starthistle can greatly increase the cost of manag-ing livestock.Although the nutritional component of yellow starthistle leaves is highly digestible by ruminants d
Trang 1WeedScienceProgram,DepartmentofPlantSciencesUniversityofCalifornia,Davis
GUYB.KYSER
DepartmentofPlantSciences,UniversityofCalifornia,DavisMICHAELJ.PITCAIRN
BiocontrolProgram,IntegratedPestManagementBranchCaliforniaDepartmentofFoodandAgriculture,Sacramento
Engineer Research and Development Center
Trang 2and 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,
logicalcontrolinsects.DaleWoodsandViolaPopescu,alsowithCDFA’sBiological
DesignedbyMelanieHaageCopyright©2006byCaliforniaInvasivePlantCouncil
Trang 3onyellowstarthistleseedheadinsects...... 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........................62Contents
Trang 5T
hecenteroforiginofyellowstarthistle(Cen-taureasolstitialisL.)isbelievedtobeEurasia,
whereitisnativetoBalkan-AsiaMinor,theMiddle
East, and south-central Europe (Maddox 1981).
Its introduction into NorthAmerica probably
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
lishedasdenselocalpopulationsintheseareasand
fields.Duringthisperiod,yellowstarthistleestab-alongadjacentroadsides.Theuseoftractorsand
other equipment spread starthistle seed to other
locations, including grain fields. Gerlach (1997a)
ablydecreasedbetween1920and1940,mostlikely
Trang 6Introduction 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
weed dynamic of the rangeland system, in which
wildlife and livestock participated in the spread
Trang 7yellow 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
as New York (Maddox et al. 1985). It has also
extended into Canada from British Columbia to
arecoveredwithmicroscopic,stiff,appressed,hair-andfur.Thepappusisnotaneffectivelongdistance
winddispersalmechanismaswinddispersalmoves
seedsonlyafewfeet(Roché1992)
Trang 8Food 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
Research and Extension Center, it was estimated
that a 20-31% infestation of yellow starthistle ducedlivestockcarryingcapacitybyabout10-15%
re-(Connor2003).Itwasalsospeculatedthatheavier
infestations could reduce the carrying capacity of
rangeland by over 50%. Over the entire state of
trolexpendituresandlossinforagevalueresultin
Trang 9starthistle can greatly increase the 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), its nutrient value declines as the plants
mature.Measuresofproteinandaciddetergentfi-ber (ADF) content indicate that yellow starthistle
has acceptable nutritional value as a component
the brain called nigropallidal encephalomalacia
or “chewing disease.” Continued feeding results
in brain lesions and mycosal ulcers in the mouth
tongue flicking, and involuntary chewing
move-ments. The peak months of poisoning are
and Stevens 1985). In another study, researchers
provided evidence suggesting that amino acids
cases, however, horses acquire a taste for yellow
starthistle and seek it out even when other 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 (Cordy 1954b). Because starthistle ity is generally recognized today, veterinarians and
toxic-researchers note that cases of yellow starthistle
poisoning in horses are now relatively uncommon
(Segall, UC Davis School of Veterinary Medicine,
pers.comm.)
Interestingly, it appears that only horses are
affected by ingestion of yellow starthistle. Mules
yellow starthistle is the most important roadside
weed problem in much of central and northern
California(Anonymous1999,Maddoxetal.1985).
Yellowstarthistlealongroadside.Infestationsspread
throughequipmentandvehicles.Roadsideinfestations
oftenrepresenttheleadingedgeofspread.
Trang 10Its spread along roadsides probably occurs with
starthistle. Such infestations reduce or eliminate
access, resulting in an economic impact on both
privateandpublicareas
Wildlands
Yellow starthistle infestations may reduce wildlife
habitat and forage, displace native plants, and
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
Recent studies indicate that yellow starthistle
significantly alters water cycles and depletes soil
hasacknowledgedthatcontrolofweedscouldsig-estimateofstarthistlecoverageintheSacramento
River watershed, Gerlach (2004) estimated that
yellow starthistle may cause an annual economic
loss of $16 to $75 million in water conservation
Trang 11decreasewaterlevelsinstreamsandlakes,reduc-ing water availability for recreational activities.
