USDA 

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D 

United States Department of Agriculture 

Field Guide for Managing Annual 

and Biennial Invasive Thistles in 

the Southwest 

Forest Southwestern 

Service Region TP-R3-16-08 Revised June 2017 
 

 

 

 

 

 

Cover Photos 

Top left: Bull thistle — Steve Dewey, Utah State University, Bugwood.org 

Top right: Plumeless thistle flowers — Todd Pfeiffer, Klamath Country Weed Control, Bugwood.org 

Bottom left: Musk thistle flowers — Ricky Layson, Ricky Layson Photography, Bugwood.org 

Bottom right: Scotch thistle — Steve Dewey, Utah State University,Bugwood.org 

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Bull thistle (Cirsium vulgare (Savi)Tenore) 

Musk thistle (Carduus nutans L.) 

Plumeless thistle (Carduus acanthoidesL.) 

Scotch thistle (Onopordum acanthiumL.) 

Sunflower family (Asteraceae) 

Bull, musk, plumeless, and Scotch thistles are annual and 

biennial nonnative plants in the sunflower family that are 

considered invasive. Plumeless and Scotch thistles are 

listed as noxious weeds in both Arizona and New Mexico. 

Musk thistle and bull thistle have been listed as noxious 

weeds only in New Mexico. 

This field guide serves as the U.S. Forest Service’s 

recommendations for management of annual and biennial 

invasive thistles in forests, woodlands, and rangelands 

associated with its Southwestern Region. The 

Southwestern Region covers Arizona and New Mexico, 

which together have 11 national forests. The Region also 

administers 4 national grasslands located in northeastern 

New Mexico, western Oklahoma, and the Texas panhandle. 

Description 

All thistles addressed in this guide are annual to biennial in 

growth form. They reproduce solely by seed and are 

prolific seed producers. The seed remains viable in the soil 

for many years. At maturity, these spiny weeds have basal 

rosettes, purplish disk flowers, and flowering stems that are 

highly branched. Distinguishing features by which 

individual species can be identified include plant size, 

appearance of phyllaries (involucral bracts), and the 

hairiness and shape of the leaves. Growth characteristics 

useful for identifying these thistles are given in table 1. 

Ecology 

Impacts/Threats 

Thistles are highly competitive and persistent plants. Given 

suitable conditions, these weeds rapidly invade rangeland, 

pastures, abandoned fields, roadsides, and disturbed sites. 

A high density of thistles reduces availability of quality 

forage and the diversity of flora and fauna species. 

Additionally, most thistles have taproots that do not 

stabilize the soil as well as fibrous roots of native grass 

species; therefore, high densities of thistles can contribute 

to soil erosion and stream sedimentation. 

Site/Distribution 

Thistles readily establish on disturbed or neglected sites, 

especially along roadsides, railways, ditch banks, and 

waste areas. Bull thistle grows best in nitrogen-rich soil 

with moderate moisture but do not grow as well in sandy 

soil, pure clay, or soils with high organic matter content. 

Musk and plumeless thistles prefer fertile soil overlying 

limestone bedrock while plumeless thistle occupies drier, 

well-drained sites. Scotch thistle prefers sites in dry 

climates with fertile soils and high moisture content. 

Spread 

Thistle seed is easily dispersed by wind, water, birds, and 

other animals. Seed can be dispersed by adhering to 

surfaces and undercarriages of road vehicles and road 

maintenance equipment. Thistles may also be introduced 

via seed in hay that is not certified to be weed free. 

Invasive Features 

Excessive grazing favors thistle over grasses since 

livestock do not prefer to graze these weeds. In spring, 

thistles develop a large rosette base that shades the soil and 

reduces competition from other emerging plants. 

Moreover, some thistles have allelopathic propertiesthat 

slow or prevent growth of desirable plant species, thereby 

allowing these thistles to thrive. 

Management 

Since all thistle species addressed in this guide are prolific 

seed producers, the best approach for controlling these 

species is prevention and proactive management. The 

following actions should be considered when planning a 

management approach: 

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Table 1. Growth characteristics 

Species Life Span Growth and 

Root Habit VegetativeAppearance Flower and Phyllary1 Seed 

Bull thistle Biennial or 

annual 

Rosette up to 3 

feet in diameter. 

Several primary 

roots each with 

many laterals. 

Bushy appearance. 

Leathery, deeply lobed, green 

leaves; prickly hairs on upper 

side; underside wooly; 

yellowish pointed spines. 

