USDA 

-

a 

United States Department ofAgriculture 

Field Guide for Managing

Canada Thistle in the Southwest 

Forest Southwestern 

Service Region TP-R3-16-14 Revised June 2017 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cover Photos 

Top left: U.S. Forest Service 

Top right: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org 

Lower left: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org 

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Canada thistle (Cirsium arvense (L.) Scop., synonym: Carduus arvensis L.)

Sunflower family (Asteraceae) 

Canada thistle is an invasive plant that is listed as a noxious 

weed in both Arizona and New Mexico. This field guide 

serves as the U.S. Forest Service’s recommendations for 

management of Canada thistle 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 Texaspanhandle. 

Description 

Canada thistle (synonyms: creeping thistle, Californian 

thistle, corn thistle) is a patch-forming, creeping perennial 

with prickly, alternate, green leaves that are lance shaped 

and deeply lobed. Male and female flowers occur on 

separate plants (dioecious) but are quite similar in 

appearance. Canada thistle has an extensive, fast growing, 

fibrous root system of lateral and vertical roots that extend 

out 15 feet wide and 15 feet deep. New shoots emerge from 

the root system in spring, but other flushes may also occur 

in fall or during the growing season with favorable soil 

moisture. Canada thistle reproduces from seed and by 

vegetative cloning via adventitious root buds. Seedlings 

grow slowly and are sensitive to competition, particularly if 

shaded. 

Growth Characteristics 

• Patch-forming, creeping perennial; erect, branched,

slightly hairy stem with ridges, 18 to 48 inches tall.

Stems not winged.

• Extensive root system includes taproot and rhizomes.

• Weak rosette base; may have few, if any leaves.

• Alternate, lance-shaped leaves with spiny-toothed

margins; upper surface waxy; sparsely wooly lower

surface.

• Urn-shaped flower heads; spineless, scale-like bracts.

• Pink or purple disk flowers in umbrella-shaped

clusters; male and female flowers are on separate

plants (species is dioecious).

• Reproduces via root buds, rhizomes, and seed. Seed

may remain viable in soil up to 20 years.

• Allelopathic chemicals may inhibit other plants.

Ecology 

Impacts/Threats 

Canada thistle is a highly competitive, persistent plant that 

grows in dense, impenetrable colonies. A highdensity of 

spiny-leafed Canada thistle reduces the availability of 

quality forage and the diversity of flora and fauna species. 

Site/Distribution 

As compared to other thistles, Canada thistle has a more 

limited range and more specific requirements for soil and 

precipitation. It prefers areas with 16 to 30 inches of 

precipitation that have moist, but not waterlogged soils 

such as meadows and hay fields. Found on rangeland and 

disturbed or neglected sites; especially along roadsides, 

railways, ditch banks, and waste areas. 

Spread 

New shoots and roots emerge from almost anywhere along 

the root system, and new plants can develop from small 

broken pieces after disturbance by tillage. Canada thistle 

develops seed sparingly; however, the seeds are winged 

and are easily dispersed by wind, water, birds, and other 

animals. Seed can be spread over wide distances when it 

adheres to the surfaces and undercarriages of road vehicles 

and farm equipment or when introduced into new areas in 

hay that is not certified to be weed free. 

Invasive Features 

Canada thistle produces new shoots from roots each spring, 

but shoots can also develop throughout summer and fall. 

This is a particular problem when plants are stimulated or 

disturbed by mowing, tillage, or fire. 

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Management 

Canada thistle is quite difficult to control once established. 

Prevention, early detection, and eradication are the best 

management tools for controlling this noxious weed. Since 

Canada thistle allocates most of its reproductive energy 

into vegetative reproduction, this attribute can be 

manipulated to the land manager’s advantage through the 

use of various control methods. 

The following actions should be considered when planning 

a management approach: 

• Maintain healthy plant communities to prevent or

limit Canada thistle infestations.

• Check hay and straw for presence of weed seed

before using them in thistle-free areas. Certified

weed-free hay or pellets should be fed to horses used

in backcountry areas.