Decreased stream flows may also reduce or delay
and late-season food source for bees in California
(Edwards 1989, Goltz 1999). In 1959, about
150,000 bee colonies utilized yellow starthistle as
a source of pollen and nectar.At that time honey
from yellow starthistle was valued at $150,000 to
Trang 12ellowstarthistleisawinterannualwidelydis-tributed in the Central Valley and adjacent
foothills of California. It is currently spreading in
Its extended growing and flowering season allows
it to persist within relatively closed grassland
1993). The three yellow-flowered species include
Centaurea solstitialis (yellow starthistle), Centaurea
melitensis (tocalote, Napa or Malta starthistle), and
Thus, a significant amount of cross-fertilization
insures a high degree of genetic variability within
populations
tionofyellowstarthistle,andhavebeenreportedto
Honeybeesplayanimportantroleinthepollina-account for 50% of seed set (Maddox et al. 1996).
Bumblebees are the second most important floral
Trang 13mowing, prescribed burning, and herbicides should
be conducted before approximately 2% of the total
spinyheadshaveinitiatedflowering.
Trang 14nism and most simply fall to the soil just below
1993).Theseseedshavenowinddispersalmecha-the parent plant. With pappus-bearing seed, 1993).Theseseedshavenowinddispersalmecha-the
persalmechanism.Roché(1991a,1992)reported
pappusisnotaneffectivelongdistancewinddis-that92%ofyellowstarthistleseedfallwithintwo
feetoftheparentplant,withamaximumdispersal
distanceof16ftoverbaregroundwithwindgusts
ants, quail, house finches, and goldfinches feed
Trang 16secutiveyearsofburning,withnofurtherseedrecruit-
seedling populations. In many areas, a significant
amount of self-thinning occurs and only a small
fraction of seedlings reach reproductive maturity
Following germination, yellow starthistle allocates
resources initially to root growth, secondarily to
this same time period, rosettes expand slowly. In
a study conducted in Washington by Roché et al.
as subsequent germination often results in
sig-nificant infestations. Consequently, effective
late-season control strategies such as mowing, tillage,
prescribed burning, or postemergence herbicides
should be conducted after seasonal rainfall events
et al. 1989, 1993), most studies in California show
a more rapid rate of depletion. In one study, yellow
Trang 17ampleseedproductionintothedrysummermonths
(Sheleyetal.1993).
The potential density of yellow starthistle in a
particular site can be closely associated with soil
Since yellow starthistle plants germinate over
an extended time period beginning with the first
Trang 18smaller plants, light suppression is a significant
factor regulating root growth. The roots of larger
slowly throughout the early spring. In the Central
Valley and foothills of California, bolting typically
Moreover,thepresenceofspinesonthebractssur-herbivory.Thisisparticularlyimportantduringthe
vulnerablefloweringandseeddevelopmentstages
Senescencetypicallyoccursinfallwhenmoisture
becomes limiting and plants are exposed to frost.
Flowers can abort development before completion.
Senescedstemscancontainthenon-pappus-bearing
seedsforaboutamonthuntilthespinybractsand
phyllaries fall off. Flowerhead receptacles contain
pearance. In contrast, Malta starthistle (tocalote)
finechaffthatgivestheseedheadsacotton-tipap-tip seed heads after senescence. Stems of yellow
in)inheight.Thisuprightformallowsthemtocap-through the senescing grass canopy in late spring
(Rochéetal.1994).
icantlysuppresstheestablishmentofannualgrasses
Trang 19such as eastern California or other western states,
mature plants rarely survive the winter. Whereas
starthistlecansignificantlyreducesoilmoisturere-soilsthreefeetdeepitcanextractsoilmoisturefrom
fissuresinthebedrock(Gerlachetal.1998).
COMPETITIONWITHINTRODUCEDANNUALGRASSES
Shallow versus deep root partitioning between
yellow starthistle and competing vegetation can
greatlyinfluencethesusceptibilityofgrasslandsto
starthistleinvasion(Brownetal.1998).Sincethe
tivelyshallow,thereislittlecompetitionformois-turebetweenyellowstarthistleandannualgrasses
Seasonalmoisturecanalsoinfluencethecompeti-grasses.Underdryspringconditions,earlymaturing
annual grasses have an advantage over late season
annuals, as they utilize the available moisture and
cies,suchasstarthistle(LarsonandSheley1994).In
completetheirlifecyclebeforethelatermaturingspe-contrast,undermoderateorwetconditions,starthistle
hasanadvantagebycontinuingitsgrowthlaterinto
thesummerandfallandproducingmoreseed.
