovedoffsite,itcanbecomeasourceofnew infestations.(Photo:J.McHenry) Seeddispersal.Yellowstarthistleseedshavestiffbristles thatattachtofurorclothing,facilitatingdispersal.(Photo: J.Clark) YELLOWSTARTHISTLEMANAGEMENTGUIDE | 3 arecoveredwithmicroscopic,stiff,appressed,hair- likebarbsthatreadilyadheretoclothingandtohair andfur.Thepappusisnotaneffectivelongdistance winddispersalmechanismaswinddispersalmoves seedsonlyafewfeet(Roché1992). YSTMgmt(FINAL).indd 3 10/12/06 12:49:24 PM Economics Y ellowstarthistleisconsideredoneofthemost serious rangeland, grassland, and wildland weedsinthenorthwesternUnitedStates.Itcanalso infestgrainfieldsandotheragriculturalareaswhere seedscancontaminategrainharvestandlowercrop qualityandvalue. Taxpayersincursignificantdirectcostsforboth regionalandstatewidecontrolofyellowstarthistle bypublicagenciesonpubliclands,includingcosts ofmaterialsandlaborfortreatmentssuchaspre- scribed burning, herbicide application and mow- ing.InCalifornia,about0.5millionacresofyellow starthistlearemanagedatabout$25peracrefora costofabout$12.5millionannuallyinmanagement. TaxpayersalsofundtheCaliforniaDepartmentof Food and Agriculture’s biological control program for statewide management of this noxious weed (Jetteretal.2003). Yellowstarthistleisamajorconsumerofground- water, costing the state millions of dollars in lost water for wildlife, agriculture and municipal uses (Gerlach2004).Itcanalsoreducelandvalueand reduceaccesstorecreationalareas(DiTomasoetal. 1998b,RochéandRoché1988). OnmilitarybasessuchasFortHunterLiggett, yellow starthistle can severely impact training ex- ercisesandcanimpairtheuseofequipment(e.g., snagged parachutes, torn clothing) or clog air fil- tersonvehicles.Inaddition,yellowstarthistlecan causemechanicalinjurytohumans(particularlyto theface)whenthespinesareencountered(Miller 2003). Failuretocontrolyellowstarthistlemayimpose substantial costson neighboringproperties(Jetter etal.2003).Ifarancher,publiclandmanager,or homeowner does not control yellow starthistle, it mayspreadontosurroundingland,whetherrange- land,farmland,roadside,orwildernessarea. Theseimpactsareexploredinmoredetailinthe followingsections. CHA PT ER 2 : Impact Rangelands Althoughnocomprehensiveeconomicassessments havebeenconductedforyellowstarthistle,millions of dollars in losses occur annually from interfer- ence with livestock grazing and forage harvesting procedures,andreducedyieldandforagequalityof rangelands(Callihanetal.1982,RochéandRoché 1988).InastudyconductedattheSierraFoothill Research and Extension Center, it was estimated that a 20-31% infestation of yellow starthistle re- ducedlivestockcarryingcapacitybyabout10-15% (Connor2003).Itwasalsospeculatedthatheavier infestations could reduce the carrying capacity of rangeland by over 50%. Over the entire state of California,itisestimatedthatyellowstarthistlecon- trolexpendituresandlossinforagevalueresultin combinedlossesof6%to7%ofthevalueofpasture (S. Schoenig, California Department of Food and Agriculture,pers.comm.). Cattle, sheep (Ovis), and goats (Capra) will grazeonyellowstarthistleinearlyspringandupto theboltingstage.Becauseofthespinyflowerheads, livestockwillnotgrazeyellowstarthistleonceitbe- gins to mature (Maddox et al. 1985, Sheley et al. 1999a,Thomsenetal.1993,1996a).Thus,yellow Horsewithchewingdisease.Horsespoisonedby yellowstarthistledevelopaneurologicalconditionand mouthulcers.