Hairy stems with dark purple 

veins; broad, prickly wings 

line stem. 

Purple disk flower. 

Phyllary urn-shaped; 

spiny. 

Glossy light brown to pale 

yellow or white seed with 

narrow, dark brown stripes; 

0.1 to 0.15-inch long. 

Musk Biennial or Rosette up to 2 Waxy, pale green silver- Showy purplish-red disk Straw-colored glossy seed 

thistle winter feet or more in margined leaves with yellow flowers that “nod” at a with stripes, plume-like 

annual diameter. spine tips. 90 degree angle. bristles, and a light apical 

Single, fleshy Multi-branched stems; stem Phyllary with broad, rim; 0.15 to 0.2-inch long. 

taproot 15 to 16 wings do not extend overlapping, brown 

inches long. completely up stem. bracts; resembles a pine 

cone. 

Plumeless Biennial or Rosettes up to 2 Plant looks like a Red to purple disk Small, grey to light brown 

thistle winter feet or more in candelabrum. flowers (smaller than seed with slight curvature 

annual diameter. 

Stout, fleshy 

taproot. 

Deeply lobed leaves with 

white margins and 1 to 3 very 

stiff spines; hairy underside. 

musk thistle). 

Very narrow phyllary 

bracts with short, sharp 

and distinct light apical 

collar; 0.07 to 0.11-inch 

long. 

Flower stems branched with spines. 

spiny wings. 

Scotch 

thistle 

Biennial or 

short-lived 

perennial 

Rosette up to 6 

feet in diameter. 

Stout, fleshy 

taproot up to 12 

inches or more. 

Large, grey-green, coarsely 

lobed, spiny-edged leaves with 

wooly hairs. 

Stems have prominent spiny 

wings. 

Purple disk flowers on 

globe-shaped heads with 

many spiny phyllaries in 

overlapping rows. 

Mottled brown to blackish 

seed with wavy ridges and 

pinkish to red pappus 

bristles that fuse into a ring 

at the base; 0.16 to 0.2-inch 

long. 

1 A phyllary is an involucral bract subtending (located below) the flower head of a composite plant. 

• Maintain healthy plant communities to prevent or 

limit thistle infestations. This may involve 

improving grazing management practices to prevent 

overgrazing. 

• Limit disturbance and/or promptly revegetate 

disturbed areas with desirable perennial forage 

species, especially perennial grasses. 

• Check hay and straw for weed seed before using in 

thistle-free areas. Certified weed-free and pellets 

should be fed to horses used in backcountry areas. 

• Detect, report, record, and eradicate new 

populations of thistle as early as possible. 

• Combine mechanical, cultural, biological, and 

chemical methods for most effective thistle control. 

• Implement monitoring and a follow-up treatment 

plan for missed plants and seedlings. 

• Map extensive infestations. Keep annual records of 

reported infestations. 

Table 2 summarizes some management options for 

controlling thistles under various situations. Further details 

on these options are explained below. Choice of individual 

method(s) for thistle control depends on the extent and 

density of infestation, current land use, and site conditions 

(accessibility, terrain, microclimate, other flora and fauna 

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present, etc.). Other important considerations include 

treatment effectiveness, overall cost, and the period of 

time needed to achieve control. More than one control 

method may be needed for a particular site. 

Special Considerations 

There are at least 20 species of native thistles in the 

genus Cirsium in Arizona and New Mexico. These 

native, non-invasive thistles are important components 

of their ecological communities and should not be 

treated. Since native thistles can be confused with 

invasive thistles, accurate identification of thistle 

species is an important first step in thistle management. 

The Sacramento Mountain range in southern New 

Mexico serves as habitat for the endangered 

Sacramento Mountains thistle (Cirsium vinaceum), 

which is protected under the Endangered Species Act of 

1973. Parts of the Sacramento Mountain range within 

Otero County are also inhabited by local populations of 

Wright’s marsh thistle (C. wrightii), which is a New 

Mexico-listed endangered species and a Federal 

candidate for listing. Wright’s marsh thistle is also 

found in Eddy, Chaves, Guadalupe, and Socorro 

Counties in New Mexico. Both thistle species occur in 

wetland habitats such as spring, seeps, and marshy 

edges of streams and ponds. To avoid harming these 

species, information should be obtained from the U.S. 

Fish and Wildlife Service at (505) 346-2525 before 

treating thistles in these habitat types within the 

Sacramento Mountains and aforementioned counties. 