Thus, in grassland systems, yellow starthistle
would be at a competitive advantage 1) in
Trang 20withdeepsoil,and3)inyearswithmoderatetohigh
spring rainfall (Sheley and Larson 1992). Under
these conditions, yellow starthistle would mature
zone (Brown et al. 1998), including many native
perennial grasses. Increased species diversity,
onlycontrollingthenoxiousweed,butalsoimprov-sionbyothernoxiousweedspecies.Toaccomplish
ofthatecosystem,andpreventingreinvasionorinva-mentplan.Developmentofamanagementprogram
thisusuallyrequiresalong-termintegratedmanage-andselectionofthepropertool(s)alsomaydepend
atedvegetation,initialdensityofyellowstarthistle
onotherfactorssuchasweedspeciesandassoci-infestation,effectivenessofthecontroltechniques,
years necessary to achieve control, environmental
considerations, chemical use restrictions, phy, climatic conditions, and relative cost of the
topogra-control techniques. A number of considerations
caninfluencethechoiceofoptions,mostimportant
tivesmayincludeforageproduction,preservationof
managementofyellowstarthistle.Suchsystemsin-agementmaybenecessarytosignificantlyreducea
manage-term program. It is possible that several different
approachandtojudgehowitmaybestfitintoalong-strategiescanprovesuccessfulinagivenlocation.
bility,and,mostimportantly,preventionofnewseed
Successfulprogramsincorporatepersistence,flexi-recruitment (DiTomaso et al. 2000b).Advantages,
disadvantages, risks, timing, and strategic role for
eachcontroloptionarediscussedbelow
Trang 21at the base and, consequently, rarely recover, even
programs where plants are sparsely located in the
grassland system. This usually occurs with a new
Trang 22harrows, knives, and sweeps can be used to
dam-age root systems or to separate shoots from roots
Repeated cultivation can be used in the same
season if rainfall stimulates additional
germina-tion between tillage practices (Thomsen et al.
1996b). This will rapidly deplete the starthistle
sirablespecies.Tobeeffective,thismethodmust
seedbank,butmayalsodepleteseedbanksofde-be conducted before yellow starthistle produces
viableseeds.Tillageisoftenusedoncroplandand
probablyaccountsfortherarityofstarthistleasan
sides.Inwildlandsandrangelands,tillageusually
agriculturalweed.Itisoccasionallyusedonroad-isnotanappropriateoptionforcontrolofyellow
starthistle
RISKS
Tillagemustbe appliedwhenthe surfacesoilis
dry, or fragmented plant segments can re-grow
and possibly magnify the problem. Despite its
effectivenessincontrollingannualweeds,itcan
damage important desirable species, expose the
soil for rapid reinfestation if subsequent rainfall
longthelongevityofyellowstarthistlepropagules
occurs(DiTomasoandGerlach2000a),andpro-tion,itcanaltersoilstructure(e.g.,bycompac-tion),increaseerosion,andcausethelossofsoil
byburyingseedsdeepinthesoilprofile.Itaddi-moisture by exposing subsoil. Heavy equipment
also produces fuel exhausts and raises dust, cluding fine particles<10 microns in diameter
in-(PM10)(DiTomaso1997)
Tillage.Harrowing,akindoftillage,damagestheroots
andseparatesshootsfromrootsinyoungplants.
Trang 23Success with mowing depends on proper
tim-ing and the growth form of the plant. Mowtim-ing is
if conducted too early, will not control starthistle
and may even extend its life cycle. On the other
hand, mowing after plants have produced viable
seed will not substantially reduce the seedbank
consistentlydemonstratedover90%controlofyel-over a three-year period. Benefield et al. (1999)
showed that mowing at the early flowering stage,
beforeviableseedproduction,wasmosteffective
incontrollingyellowstarthistle.