• Limit disturbance and/or promptly revegetate

disturbed areas with desirable perennial forage

species, especially perennial grasses.

• Detect, report, and eradicate new populations of

thistle as early as possible.

• Combine mechanical, cultural, biological, and

chemical methods for most effective control.

• Implement monitoring and a follow-up treatment

plan for missed plants and seedlings.

• Map known infestations. Keep annual records of

reported infestations.

Table 1 summarizes some management options for 

controlling Canada thistle under various situations. Further 

details on these management options are explained below. 

Choice of individual control method(s) for Canada thistle 

depends on the extent and density of the infestation, 

current land use, and site conditions (accessibility, terrain, 

microclimate, other flora and fauna present, etc.). Other 

important considerations include treatment effectiveness, 

overall cost, and the number of years 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 non-invasive 

native 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 SacramentoMountains 

thistle (Cirsium vinaceum) which is protected under the 

Endangered Species Act of 1973. Portions of the 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 springs, seeps, and marshy edges of streams and ponds. 

To avoid harm to these species, information should be 

obtained from the U.S. Fish and Wildlife Service at (505) 

346-2525 before implementing thistle treatment in

potential habitat for the two species within the Sacramento

Mountains and the aforementioned counties.

Physical Control 

Physical methods to control Canada thistle should focus on 

reducing seed production and destroying the root system. 

These methods usually have to be repeated and must be 

timed properly to be most effective. 

Manual Methods 

Hand-pulling, digging, and hoeing can be done any time of 

year; however, re-sprouting and the need to repeat these 

treatments should be anticipated. Given the perennial 

nature of this weed, hand removal is difficult and typically 

not very effective. 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 or else burned since seed will continue to mature 

within flower heads left onsite. 

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Table 1. Management options* 

Site Physical Control Cultural Control Biological Control Chemical Control 

Roadsides Use repeat 

cultivation or 

mowing (every 7 to 

21 days) to deplete 

stored energy in 

roots; repeated hand 

pulling or hoeing of 

small infestations in 

loose soils will also 

stress root energy 

reserves. 

Use seed, mulch, and fill 

materials certified to be weedfree. 

Train road crews to identify 

and report infestations 

along roads; implement 

requirements for vehicle 

operations. 

Consider using biocontrol agents 

(weevil or gall-forming fly) if release 

does not threaten rare or endangered 

native thistles. Biocontrol agents can 

only be used when thistle 

infestations are large enough to 

sustain control agent populations. 

Effectiveness of agents may be 

limited due to potential disturbance 

of the agent’s life cycle from road 

operations. 

Apply in spring or fall. Use 

truck spraying equipment. 

Wash under vehicle after 

application to prevent 

spread. 

Rangelands Mow at early bolt Use seed and forage hay Use grazing animals on young For extensive and dense 

and hay stage and then again certified to be weed-free; use thistles as part of short-term, infestations in disturbed 

meadows every 21 days during pellets for horses in intensive grazing approach in the areas with few desirable 

growth season. backcountry areas. spring. Closely manage grazing to plant species present, use 

Consider combining 

with herbicide 

treatment. 

After passing through 

infested areas, inspect and 

remove any seed from 

prevent overuse. 

Consider using biocontrol agents 

(weevil or gall-forming fly) if release 

ground or aerial broadcast 

spraying. 

Consider using individual 

Use repeated tillage animals, clothing, and does not threaten rare or endangered plant treatment (IPT) with 

at 20-day intervals vehicles before entering native thistles. Biocontrol agents can a backpack sprayer for 

starting as soon as treated or un-infested areas. only be used when thistle sparse infestations, areas 

plants emerge in late 

winter. Reseed, fertilize, and 

irrigate (if possible) to 

make desirable plants more 

infestations are large enough to 

sustain control agent populations. 

interspersed with desirable 

native plants, or areas 

difficult to access. 

competitive. 

Wilderness 

and other 

natural areas 

Use repeated hand 

cutting or hoeing 

prior to seed set. 