(Photo:J.McHenry) 4 | YELLOWSTARTHISTLEMANAGEMENTGUIDE YSTMgmt(FINAL).indd 4 10/12/06 12:49:25 PM starthistle can greatlyincreasethe cost of manag- ing livestock.Although the nutritional component of yellow starthistle leaves is highly digestible by ruminants during the growing season (Callihan et al.1995),itsnutrientvaluedeclines asthe plants mature.Measuresofproteinandaciddetergentfi- ber (ADF) content indicate that yellow starthistle has acceptable nutritional value as a component ofaruminant’sdiet(Thomsenetal.1989).Inthe boltingtoearlybudstage,proteincontentwas11to 13%andADFwas28to32%.However,ananalysis ofthenutritionalstatusofcattlemanureinthefall indicated that yellow starthistle-infested pastures containconsiderablylesscrudeproteinandtotaldi- gestiblenutrientscomparedtouninfestedpastures (Barry1995)anddonotprovidetherequiredquality offorageinsummerandfall(Connor2003). ToxicitytoHorses Numerousreports havecharacterizedthetoxicef- fect of yellow starthistle on horses (Cheeke and Shull1985,Cordy1978,1954a,b,Kingsbury1964, LarsonandYoung1970,Martinetal.1971,McHenry etal.1990,MettlerandStern1963,Panter1990, 1991,Youngetal.1970).Wheningestedbyhorses, yellowstarthistlecausesaneurologicaldisorderof the brain called nigropallidal encephalomalacia or “chewing disease.” Continued feeding results in brain lesions and mycosal ulcers in the mouth (Kingsbury1964).Thereisnoknowntreatmentfor horsesthathavebeenpoisonedbyyellowstarthistle. Inmostcasestheanimalsdiefromstarvationorde- hydration(Panter1991). Thepoisoningisachronicconditionaffecting the horse primarily after the animal has ingested freshordriedplantmaterialoveranextendedpe- riod, typically a 30 to 60 day period, at cumula- tivefreshweightof60to200%theirbodyweight (Panter 1990, 1991). Cheeke and Shull (1985) reportedthelethaldosetobe2.3to2.6kgyellow starthistleper100kgofbodyweightperday.The clinicalsignsofpoisoningincludedrowsiness,dif- ficultyineatinganddrinking,twitchingofthelips, tongue flicking, and involuntary chewing move- ments. The peak months of poisoning are mid- summer(June-July)andmoreimportantlymid-fall (October-November)(Cordy1954a,b,1978).The summerpeak isassociated withtherapidgrowth phasefollowingspringandthesecondpeakislike- lyduetoautumnrainfallsthatstimulategrowthof plantssurvivingthroughthesummer. Itissuspectedthatrepin,asesquiterpenelactone isolatedfromyellowstarthistle,mayberesponsible forsymptomsinhorses(Akbaretal.1995;Merrill and Stevens 1985). In another study, researchers provided evidencesuggesting that aminoacids as- partateandglutamatemayalsobeinvolved(Royet al.1995). Yellow starthistle poisoning is generally most dangerouswhenitistheonlyfeedavailableorwhen itisasignificantcontaminantofdriedhay.Insome cases, however, horses acquire a taste for yellow starthistleandseek itoutevenwhenother forage is available (Panter 1991). In northern California in 1954, it was estimated that at least 100 cases of horse poisoning by yellow starthistle occurred annually(Cordy1954b).Becausestarthistletoxic- ity isgenerallyrecognized today, veterinarians and researchers note that cases of yellow starthistle poisoning in horses are now relatively uncommon (Segall, UCDavisSchoolof VeterinaryMedicine, pers.comm.). Interestingly, it appears that only horses are affected by ingestion of yellow starthistle. Mules andburrosseemunaffected.However,allgrazing animalscansustaindamagetotheireyesfromthe plant’slong,sharpspines(Carlsonetal.1990). RoadsidesandRecreationalAreas Inadditiontorangeland,pasturesandgrasslands, yellow starthistle is the most important roadside weed problem in much of central and northern California(Anonymous1999,Maddoxetal.1985). YELLOWSTARTHISTLEMANAGEMENTGUIDE | 5 Yellowstarthistlealongroadside.Infestationsspread throughequipmentandvehicles.Roadsideinfestations oftenrepresenttheleadingedgeofspread. YSTMgmt(FINAL).indd 5 10/12/06 12:49:25 PM 6 | YELLOWSTARTHISTLEMANAGEMENTGUIDE Its spread along roadsides probably occurs with themovementofcontaminatedsoil, vehicles and equipment, particularly mowers. These roadside infestationstendtorepresenttheleadingedgeof movementintonewareas,wheretheythenspread into grassland and rangeland habitats (Schoenig 1999). Many recreational areas, including trails and campgrounds,streamsides,huntingareas,andrec- reationalvehicleparksarecontaminatedwithyellow starthistle. Such infestations reduce or eliminate access, resulting in an economic impact on both privateandpublicareas. Wildlands Yellow starthistle infestations may reduce wildlife habitatandforage,displacenative plants,and