These researchers also demonstrated that the
success of mowing as a control strategy depends
partly on the plant’s growth form and branching
pattern. Yellow starthistle plants growing among
other plants in grassland tend to have an erect,
high-branching growth form and are effectively
ing stage. Plants grown in the open tend to have
controlledbyasinglemowingattheearlyflower-trolled well even with repeated mowing at the
Trang 24This occurred during a yellow starthistle control
mow at Fort Hunter Liggett (A. Hazebrook, Fort
Mowing may also decrease the reproductive
efforts of insect biocontrol agents. For example,
ingstage—whichismosteffective—maycausesig-nificantdamagetoseed-feedingbiocontrolagents
Trang 25 The specific goal of livestock (cattle, goats or
sheep) grazing for weed control is to manipulate
the pattern of defoliation so that the target weed
is at a competitive disadvantage relative to other
however,beavaluabletoolinanintegratedmanage-ECONOMICS
One advantage over other methods for the control
of yellow starthistle is that grazing animals can
inproperhealth,andmonitoringtheirgrazingactiv-require the use of a herder or penning animals at
ing,andsometimessupplementalfeeding,especially
night.Otherexpensescanincludestockdogs,fenc-lateintheseasonwhenthenutritivevalueofyellow
starthistle is low (Frost and Launchbaugh 2003).
Without this supplemental feed, production losses
isnotcompletelygrazedandrecoveryoccursrap- Asanaddedbenefitofshortdurationintensive
Trang 26grazeiswhenplantsaremostsusceptibletodefo-is minimal. Thomsen et al. (1989, 1990, 1993)
sive grazing by cattle or goats resulted in reduced
showedthatproperlytimed(MayandJune)inten-
grazing,theremainingforagereduceslightpenetra-
tiontothesoilsurfaceandcansuppressweedes-tablishment and growth. In contrast, conventional
grazing practices allow animals to forage grasses
and other plants nearly to the soil surface.Yellow
starthistlehasbeenshowntobeverysusceptibleto
light suppression (Roché et al. 1994). Shading
re-duces seedling survival rates. Weber (1985) noted
thatRochédelayedspringgrazingofwheatgrassand
was able to control starthistle because ungrazed,
taller wheatgrass plants blocked sunlight from the
starthistlerosettes.
Intensivetime-controlledgrazingcanalsomini-
mizethegrazers’abilitytoavoidlesspalatablenox-ious weed species. High stocking rates may force
cattle to graze typically less preferable species,
including yellow starthistle. This should result in
scale is limited. It has been estimated that 1900
head of cattle would be needed to properly treat
Timingalsocanbecriticaltothesuccessofgraz-ingforyellowstarthistlecontrol.Theidealtimeto Spinystage.Atthespinystage,cattleandsheepwillnot grazeyellowstarthistle,butgoatswillcontinuetobrowseit.
Trang 27when confined and may even strip the bark off
tivespecies.
trees.Livestockcanalsotrampledesirablesensi-PrescribedBurning
Fire has been an important factor in the ment and continuance of most grassland systems.
develop-As a result, many native grassland plants appear
adapted to periodic disturbance by fire. The hard
bolting stage could provide palatable high protein
forage (8 to 14%). This can be particularly useful
inlatespringandearlysummerwhenotherannual
specieshavesenesced.
Selectingthepropergrazingspeciesisimportant
to successful management. In the case of yellow
starthistle, cattle, sheep and goats have all been
Trang 28havefireadaptationssuchashardseedsandearly
maturation,prescribedburninghasbeenshownto
favor germination and establishment of many
spe-cies, particularly legumes (Kyser and DiTomaso
By shifting the competitive advantage to
fire-adapted species, prescribed burning in California
grasslandscanincreaseplantdiversityaswellascon-trolnoxiousweeds.Inthefirstgrowingseasonafter
theburn,plantdiversityandspeciesrichnessoften
increase(HastingsandDiTomaso1996,DiTomaso
et al. 1999a). Two or more years of burning have
resulted in both a reduction in yellow starthistle
an increase in subsequent fall and winter
germi-nation of yellow starthistle seed still in the
seed-bank. In many cases, this enhanced germination
Trang 29 In deciding whether to use prescribed
burn-ing in management, it may be helpful to refer to
Thegoalofasuccessfulburnprogramforyel-low starthistle is to reduce or, in time, eliminate
the soil seedbank. At the end of a consecutive
three-year burn regime in Sugarloaf Ridge State
Park in Sonoma County, the yellow starthistle
early to mid-summer (late June to early July in
most areas of California), which may not be
fea-sibleinsomeareas.Atthistimestarthistleisinthe
veryearlyfloweringstage(similartoidealmowing
timing) and will not have produced viable seeds,
whereas seeds of most desirable species will readyhavedispersedandgrasseswillhavedriedto
al-provideadequatefuel.