Physical Control 

Physical methods can be used to control thistles by 

reducing seed production and preventing germination 

through the destruction of individual thistle plants and 

any maturing seed heads. Methods that sever or 

eliminate the entire top of a thistle or its root system 

usually have to be repeated and must be timed properly 

to be effective. 

Manual Methods 

Hand pulling, hoeing, grubbing, or cutting may be done 

any time of year; but these methods are most effective if 

done before flower head development occurs. Thistle 

plants should be severed 2 to 4 inches below the soil 

surface to prevent re-sprouting from the root crown. For 

isolated thistles or small infestations, seed heads of 

individual plants may be clipped and placed in bags for 

disposal. This method can prevent further seed dispersal 

or seedling establishment while also allowing treated 

plants to be more easily relocated next year. 

Proper disposal of debris is essential in preventing 

spread. If flowers or seed are not present, plants may be 

pulled and left onsite. If flowers or seed are present, 

debris should be bagged and removed from the site for 

safe disposal or else piled and burned onsite. 

Mechanical Methods 

If using machinery to manage thistles, the equipment 

should be cleaned after use to prevent movement of 

seed into un-infested areas. 

Tillage – Properly timed and repeated tillage with a 

plow or disc can provide effective control; however, illtimed or nonrecurring tillage may encourage further 

invasion. In areas with high densities of viable thistle 

seed, tillage may actually increase establishment of 

thistle seedlings in succeeding seasons through 

disturbance of the soil surface. If tillage is used, thistle 

plants should be cultivated shortly after they emerge but 

before they reach a height of 3 inches. Shallow 

cultivation in hot, dry weather greatly stresses plants. 

Tillage will not eradicate seeds; therefore, tillage may 

be more effective when combined with other control 

methods. 

Mowing – Mowing reduces plant height of thistles but 

may not entirely eliminate flowering and seed 

production. Some vegetation management experts do 

not recommend mowing at all since plants often 

produce side branches that have more flowers, even 

with repeated mowing and proper timing. However, 

mowing may be useful when combined with other 

control methods (see “Management Strategies” at the 

end of this field guide for more information). If mowing 

is used, cut soon after plants begin to bolt but before 

flowering; repeat mowing about every 21days during 

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Table 2. Management options* 

Site Physical Control Cultural Control Biological Control Chemical Control 

Roadsides Repeat mowing very close to 

surface throughout the growth 

season (preferably in the bolt to 

early bud growth stage before 

seed matures and disperses). 

Consider mowing as part of a 

combined approach. 

Use seed, mulch, and fill 

materials certified to be weedfree. 

Educate road crews to identify 

and report infestations along 

roads; implement 

requirements for vehicle 

operations in infested areas. 

Use biocontrol agents (flies 

and beetle) if release does 

not threaten rare or 

endangered native thistles 

(see table 3). Agents for 

thistle control may be used 

only if thistle infestations are 

large enough to sustain 

control agent populations. 

Apply herbicides in 

spring or fall at 

rosette stage. When 

using truck or tractor 

spraying equipment, 

wash thoroughly 

afterward to prevent 

seed spread. 

Effectiveness of agents may 

be limited due to possible 

disturbances in agent life 

cycles from roadside 

operations. 

Rangelands For smaller infestations, hand 

pull; otherwise, cut plants 2 to 4 

inches below the surface with a 

hoe, grubbing tool, or spade. Cut 

prior to flowering. 

For larger infestations, use welltimed mowing to reduce seed 

production (bolt to flower bud 

Use seed and forage hay 

certified to be weed-free; use 

pellets for horses in 

backcountry areas. 

After passing through infested 

areas, inspect and remove any 

seed from animals, clothing, 

and vehicles before entering 

Use prescribed grazing to 

target young thistles. Closely 

manage grazing to prevent 

overuse. 

Use biocontrol agents (flies 

and beetle) if release does 

not threaten rare or 

endangered native thistles. 

Use individual plant 

treatment with a 

backpack sprayer on 

sparse populations. 

For extensive and 

dense infestations, 

use ground or aerial 

broadcast spraying. 

stage). 

Although prescribed burning is 

not recommended, individual 

plant treatment with a blow torch 

or similar device may be an 

treated or un-infested areas. Agents for thistle control 

may be used only if thistle 

infestations are large enough 

to sustain control agent 

populations. 

option in localized situations. 