de- creasenativeplantandanimaldiversity(Sheleyand Larson1994).Denseinfestationsalsothreatennat- uralecosystemsandnaturereservesbyfragmenting sensitiveplantandanimalhabitat(ScottandPratini 1995). Severeinfestationsofyellowstarthistlecanform near-monotypic stands, dramatically impacting plantdiversityintheseareas.InastudyatSugarloaf Ridge study in Sonoma County, California, total plant diversity increased significantly when yellow starthistle was controlled using multiple years of prescribed burning compared to unburned plots (DiTomasoetal.1999a).Thisincreaseindiversity remainedhigherthanuntreatedplotsfortwoyears followingthefinaltreatment(KyserandDiTomaso 2002). HastingsandDiTomaso(1996)suggestthatinva- sionofCaliforniagrasslandsbyyellowstarthistlemay becaused,inpart,byfiresuppressionandreductions infirefrequencyintheseecosystems.AtSugarloaf Ridge,forexample,yellowstarthistleinvadedgrass- lands in the 1980s following 60 years of fire sup- pression.Oncepresent,heavyinfestationsofyellow starthistlemaychangethefireregimebychanging fuelcharacteristicsatagivensite.Thismaykeepthe communityperpetuallyoff-balanceandnotallowthe re-establishmentofnativespecies.Onceestablished asadensestandonasite,yellowstarthistledoesnot provide sufficient fine fuel to carry fire when still green(HastingsandDiTomaso1996).Laterinthe season,driedskeletonsofyellowstarthistlecanpro- videfuelforlate-summerwildfires. WaterConsumption Recent studies indicate that yellow starthistle significantly alters water cycles and depletes soil moisturereservesinannualgrasslandsandfoothill woodlandecosystemsinCalifornia(Benefieldetal. 1998,DiTomasoetal.2000b,2003b,Dudley2000, Enloe2002,EnloeandDiTomaso 2004, Gerlach etal.1998)andinperennialgrasslandsinOregon (Bormanetal.1992).Becauseofitshighwaterus- age,yellowstarthistleincreaseswaterconservation costs and threatens both human economic inter- ests and native plant ecosystems (Dudley 2000). The California Water Resources Control Board hasacknowledgedthatcontrolofweedscouldsig- nificantlyconservewater.Basedonaconservative estimateofstarthistlecoverageintheSacramento River watershed, Gerlach (2004) estimated that yellow starthistle may cause an annual economic loss of $16 to $75 million in water conservation costsalone.Thisamountstoapproximately46,000 acre-feet(15billiongallons)ofwaterlossfromthe Sacramento River watershed each year through transpirationbyyellowstarthistle(Gerlach2004). An estimate for Siskiyou County suggested that thepotentialwaterlosstoyellowstarthistlewould bemorethan26,400,000gallonsofwaterperyear (Enloe2002). Depletionofsoilmoisturebyyellowstarthistle can resultina loss of 15to25% of mean annual Yellowstarthistleinwildlands.Manynaturalareasin Californiaareheavilyinfestedwithyellowstarthistle.At SugarloafRidgeStatePark,grasslandsaredominatedby starthistle.Thisphotoshowsthepotentialofprescribed fireincontrollingstarthistle(backgroundleft,comparedto unburnedforeground). YSTMgmt(FINAL).indd 6 10/12/06 12:49:26 PM [...]... Germinationof yellow starthistle seedshowsacorrelation withrainfallduringtheprecedingtwoweeks(Benefield 2001) Whentheintroductionof newseedsisprevented,the yellow starthistle seedbank declinesalmostcompletelyoverthreeyears(Joley 1992) While yellow starthistle rosettesgrowslowlyduringthewinter,rootsare elongatingrapidly(DiTomaso 2003b) Rootsof yellow starthistle plantsgrow... apositivecorrelationbetweensoildepthand yellow starthistle cover Yellow starthistle seedlingsshowdramaticallyslowerrootgrowth undershadedconditions(DiTomaso 2003b) One hundreddaysaftergermination, yellow starthistle rosettes growninshadeareelongatedcomparedtoplantsgrown infullsun(C.B.Benefield,unpubl.data) Yellow starthistle biomassproductionisstronglycorrelated... tocalote,Sicilian starthistle, and yellow starthistle A yellow starthistle flowerheadgoesthroughpredicablestagesfrombudthroughsenescence.Viableseedset isthecriticalpointforthoseseekingtocontroltheplant.