Insomecases,yellowstarthistleseedlingshave
ing” techniques, in which heat is applied to wet
Trang 30yellow starthistle-dominated grassland. (It should
be noted that adjacent areas remained infested,
and DiTomaso 2002). A follow-up management
program is essential to the long-term control of
starthistle has proven inconsistent. When spring
drought follows a flaming treatment, control of
starthistle can be excellent (Rusmore 1995). In
In a study by Kyser and DiTomaso (2002) at
Sugarloaf Ridge State Park, a site burned three
consecutiveyears(1993-1995)wasmonitoredfor
an additional four years (1996-1999). Following
the cessation of the burn program, the grassland
degraded rapidly as the competitive advantage
shiftedawayfromfire-adaptedforbs.Thesespecies,
particularlynativelegumes,graduallydeclined,as
didtotalspeciesrichness.Withinthreeyearsthe
burned grassland was not significantly different
from the unburned area, with the exception that
yellow starthistle population levels remained
1996
1997
1996 1997
1996 1997 1998
unburned 3 yr
1995
1995 1995
Bars represent standard error
-1 -2 -3 -4 -5
Trang 31is the impact fire may have on small animals and
insects unable to escape the burn. For example,
species included Festuca idahoensis, Poa secunda,
Festuca kingii, Pseudoroegneria spicata, Leymus nereus,Elymuselymoides,Achnatherumhymenoides,
ci-Hesperostipa comata, and Achnatherum occidentalis
There are a number of risks associated with
pre-scribed burning as a method of controlling yellow
starthistle and other invasive plants. For one, air
quality issues and requirements, including PM10
emissions,canbeasignificantproblemwhenburns
are conducted adjacent to urban areas (Campbell
and Cahill 1996). This potential problem can be
potential of fire escapes. This is particularly true
when burns are conducted during the summer
with later flowering times will be selected against.
In some areas, burning can lead to rapid invasion
by other undesirable species with wind-dispersed
seeds, particularly members of the sunflower
Trang 32is more vigorous than the invasive weed. Only a
limited number of species have proven to be gressive enough to displace invasive species, and
states.Summerrainfallcanbecriticaltotheestab-In Siskiyou County, where the summer weather
pattern is more similar to the Great Basin states,
average rainfall between May and September is
around 4 inches. In contrast, the Sacramento and
San Joaquin valleys average 0.75 inches or less of
precipitationduringthatsametimeperiod
ECONOMICS
Theprimarylimitationtotheuseofnativespecies
in revegetation programs is their high cost. Few
producers are available and the demand for seed
Reseedingrangeland.Alandmanagerusingaseeddrill
onrangeland.
Twoyearsafterreseeding.Wheatgrasswasplantedtwo
yearsagoonthissiteinSiskiyouCounty
Trang 33 Perennial grasses are the most successful in
competing with rangeland weeds. For the long
term, however, it is best to use a combination of
program may fail. In contrast, a spring reseeding
may not survive under conditions of low spring
grasses and/or legumes into existing communities,
or by drill seeding into plowed, disked,
Trang 34 Revegetation programs for yellow starthistle
control generally rely on reseeding with native
speciesorperennialgrasses(Callihanetal.1986,
Johnson1988,JonesandDiTomaso2003,Larson
and McInnis 1989a, Lass and Callihan 1995a,
Northam and Callihan 1988a, b, c, 1990a, b,
Prather et al. 1988, Prather and Callihan 1989a,
b, 1990, 1991). These programs try to eliminate
not only starthistle, but also the invasive annual
grasses that create an ecosystem susceptible to
starthistle invasion. Revegetation with desirable
and competitive plant species can be the best
long-term sustainable method of suppressing
weeds,whileprovidinghighforageproduction.In
western states other than California, competitive
grasses used in revegetation programs for yellow
starthistlemanagementincludecrestedwheatgrass
(Agropyron desertorum), intermediate wheatgrass
(Elytrigia intermedia [=Agropyron intermedium,
Thinopyrumintermedium]),thickspikewheatgrass
(Agropyron dasystachyum), big bluegrass (Poa
am-pla), Bozoisky Russian wildrye (Psathyrostachys
Ideally, competitive, endemic, native
spe-cies should be re-established. The native
for their competitive effect on yellow starthistle.