Same as above. 

Post signs warning visitors 

to inspect for seeds and 

remove them from animals, 

clothing, and vehicles when 

leaving an infested area. 

Same as above. Use backpack or handheld sprayers. Broadcast 

spraying by aerial or 

ground methods may be 

used on thicker stands if 

allowed. 

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

Mechanical Methods 

If using machinery to manage Canada thistle, the 

equipment should be cleaned after use to prevent 

movement of seeds into un-infested areas. 

Tillage – Properly timed and repeated tillage with a 

plow or disc can provide limited control. However, illtimed or nonrecurring tillage may favor further spread 

and invasion. Plants should be cultivated after plants 

have emerged in late winter but before they reach a 

height of 3 inches. Cultivation should be repeated at 20-

day intervals until first frost or when plants are 

dormant. Shallow cultivation during hot, dry weather 

greatly stresses plants. Tillage will exhaust carbohydrate 

reserves stored in roots but will not eradicate seeds. 

Therefore, tillage may be more effective when 

combined with herbicide application. 

Mowing – Mowing will reduce plant height but does 

not usually eliminate flower or seed production 

completely. Mow when plants begin to bolt and repeat 

as necessary to prevent seed production. Many 

vegetation management experts do not recommend 

mowing as a single control method as plants often 

produce side branches with more flowers, even with 

repeated mowing and proper timing. Mowing is more 

effective when combined with herbicide treatment. 

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Prescribed Fire 

Burning will not destroy the root system of Canada thistle, 

and thistle presence is likely to increase in succeeding 

years after a fire. Therefore, using prescribed fire as a 

control method is not recommended for managing this 

weed except to remove dead litter and debris. 

Cultural Control 

Early detection and plant removal are critical for 

controlling Canada thistle. Land managers, road crews and 

the local public should be educated on identification of 

non-native noxious species so they can help report all 

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. Vehicles, 

humans, and livestock should be discouraged from 

traveling through infested areas; and a program to check 

and remove seeds from vehicles and livestock should be 

implemented to help stop dispersal. Treated areas may be 

reseeded, fertilized, and irrigated (if possible) to make 

desirable plants more competitive. 

Biological Control 

Grazing 

Livestock generally avoid entering dense stands of mature 

Canada thistle. However, prescribed grazing can be part of 

an effective control strategy by using a short-term, 

intensive grazing approach in spring before the plant 

begins to bolt. Canada thistle seedlings and rosettes are 

grazed most effectively by goats, followed by sheep, and 

then cattle. It is also grazed by horses, donkeys, and llamas 

to varying degrees. Use of grazing in combination with 

herbicide can increase effectiveness of both of these control 

methods. 

Classical Biological Control 

Although a number of classical biocontrol agents are 

available for controlling other invasive thistles, only a gall 

fly (Urophora cardui) and a stem-mining weevil 

(Hadroplontus litura) are available to attack Canada thistle 

(table 2). However, recent studies have not demonstrated 

that U. cardui and H. litura have a significant impact on 

Canada thistle populations. 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 Eddy, Chaves, Guadalupe, and 

Socorro Counties in New Mexico that can impact rare or 

endangered thistles. 

Control with biocontrol agents is most suitable for sites 

where mowing, cultivating, or treating with herbicide is 

impractical. Biocontrol agents for thistles should be used 

only if infestations are large enough to sustain populations 

of these species. 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 thistles, see 

Winston et al. (2008) in the “References and Further 

Information” section of this field guide. 

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/regulated-organism-and-soilpermits/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. 

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Table 2. Biocontrol agents approved for Canada thistle 

Species Type of 

Agent Site of Attack Impact Use/Considerations for Release 

Hadroplontus Stem Adults feed Larval and adult feeding usually This insect species does well in moist, 

litura (formerly weevil on leaves and does not significantly impact disturbed areas where Canada thistle is dense 

Ceutorhynchus stems; larvae populations of Canada thistle and not stressed by drought, grazing, or other 

litura) mine leaf 

veins, stems, 

and root 

crowns. 

directly, though some stunting 

and stand reduction has been 

observed in eastern Oregon. 