Wilderness Same as above Use seed and forage hay Same as above Same as above 

and other certified to be weed-free; use 

natural areas pellets for horses in 

backcountry areas. 

After passing through infested 

areas, inspect and remove any 

seed from animals and 

clothing before entering 

treated or un-infested areas. 

Post signs warning visitors to 

inspect for seeds and remove 

them from animals, clothing, 

and vehicles when leaving an 

infested area. 

* Choice of a particular management option must be in compliance with existing regulations for the land resource 

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active growth. For sites where plants have begun to 

flower, consider walking through the infested area 

before mowing and either pull plants or cut stems that 

have open flowers. Flower heads should be bagged and 

disposed offsite to prevent seed dispersal. 

Prescribed Fire 

Broadcast burning can eliminate existing plants, but this 

activity is likely to favor invasive thistles in future 

years. Thus, prescribed burning is not ordinarily 

recommended for thistle management. However, 

individual plant treatment (IPT) with a blowtorch or 

flamethrower has been used with some success on 

thistles in California. 

Cultural Control 

Early detection and plant removal are critical for 

preventing establishment of thistle. Introduction of 

thistles should be prevented in areas where they are not 

currently present. Land managers, the local public, and 

road crews should be educated on how to identify 

invasive thistle species so they can help report suspected 

infestations. Seed and materials used for mulch, forage, or 

fill should be certified to be weed-free; pellets may be 

used for horses in backcountry areas. 

Biological Control 

Grazing 

Livestock generally avoid entering dense stands of 

mature thistle; but they will graze young, immature 

thistles. Prescribed grazing, therefore, can be effective 

if intensive, short-term grazing is used. Cattle, sheep, 

and goats can be used to graze bull thistle rosettes. 

Musk thistle is readily grazed by sheep and goats from 

rosette to bolting stage and by cattle before the bud 

stage is reached. Goats and cattle graze Scotch thistle in 

the seedling to vegetative stages. Use of grazing in 

combination with herbicide can increase effectiveness 

of both control methods. 

Classical Biological Control 

There are several approved biocontrol agents (flies and 

a beetle) that attack bull, plumeless, and musk thistles 

(see table 3); however, there is no biocontrol agent for 

Scotch thistle. Biocontrol agents are most suitable for 

sites where other control methods are impractical. 

Biocontrol agents for thistles should be used only if 

infestations are large enough to sustain populations of 

these agents. Some biocontrol agents are less effective 

when their life cycle is disturbed, either by the presence 

of livestock or by management actions involving the 

thistle. Treatments such as cutting or spraying may not 

allow the biocontrol agent to complete its life cycle. As 

a result, the needs of the biocontrol agent (if present) 

should be considered before other weed treatments are 

implemented. For further information on biocontrol of 

annual and biennial thistles, see Winston et al. (2008) in 

the “References and Further Information” section of 

this field guide. 

Although biocontrol agents have been released over the 

years for thistle control, many were released before 

testing for host specificity was as advanced as it is now. 

The seed head weevil (Rhinocyllus conicus) has been 

found attacking the endangered Sacramento Mountains 

thistle in southern New Mexico. The rosette weevil 

(Trichosirocalus horridus) has also recently been found 

in the Sacramento Mountains, and its presence could 

impact the Sacramento Mountains thistle along with 

local populations of the Wright’s marsh thistle, which is 

an endangered species listed by New Mexico and a 

Federal candidate for listing. 

Concerns about impacts to non-target species have 

caused APHIS to cancel interstate permits for some 

older thistle biocontrol agents like R. conicus and T. 

horridus. Although these older biocontrol agents may 

be present in thistle populations, they should not be redistributed into new areas. Land managers should 

contact the New Mexico Ecological Services Field 

Office of the U.S. Fish & Wildlife Service at (505) 346-

2525 before releasing any thistle biocontrol agents 

within the Sacramento Mountains or in the counties of 

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Table 3. Biocontrol agents approved for annual and biennial invasive thistles 

Species Type of Agent 

Plant 

Impacted/Site of 

Attack 

Impact on Host Use/Considerations for Release 

Cheilosia 

corydon 

Shoot, stem, and 

root-boring fly 

Bull, musk, and 

plumeless thistles: 

shoots, stems and 

roots 

Larval mining interferes with plant 

function and ultimately results in a 

decrease of seed production and 

sometimes death. 

This insect survives in a wide array of 

climatic conditions throughout the range 

of host thistles. It tends to do better in 

areas where host plants flower early. It is 

available for re-distribution in western 

States, but it is not widespread. 

