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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
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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
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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
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