Feeding does cause secondary 

damage as pathogens and other 

organisms enter the stems of 

Canada thistle via holes made by 

exiting larvae 

control methods. 

H. litura is readily available for collection in

many states.

Urophora Stem gall Larvae mine Larval feeding forms galls that This fly does well in moist, open and partially 

cardui fly stems. act as metabolic sinks, diverting 

resources away from normal 

plant development. Attacked 

plants produce fewer seeds, are 

less competitive, and may be 

more susceptible to pathogens 

and other insects. 

shaded areas where Canada thistle is scattered. 

Areas subject to disturbance or other means of 

control (grazing, mowing, chemical treatment, 

etc.) are not suitable for this fly’s survival. 

Chemical Control 

Canada thistle is best controlled with a selective postemergent broadleaf herbicide (see table 3). Typically, the 

primary herbicide entry into the plant is through the leaves 

and stems although certain herbicides have excellent root 

uptake properties. Control results can vary due to weather 

and the plant’s growth stage so special careshould be taken 

to follow label directions closely for spraying. 

Effective herbicides for Canada thistle control include 

aminopyralid, aminocyclopyrachlor, clopyralid, and 

picloram mixed alone or in combination with 2,4–D or 

another herbicide. Each herbicide product will have 

different requirements and restrictions according to the 

herbicide label. Aquatically approved herbicide 

formulations and surfactants must be used in or near water. 

Read and understand the label prior to any application. 

Consult the registrant if you have questions or need further 

detail. 

Herbicide Application 

Spraying in fall before Canada thistle enters dormancy 

(before soil freezes up) usually gives the most consistent 

results. Spraying in spring in pre-bud to early bud growth 

stages is also effective, especially with herbicides that are 

mixed in combination with 2,4–D. Use a labelrecommended surfactant in the spray mixture (0.25 to 0.5 

percent v/v; equivalent to 1 to 2 quarts of surfactant per 

100 gals. of spray solution). Follow guidelines in the label 

for mixing instructions. Always follow application 

requirements and grazing restrictions after treatment. 

Herbicides may be applied by backpack or hand-held 

sprayers, ATV or UTV sprayers, or conventional boom 

sprayers that are pulled or attached to a tractor or truck. 

Any equipment used to spray herbicide should be 

calibrated. For individual plant treatment (IPT), wet 

foliage and stems thoroughly using a hand-held or 

backpack sprayer fitted with a cone-shaped adjustable 

nozzle. Herbicides listed in table 3 will impact other 

broadleaf and woody species; therefore, measures should 

be taken if desirable non-target species need protection. 

Integrated Control Methods 

Regardless of the control method used, the key to 

controlling established stands of Canada thistle 

successfully is to stress and eliminate root reserves. The 

following combinations of control methods will reduce 

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root reserves and should be considered for managing Canada 

thistle: 

• Herbicide–regrow–herbicide – This sequence of

control methods can be initiated in either fall or spring.

If started in spring, apply a recommended herbicide

when Canada thistle is less than 15 inches tall and is in

the pre-bud to early bud growth stages. If started or

retreated in the fall, spray during rosette stage with

either aminopyralid (5 to 7 ounces per acre), dicamba

(2 quarts per acre), clopyralid (0.67 pint per acre), or

picloram (1 quart per acre). Treated areas should be

closely monitored for 2 years and resprayed if

necessary. Herbicide combinations with 2,4–D are

more effective in spring than when applied in fall.

• Mow–regrow–herbicide – Mow early in spring and

then repeat 2 to 4 times during growing season. In fall,

allow shoots to regrow to more than 15 inches in

height and then spray with herbicide. Clopyralid (0.67

pint per acre) and picloram (1 quart per acre) are

particularly effective against Canada thistle during this

time since nutrients are being translocated toward the

root system. Consider reseeding with a variety of

desirable perennial forage species following treatment.