Urophora 

solstitialis 

Seed head fly Musk and 

plumeless thistles: 

seed heads 

Larval feeding reduces seed 

production in musk and plumeless 

thistles. Galls from larval feeding 

act as metabolic sinks that divert 

resources away from normal plant 

development. 

This insect’s establishment within the 

United States has not been confirmed, so 

it is unavailable for collection. 

Urophora 

stylata 

Gall-forming fly Bull thistle: seed Adult lays eggs in the closed flower 

buds. Each larva forms its own gall 

tissue and the gall forms around the 

immature seed. Mature larvae reside 

in the flower head through winter. 

Pupation is in May, and adults 

emerge in June. 

Species is well established in the western 

U.S. with 60 to 90 percent of bull thistle 

seed heads infested in some areas. 

Psylliodes 

chalcomera 

Leaf beetle Musk and 

plumeless thistles: 

leaves, buds, and 

flowers 

Larval feeding stunts growth and 

reduces seed production of musk 

and plumeless thistles thereby 

decreasing their rate of spread. 

Little is known about habitat preferences 

of P. chalcomera beyond the 

observation that it survives both cold 

and hot temperatures. This species is 

currently not established in North 

America despite repeated introductions. 

Eddy, Chaves, Guadalupe, and Socorro in New Mexico 

that can impact these endangered thistles. Organisms 

(insects, pathogens, etc.) used as biocontrol agents in 

southwestern States should be adaptable to arid 

environments and local conditions. Public, tribal, and 

private land managers may obtain biocontrol agents for 

release directly from local offices of the USDA Animal 

and Plant Health Inspection Service (APHIS) when these 

agents are available. Other sources for biocontrol agents 

include locally developed insectaries or private 

companies. 

A permit must be obtained from APHIS before biocontrol 

agents can be transported across State lines. Regulations 

and permit applications (PPQ 526 permit forms) 

pertaining to interstate shipment of biocontrol agents can 

be found at https://www.aphis.usda.gov/aphis/ourfocus/ 

planthealth/import-information/permits/regulatedorganism-and-soil-permits/sa_apply/ct_plantpest 

_howtoapply. Although biocontrol agents may be 

collected and released internally in a given State without 

an APHIS permit, the State’s department of agriculture or 

agricultural extension service should be consulted for any 

regulations relating to movement of these agents within 

the State. 

Chemical Control 

Thistles are best controlled with a post-emergent broadleaf 

herbicide that is foliar applied. The most commonly used 

herbicides include dicamba, clopyralid, or picloram either 

alone or in combination with 2,4-D. Two relatively new 

herbicides, aminopyralid and aminocylopyrachlor, are 

labeled for thistle control and are also effective. Cost, 

availability, and effectiveness are important in the choice 

of product to use. 

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Table 4. Herbicide recommendations 

Common 

Chemical Name 

(active ingredient) 

Product 

Example1 

Broadcast 

Treatment 

(rate per 

acre) 

Spot Treatment 

(spray solution)2 Time of Application Remarks 

Aminopyralid Milestone bull, musk, 

and plumeless 

thistles: 3–5 

fluid ounces 

Scotch thistle: 5 

to 7 fluid ounces 

3–5% Lower rate for rosette; 

higher rate at bolting. Fall 

or spring. 

Labeled for use on 

wildlife management 

areas and other natural 

areas. May be applied 

up to water’s edge. No 

grazing restrictions. 

Aminopyralid + 

2,4-D3 

GrazonNext bull, musk, and 

plumeless 

thistles: 1.5–2 

pints 

Scotch thistle: 

2–2.6 pints 

3–5% Full leaf through 

flowering. If using in 

combination, wait 9 to 12 

months to spray after last 

mowing. 

Most perennial grasses 

are tolerant of this 

herbicide, as long as 

they are established. 

Aminocyclopyrachlor 

+ chlorsulfuron 

Perspective 3–8 ounces Consult label for 

spot applications. 

Apply to actively growing 

plants. Lower rate for 

rosette in fall; higher rate 

at bolting in spring. 

Selective herbicide used 

on non-crop sites; may 

cause temporary injury 

to some grass species. 

Aminocyclopyrachlor 

+ metsulfuron methyl 

Streamline 4.75–9.5 ounces Same as above. Same as above. Same as above. 

Clopyralid Stinger 

Reclaim 

0.33–1.3 pints 1–3% During active growth at 

rosette stage. 