Thomsen et al. (1996a, 1997) found that
subter-ranean clover varieties were somewhat tiveagainstyellowstarthistlewhencombinedwith
Introducingcompetitivespeciesintoinfestednon-Preferably, competitive, endemic, native species
shouldbere-established.Forexample,nativewil-lows (Salix spp.) and cottonwoods (Populus spp.)
eas.However,inmostcases,particularlyrangeland
havebeenusedtoreplacesaltcedarinriparianar-environments, endemic native species do not pearcapableofoutcompetingnoxiousweeds.
ap- ieshaveusedmorecompetitivenon-nativespecies.
Inyellowstarthistle-infestedareas,manystud-Although non-native, these species provide good
land maintenance. A potential concern is that,
livestockforageandasustainableoptionforrange-onceestablished,manyofthesespecies,especially
cultures.Thiscanhaveadramaticimpactontotal
theperennialgrasses,candevelopintonearmono-dition,itisimportanttoensurethatanintroduced
plantandanimaldiversitywithinthesesites.Inad-specieswillnotitselfbecomeinvasiveandspread
fromtheplantedareaintowildlands.Forexample,
Harding grass (Phalaris aquatica) is a perennial
Trang 35bunchgrass native to the Mediterranean region
Unfortunately, few studies have been conducted
on the restoration of yellow starthistle-infested
Trang 36(biological control agents) to control a target
weed. The objective is to establish self-sustaining
have a competitive advantage over our native
spe-cies, which have their own specialized herbivores
anddiseases.
Use of biological control to manage a noxious
weed differs from other methods in that
manage-mentmeasuresarenotdirectedatparticularpatches
or infestations. Biological control agents are living
organisms and land managers cannot accurately
most damaging and widespread weeds. In the
de-velopment of weed biological control, scientists
examine the target weed in its area of origin and
Invasive Weed Research Unit in Albany and the
California Department of Food and Agriculture
(CDFA) Biological Control Program are actively
pursuing several biological control agents for use
against yellow starthistle in California and the
Budweevil.Bangasternusorientalisisoneofmany
biocontrolagentsreleasedinCaliforniatocontrolyellow
starthistle.(Photo:B.Villegas)
Trang 37Species CommonName Distribution Impact References
Larinuscurtus flowerweevil Limited Low FornasariandTurner1992
Pitcairnetal.1999b
McCaffreyandWilson1994
Pitcairnetal.2000c,2004 Rosenthaletal.1991
Turner1992 TurnerandFornasari1992 Wood1993
Trang 38western United States. Six insect species and a
rust disease have been introduced against yellow
enough to substantially reduce seed production.
The sixth insect, Urophora jaculata, failed to
Trang 39surveys of commercial safflower crops and native
Cirsium thistles showed the fly to be fairly host
specific to yellow starthistle (Villegas et al. 1999,
Sclerotinia minor, Colletotrichum gloeosporioides
and a new species of Ascophyta (Woods 1996,
WoodsandFogle1998,Pitcairnetal.2000b).All
three species are naturally present in California.
Seedlings of yellow starthistle were observed to
looked at the effect of several pathogenic fungi
on yellow starthistle rosettes. The species
evalu-atedincludedFusariumoxysporumf.sp.carthami,
Verticillium dahliae, Phytophthora spp., Botrytis
cinerea, and S. sclerotiorum. Starthistle plants
developed symptoms following innoculation and,