Periodically monitor for new seedlings and spot treat

or hand remove regrowth.

• Grazing–herbicide – Use an intensive, controlled

grazing approach on infested areas in spring before

Canada thistle bolts. Fencing may be necessary to

confine livestock to areas of infestation. After

removing livestock, apply herbicide treatment to

Canada thistle before flowering stage. Repeat in fall

with another herbicide treatment if necessary. Monitor

native species, especially grasses. Consider reseeding

with desirable perennial grasses if native grasses do

not naturally recover following control efforts.

Management Strategies 

Strategies to contain and reduce Canada thistle require 

long-term planning and integrated management. A high 

priority for Canada thistle management should be early 

detection and preventing establishment. Small localized 

infestations found on otherwise healthy sites should be 

given first priority for control treatment(s). For large 

infestations, satellite populations and perimeter edges 

should be treated first with the denser core of the entire 

infestation scheduled to be reduced and/or eradicated in a 

series of steps over a period of several years. Initial 

treatment(s) should try to eliminate live plants and disrupt 

seed production as much as possible. 

Large infestations of Canada thistle are especially difficult 

to eradicate; therefore, do not anticipate that they will be 

controlled within a single year or by using only one 

method. Complete control of Canada thistle will likely 

require 2 to 4 years of repetitive treatment. 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 

important that resources are also available to respray or 

retreat the treated area successfully. Previously treated 

areas should always be continuously monitored to detect 

recovering Canadian thistle. Follow-up treatment should 

be anticipated and planned as part of a complete 

restoration program. Failure to perform follow-up 

monitoring and adapt control methods as needed could 

result in recolonization by Canada thistle. 

References and Further 

Information 

Alberta Invasive Plant Council. Invasive Alien Species 

Factsheet: Canada Thistle. Available at http://www. 

invasiveplants.ab.ca/Downloads/FS-CanadaThistle. 

pdf (accessed April 2010) 

Antognini, J., P.C. Quimby, Jr., C.dE. Turner, and J.dA. 

Young. 1995. Implementing Effective Noxious 

Range Weed Control on Rangelands. Rangelands 

17(5):158- 163 

Bayer, D. 2000. Canada Thistle (Cirsium arvense). 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). 

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Table 3. 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 5–7 ounces 3–5% Use lower rate in fall, 

right after flowering 

but before dormancy. 

Use higher rate in 

spring for pre-bud to 

early bud stages. 

Labeled for use on wildlife 

habitat management areas 

and natural areas. May be 

applied up to water’s edge. 

No grazing restrictions. 

Aminocyclopyrachlor 

+ chlorsulfuron 

Perspective 4.75–8 ounces 

Use a high 

quality adjuvant 

4.75–11 ounces 

per 100 gal of 

water. Consult 

label for spot 

applications. 

Apply to actively 

growing plants in 

rosette stage in fall; 

use 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 

Transline 

0.67–1.3 pints 1–3% Rosette to bud stage. Will control top growth and 

inhibit regrowth. Established 

perennial grasses are 

tolerant. 

Clopyralid + 2,4-D3 Curtail 6 pints 1–3% Early bud growth stage 

or in fall at rosette. 

Same as above. 

Clopyralid + triclopyr Redeem 2.5-4 pints 1–3 % Early bud growth stage 

or in fall at rosette 

growth stage. 

Same as above. 

Picloram4 Tordon 22K 1 quart 1–3% Any growth stage; 

however, it is most 

effective in fall just 

after bloom. 

Persistent, selective 

herbicide; may pose a risk to 

groundwater in permeable 

soils or in areas where the 

water table is near the 

surface. 

Dicamba Clarity 

Banvel 

[several 

manufacturers] 

2–3 quarts 1–3% After bloom and 

before dormancy in 

fall. 

Use higher rate for older or 

denser stands. 

2,4-D3 [several 

manufacturers] 

2 quarts (based 

on 1 quart of a 

4 pounds per 

gallon 

concentration) 

5–10% In spring when thistle 

is 10 to 15 inches tall; 

pre-bud to early bud 

stage. 