Established perennial 

grasses are tolerant. 

Clopyralid + 2,4-D3 Curtail 1–2 quarts 1–3% Rosette in spring or fall. Same as above. 

Clopyralid + triclopyr Redeem 1.5–2 pints 1–3% Same as above. Same as above. 

Imazapic Plateau 8–12 ounces 3–5% Same as above. May cause slight 

damage to cool season 

grasses. 

Metsulfuron + 2,4-D3 

+ dicamba 

Cimarron 

Max 

Rate II to III Consult label Same as above. Established perennial 

grasses are tolerant. 

Picloram4 Tordon 22K 0.5–2 pints 1–3% Any growth stage; 

however, application is 

most effective in the fall 

when plants are in rosette 

stage. 

May pose a risk 

to groundwater in 

permeable soils 

or in areas where 

the water table is 

near the surface. 

Picloram4 + 2,4-D3 Grazon P+D bull thistle: 

1–2 pints 

other thistles: 

2–4 pints 

1–2% Lower rate for rosette stage 

in spring or fall; higher rate 

for bolt to bud growth 

stage. 

Established perennial 

grasses are tolerant. 

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Table 4. Herbicide recommendations (cont.) 

Common 

Chemical Name 

(active ingredient) 

Product 

Example1 

Broadcast 

Treatment 

(rate per 

acre) 

Spot Treatment 

(spray solution)2 Time of Application Remarks 

Dicamba + 

diflufenzopyr 

Overdrive 4–6 ounces 1–3% Rosette in spring or fall. Use higher rate for older 

or denser stands. 

Dicamba + 

2,4-D3 

Weedmaster 

(pre-mixed) 

1.5–2 pints 1–2% During active growth; 

lower rate for rosette in 

fall; higher rate in spring 

(not advisable to spray 

during bolt). 

Same as above. 

1 Trade names for products are provided for example purposes only, and other products with the same active ingredient(s) may be available. Individual 

product labels should be examined for specific information and appropriate use with thistles. 

2 Spray solution is the herbicide/water ratio in a spray mix that may be used for spot treatment with backpack or hand-held sprayers. The amount of product 

applied during an annual growing season must not exceed the maximum application rate per acre as specified by the product label – refer to the product 

label for the site type and application. 

3 2,4-D is a restricted-use pesticide in New Mexico only. A certified applicator’s license is required for purchase and use. 

Herbicides listed in table 4 are effective in reducing 

invasive thistles while allowing perennial native grasses 

to compete. Label instructions and guidelines for 

mixing, application, and grazing restrictions following 

treatment should always be followed. Aquatically 

approved herbicide formulations and surfactants must 

be used in or near water. 

Herbicide Application 

For thistles covered in this guide (bull, musk, 

plumeless, and Scotch), the best time for application is 

usually during the fall when new plants have emerged 

and are actively growing during the seedling to rosette 

stage. Spraying in spring through the summer is also 

effective, but higher rates of application may be 

necessary. Consult label directions carefully. 

Herbicides may be applied by backpack or hand-held 

sprayers, ATV or UTV sprayers, or a conventional 

boom sprayer that is pulled or attached to a tractor or 

truck. Any equipment used to apply herbicide should be 

calibrated. For individual plant treatment (IPT), wet the 

foliage and stem thoroughly by using a backpack or 

hand-held sprayer with a single nozzle. These 

herbicides can impact broadleaf and woody species; 

therefore, precautionary measures should be taken if 

desirable non-target species need protection. 

Management Strategies 

High priority for thistle management should be directed 

toward preventing establishment and eliminating new 

plants. Small infestations occurring within otherwise 

healthy sites should be given special priority for control 

treatments. Individual plants in small infestations may 

be controlled by various methods including hand 

pulling, grubbing, hoeing, cutting (stems or seed heads), 

or spot spraying. Destroy debris via fire or mulching (or 

bag and remove plants and/or seed heads). If the treated 

site is disturbed, reseed with desirable perennial grasses. 

Periodically monitor for emerged plants and spot treat 

or hand remove. 

Satellite populations and perimeter edges of large 

infestations should be treated first with the entire 

infestation scheduled to be reduced and/or eradicated in 

a series of steps over a period of several years. Initial 

treatment of well-established infestations should 

attempt to eliminate live thistle plants and disrupt seed 

production as much as possible by using an integrated 

management strategy that involves several control 

methods. 