(Photo:J.Clark) Topreventseed production,late-seasoncontroltechniquesshouldbeused whenplantsareintheearlyfloweringstage,asshownhere Beforebolting, yellow starthistle develops... yearsafterburningceased.Theseedbankwasgreatly reducedbutrecoveredquicklyintheabsenceoffollowup management (KyserandDiTomaso2002) Burningforcontrolof yellow starthistle ismostsuccessfulatthebeginningofflowering,when otherplantspeciesaredrybut yellow starthistle seedisnot yetviable A negativecorrelationbetween yellow starthistle coverand coverofperennialgrassindicatesthatthetwoplanttypes... andseparatesshootsfromrootsinyoungplants. < (Photo:G.Kyser) (Photo:G.Kyser) Ifmowedtooearly, yellow starthistle mayrecoverandforma“pincushion”oflow-growing flowerheads Mowing yellow starthistle abovethebasalbranchesdoes notpreventdevelopmentofseedheads(Benefield 1999) Yellow starthistle developsdifferentbranchingpatternsdepending onwhetheritisgrowninopensunoramonggrassesina... Threeyearsofburning atSugarloafRidgeshiftedthecompetitiveadvantagefrom yellow starthistle tofire-adaptednativeplants In thespringafterburningatSugarloafRidgeStateParkto control yellow starthistle, highersoiltemperatureswere measuredcomparedtounburnedsites(DiTomaso 1999a) AtSugarloaf RidgeStatePark, yellow starthistle soilseeddensitywas monitoredduringathree-yearburnprojectandforthree... andseeddispersal, yellow starthistle stemsretain whitecottonytipsinto thewinter Boltingisastageofvigorousshootgrowth duringthetimeofgreatestlightavailability Percentageof yellow starthistle headsthatare floweringcanbeusedbymanagersasanindicatorof seedmaturationinordertotimelate-seasontreatments (Benefield 2001) Thenumberof yellow starthistle seedsinthesoilispositivelycorrelated... shownforcomparison(Benefield 1999) Yellow starthistle rosettesinfull sunlightgrowcompactandflattened(top).Ingrasslands wheretheyreceivelesslight,rosettesdevelopamoreerect growthform(bottom).Theerectformismoresusceptible tomowing Whenusedaspartofanintegrated management program,grazingcanreducethegrowth andspreadof yellow starthistle andothernoxiousweeds.... competedirectly(Enloe2002). ThissiteinSiskiyouCounty,California,was reseededwithwheatgrassaspartofa yellow starthistle controlprogram Aseeddrillattachmentusedforreseeding Wheatgrass,hereshownestablishingalongseeddrillingrows,canbeusedtoout-compete yellow starthistle afterother management methods haveremovedit Alandmanagerusingaseeddrill onrangeland Wheatgrasswasplantedtwo... Atthespinystage,cattleandsheepwillnot graze yellow starthistle, butgoatswillcontinuetobrowseit Table1. omparisonofgrazingcharacteristicsofcattle,sheepandgoats C CaliforniaDepartmentofForestry&Fire ProtectionconductsaprescribedburnatSugarloafRidge StateParkinCalifornia Anincreaseinplantspeciesrichnesswasfoundfollowing threeyearsofburningtocontrol yellow starthistle, SugarloafRidgeStatePark(DiTomaso . .BiologyandEcology Three yellow- floweredCentaureas.Fromlefttoright: tocalote,Sicilian starthistle, and yellow starthistle. 8 | YELLOW STARTHISTLE MANAGEMENT GUIDE YSTMgmt(FINAL).indd 8 10/12/06 12:49:30 PM YELLOW STARTHISTLE MANAGEMENT GUIDE . million acresinCaliforniaby1985(MaddoxandMayfield 1985).Today,itisthoughttohavespreadtoover 15millionacres,andcanbefoundin56ofthe58 countiesinCalifornia(Pitcairnetal.1998b). Fig.2.Soilmoistureunder yellow starthistle com- paredtoannualgrasses.Thevolumetricwatercontent ofsoilunder yellow starthistle isreducedcomparedtosoil underannualgrassesnearUCDavis,July1996(Gerlach 2003). Fig.1.ExpansioninCalifornia.Acomparisonofesti- matedinfestationareainCaliforniashowsarapidexpan- sionoverthelast50years(Pitcairnetal.2006). Distributionof yellow starthistle inwesternstates. Whileplainsstateshavemanygrasslandweedsthatthreat- enCalifornia, yellow starthistle isonegrasslandweed spreadingfromCalifornia.Dataprovidedin2001bystate weedcoordinatorsandcompiledbyEricLane,Colorado WeedCoordinator. 2 | YELLOW STARTHISTLE MANAGEMENT GUIDE YSTMgmt(FINAL).indd 2 10/12/06 12:49:23 PM ofalfalfaseed(Gerlach1997a).Duringthe1920s, yellow starthistle