Less expensive but also less 

effective when used alone. 

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 Canada thistle. 

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. 

4 Restricted-use pesticide – A certified applicator’s license is required for purchase and use. 

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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). 

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

Livestock Grazing Guidelines for Controlling 

Noxious Weeds in the Western United States. A 

Western Region Sustainable Agriculture, Research 

and Education Project. Publication EB-06-05. 

Available athttp:// www.cnr.uidaho.edu/rxgrazing/Livestock_Graizng_Guidelines%28Daviso 

n _et_al.%202007%29.pdf (accessed May 2010). 

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

California and Other Western States. University of 

California Agriculture and Natural Resource 

Publication 3488. pp. 235–249. Available at 

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

2010). 

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

Chemical Weed and Brush Control for New 

Mexico Rangelands. Las Cruces: New Mexico 

State University College of Agriculture and Home 

Economics and Cooperative Extension Service. 

pp. 14. Available at http://aces.nmsu.edu/pubs/ 

_circulars/ CR_597.pdf 

Great Basin and Invasive Weeds. Canada Thistle 

(Cirsium arvense). Available at 

http://www.usu.edu/weeds/plant_species/ 

weedspecies/canadathis.html (accessed April 

2010). 

Invasive Plant Atlas of the United States. Available at 

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

(accessed May 2010). 

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

of North Dakota. North Dakota StateUniversity 

Extension Service Publ. W-1120. Available at 

http://www.ag.ndsu.edu/pubs/plantsci/weeds/w112 

0/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). 

McClay, A.S. 2002. Canada Thistle. Pp. 217–228 In R. 

Van Driesche et al. (ed.) 2002. Biological Control 

of Invasive Plants in the Eastern United States. 

USDA Forest Service Publication FHTET-2002-

04. Available at http://www.invasive.org/eastern/ 

biocontrol/pdf/17CanadaThistle.pdf (accessed 

April 2010). 

Smith, L.L. 2005. DCNR Invasive Exotic Plant Tutorial 

for Natural Lands Managers: Canada Thistle 

Factsheet. Available at http://www.dcnr.state.pa.us 

/forestry/invasivetutorial/canada_thistle.htm 

(accessed May 2010). 

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

National Sustainable Agriculture Information 

Service.Available at http://attra.ncat.org/attrapub/PDF/thistlecontrol.pdf (accessed May 2010). 

Thunhorst, G. and J.M. Swearingen. 2009. Least 

Wanted:Canada Thistle Fact Sheet. Plant 

Conservation Alliance. Available at 

http://www.nps.gov/plants/alien/fact/ciar1.htm 

(accessed April 2010). 

Van Driesche, R. et al. (coords.) 2002. Biological 

Control of Invasive Plants in the Eastern United 

States. USDA Forest Service FHTET-2002-04. 

Available at http://www.invasive.org/eastern/ 

biocontrol/ (accessed April 2010) 

Whitson, T.D. et al. (ed.) 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 in 

March 2010). 

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

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

Biological Control of Exotic True Thistles. Forest 

Health Technology Enterprise Team. FHTET-2007-

05. Morgantown, WV. Available at 

http://www.fs.fed.us/foresthealth/technology/ 

pdfs/ExoticTrueThistles.pdf (accessed Feb. 2011). 

Suggested Web Sites 

Encycloweedia Datasheets by California Department of 

Food and Agriculture. Available at: http://www. 

cdfa.ca.gov/phpps/IPC/weedinfo/cirsium.htm 

For information on invasive species: 

http://www.invasivespeciesinfo.gov/ 

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

For information about calibrating spray equipment: NMSU 

Cooperative Extension Service Guide A-613, Sprayer 

Calibration. Available at http://aces.nmsu.edu/pubs/ 

_a/A-613.pdf 

Herbicide labels online: http://www.cdms.net/ 

9 
 

 

 

 

 

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 recommend practices for the disposal of 

surplus pesticides and pesticide containers.