Since annual and biennial thistles germinate nearly 

year-round, a range of plant sizes may be present at any 

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one site. Consider applying herbicide as the initial 

treatment if thistle seedlings and young rosettes are mostly 

present in fall or early spring. Mowing or using an 

intensive grazing approach on a short-term basis may be a 

better option if treatment is started in late spring or 

summer. When mowing, cut weeds very close to surface 

during the early bud stage before flowers begin to color or 

mature. Mowing will need to be repeated during the 

summer growing season. Herbicide spraying in the fall 

should be considered as a follow-up treatment after 

mowing. Monitor for return of perennial native vegetation 

and reseed with desirable perennial forage species if 

necessary, especially perennial grasses. Repeat over 

multiple years. 

Regardless of the treatment approach, thistles typically 

will not be controlled in a single year or by using only one 

control method. Since it is ordinarily useless to treat an 

area only one time without retreatment, sufficient 

resources must be allocated for the area where control is 

attempted. After initial treatment, it is especially important 

that resources are also available to respray or retreat the 

treated area as necessary. Previously treated areas should 

always be continuously monitored and retreated when 

necessary. Failure to perform follow-up management may 

result in a return of the thistle infestation. 

Adaptive Management 

Invasive thistles are common throughout the western 

United States and controlling these species across broad 

areas is often impractical. Therefore, realistic goals and 

objectives should be established to manage thistle 

infestations occurring extensively throughout a given 

landscape. To improve long-term success, consider using 

an adaptive management approach with the overall goal of 

restoring desirable plant communities. The stepwise 

process for adaptive management involves: 

1. Assessment of the overall weed problem, 

2. Establishing management goals and objectives, 

3. Implementation of control strategies and measures, 

4. Monitoring the effectiveness of management 

actions, 

5. Evaluating actual outcomes in relation to expected 

results, and 

6. Adjusting practices as necessary. 

Steps of this process should be repeated in sequence as part 

of a continuous learning cycle that improves management 

planning and strategy by learning from the outcomes of 

previous management actions. In general, an adaptive 

management strategy is considered to be successful if: 

1. Stakeholders are actively involved and remain 

committed to the process, 

2. Monitoring and assessment are used to adjust and 

improve management decisions, and 

3. Management goals and/or objectives for the 

resource are being achieved. 

References and Further 

Information 

Antognini, J., P.C. Quimby, Jr., C.E. Turner, and J.A. 

Young. 1995. Implementing Effective Noxious 

Range Weed Control on Rangelands. Rangelands. 

17(5):158-163 

Cardina, J., C. Hern, T. Koch, and T. Webster. Ohio 

Perennial and Biennial Weed Guide. Published by 

Ohio State University Extension. Available at http:// 

www.oardc.ohio-state.edu/weedguide/default.asp 

(accessed April 2010) 

Coombs, E.M., et al (eds.) 2004. Biological Control of 

Invasive Plants in the United States. Oregon State 

University Press. Corvallis, Or. 467 pp. 

Davison, J.C., E. Smith, and L.M. Wilson. 2007. Livestock 

Grazing Guidelines for Controlling Noxious Weeds 

in the Western United States. A WesternRegion 

Sustainable Agriculture, Research and Education 

Project. Publication EB-06-05. Available athttp:// 

www.cnr.uidaho.edu/rx-grazing/Livestock_Graizng_ 

Guidelines%28Davison_et_al.%202007%29.pdf 

(accessed May 2010). 

9 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DiTomaso, J.M. and E.A. Healy. 2007. Weeds of 

California and Other Western States. University of 

California Agriculture and Natural Resource 

Publication 3488. p. 235-249. Available at 

http://books.google.com/books (accessed March 

2010). 

Gassmann, A. and L.T. Kok. 2002. Musk Thistle. p. 229– 

245. In R. Van Driesche et al. (eds.) Biological 

Control of Invasive Plants in the Eastern United 

States. USDA Forest Service Publication FHTET2002-04. Available at http://www.invasive.org/ 

eastern/biocontrol/18MuskThistle.html (accessed 

April 2010). 

Invasive Plant Atlas of the United States. Available at 

http://www.invasive.org/weedus/index.html 

(accessed May 2010). 

Kok, L.T. and A. Gassmann. 2002. Bull Thistle (Spear 

Thistle). p. 247-250. In: R. Van Driesche et al. (eds.) 

Biological Control of Invasive Plants in the Eastern 

United States. USDA Forest Serv. Publ. FHTET2002-04. Available at http://www.invasive.org/ 

eastern/biocontrol/pdf/19BullThistle.pdf (accessed 

April 2010). 

Kok, L.T. and A. Gassmann. 2002. Plumeless Thistle 

(Curled Thistle, Bristly Thistle) p. 255–261. In R. 

Van Driesche et al. (eds.) Biological Control of 

Invasive Plants in the Eastern United States. USDA 

Forest Serv. Publ.FHTET-2002-04. Available at 

http://www.invasive.org/eastern/biocontrol/21Plumel 

essThistle.html (accessed April 2010). 

Lym, R.G. and K.M. Christianson. 1986. The Thistles of 

North Dakota. North Dakota StateUniversity 

Extension Service Publication W-1120. Available at 

http://www.ag.ndsu.edu/pubs/plantsci/weeds/w1120/ 

w1120w.htm#Invasive (accessed April2010). 

Lym, R.G. and R. Zollinger. 2000. Perennial and Biennial 

Thistle Control. North Dakota State University 

Extension Service Publication W-799. Availableat 

http://www.ag.ndsu.edu/pubs/plantsci/weeds/ 

w799w.htm (accessed May 2010). 

Randall, J.M. 2000. Bull Thistle (Cirsium vulgare). In C.C. 

Bossard et al. (ed.) Invasive Plants of California’s 

Wildlands. University of California Press. Berkley, 

CA. Available at http://www.cal-ipc.org/ip/ 

management/ipcw/online.php (accessed May 2010). 

Sullivan, P.G. 2004. Thistle Control Alternatives. National 

Sustainable Agriculture Information Service. 

Available at http://attra.ncat.org/attra-pub/PDF/ 

thistlecontrol.pdf (accessed May 2010). 

USDA Plants Database. 2010. Available at 

http://plants.usda.gov/index.html. 

Van Driesche, R., S. Lyon, B. Blossey, M. Hoddle, and R. 

Reardon (eds.) 2002. Biological Control of Invasive 

Plants in the Eastern United States. USDA Forest 

Service FHTET-2002-04. Available athttp://www. 

invasive.org/eastern/biocontrol/ (accessed April 

2010). 

Whitson, T.D., et al. (eds.) Weeds of the West. Western 

Society of Weed Science in cooperation with 

Cooperative Extension Services, University of 

Wyoming. Available at http://plants.usda.gov/java/ 

invasiveOne?pubID=WSWS (accessed March 2010) 

Winston, R., R. Hansen, M. Schwarzländer, E. Coombs, 

C.B. Randall, and R. Lym. 2008. Biology and 

Biological Control of Exotic True Thistles. USDA 

Forest Service FHTET-2007-05. Morgantown, WV. 

Available at http://www.fs.fed.us/foresthealth/ 

technology/pdfs/ExoticTrueThistles.pdf (accessed 

Feb. 2011). 

Suggested Web Sites 

Duncan, K, K. McDaniel, and M. Renz. 2005. Chemical 

Weed and Brush Control for New Mexico 

Rangelands. New Mexico State University College of 

Agriculture and Home Economics and Cooperative 

Extension Service. Las Cruces, NM. 14 pp. Available 

at http://aces.nmsu.edu/pubs/_circulars/CR_597.pdf 

Encycloweedia Datasheets by California Department of 

Food and Agriculture. Available at: 

http://www.cdfa.ca.gov/phpps/ipc/weedinfo/ 

spinythistle-key.htm. 

10 
 

 

 

 

For more information or 

other field guides, contact: 

USDA Forest Service 

Southwestern Region 

Forest Health 

333 Broadway Blvd., SE 

Albuquerque, NM 87102 

Or visit the Southwestern Region’s 

website for invasive species: 

http://www.fs.usda.gov/goto/r3/invasivespecies 

The use of trade or firm names in this publication is for reader 

information only and does not imply endorsement of any 

product or service by the U.S. Department of Agriculture. 

Recommendations made here for 

pesticide use are not obligatory, 

nor do they imply that discussed 

uses have been registered. All 

uses of pesticides must be 

registered by appropriate State 

and/or Federal agencies before 

they can be applied. 

CAUTION: Pesticides can be 

injurious to humans, domestic 

animals, desirable plants, and fish or other wildlife—if they 

are not handled or applied properly. Use all pesticides 

carefully and lawfully. Follow recommended practices for the 

disposal of surplus pesticides and pesticide containers. 

.