Cirsium arvense - (L.) Scop.
Creeping Thistle
Other English Common Names: Californian Thistle, Canada Thistle
Other Common Names: Canada thistle
Taxonomic Status: Accepted
Related ITIS Name(s): Cirsium arvense (L.) Scop. (TSN 36335)
French Common Names: chardon des champs
Unique Identifier: ELEMENT_GLOBAL.2.154063
Element Code: PDAST2E090
Informal Taxonomy: Plants, Vascular - Flowering Plants - Aster Family
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Asterales Asteraceae Cirsium
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Concept Reference
Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Cirsium arvense
Conservation Status

NatureServe Status

Global Status: G5
Global Status Last Reviewed: 21Jun2016
Global Status Last Changed: 21Jun2016
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Reasons: Cirsium arvense is one of the most economically important agricultural weeds in the world. It was introduced to North America in the 1600s and soon was recognized as a problem weed. Weed control legislation against the species was passed by the Vermont legislature in 1795 (R. J. Moore 1975). Canada Thistle is now listed as a noxious weed in most areas where it occurs. It has very high seed production, and the runner roots readily survive the fragmentation that accompanies cultivation (FNA vol. 19, 2006).
Nation: United States
National Status: NNA
Nation: Canada
National Status: NNA (07Sep2016)

U.S. & Canada State/Province Status
United States Alaska (SNA), Arizona (SNA), Arkansas (SNA), California (SNA), Colorado (SNA), Connecticut (SNA), Delaware (SNA), District of Columbia (SNA), Idaho (SNA), Illinois (SNA), Indiana (SNA), Iowa (SNA), Kansas (SNA), Kentucky (SNA), Maine (SNA), Maryland (SNA), Massachusetts (SNR), Michigan (SNA), Minnesota (SNA), Missouri (SNA), Montana (SNA), Nebraska (SNA), Nevada (SNA), New Hampshire (SNA), New Jersey (SNA), New Mexico (SNA), New York (SNA), North Carolina (SNA), North Dakota (SNR), Ohio (SNA), Oregon (SNA), Pennsylvania (SNA), Rhode Island (SNA), South Dakota (SNA), Tennessee (SNA), Utah (SNA), Vermont (SNA), Virginia (SNA), Washington (SNA), West Virginia (SNA), Wisconsin (SNA), Wyoming (SNA)
Canada Alberta (SNA), British Columbia (SNA), Labrador (SNA), Manitoba (SNA), New Brunswick (SNA), Newfoundland Island (SNA), Northwest Territories (SNA), Nova Scotia (SNA), Ontario (SNA), Prince Edward Island (SNA), Quebec (SNA), Saskatchewan (SNA), Yukon Territory (SNA)

Other Statuses

NatureServe Global Conservation Status Factors

Range Extent Comments: Despite its common name, Cirsium arvense is native to Eurasia and was apparently introduced to North America during the colonial period. By 1918, it was already on the noxious weed lists of 25 northern states. It is now widespread in all states and Canadian provinces north of 37 degrees N and south of 58-59 degrees N. Infestations are particularly troublesome in the northwest and northcentral states, and in the eastern provinces of Canada (Moore 1975).

Other NatureServe Conservation Status Information

Global Range: Despite its common name, Cirsium arvense is native to Eurasia and was apparently introduced to North America during the colonial period. By 1918, it was already on the noxious weed lists of 25 northern states. It is now widespread in all states and Canadian provinces north of 37 degrees N and south of 58-59 degrees N. Infestations are particularly troublesome in the northwest and northcentral states, and in the eastern provinces of Canada (Moore 1975).

U.S. States and Canadian Provinces
Color legend for Distribution Map
NOTE: The distribution shown may be incomplete, particularly for some rapidly spreading exotic species.

U.S. & Canada State/Province Distribution
United States AKexotic, ARexotic, AZexotic, CAexotic, COexotic, CTexotic, DCexotic, DEexotic, IAexotic, IDexotic, ILexotic, INexotic, KSexotic, KYexotic, MA, MDexotic, MEexotic, MIexotic, MNexotic, MOexotic, MTexotic, NCexotic, NDexotic, NEexotic, NHexotic, NJexotic, NMexotic, NVexotic, NYexotic, OHexotic, ORexotic, PAexotic, RIexotic, SDexotic, TNexotic, UTexotic, VAexotic, VTexotic, WAexotic, WIexotic, WVexotic, WYexotic
Canada ABexotic, BCexotic, LBexotic, MBexotic, NBexotic, NFexotic, NSexotic, NTexotic, ONexotic, PEexotic, QCexotic, SKexotic, YTexotic

Range Map
No map available.

U.S. Distribution by County Help
State County Name (FIPS Code)
NV Carson City (32510), Douglas (32005), Elko (32007), Eureka (32011), Humboldt (32013), Lander (32015), Lyon (32019), Storey (32029), Washoe (32031), White Pine (32033)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
16 Hamlin-Snake Valleys (16020301)+, Southern Great Salt Lake Desert (16020306)+, Pilot-Thousand Springs (16020307)+, Upper Humboldt (16040101)+, North Fork Humboldt (16040102)+, South Fork Humboldt (16040103)+, Pine (16040104)+, Middle Humboldt (16040105)+, Reese (16040107)+, Little Humboldt (16040109)+, Upper Quinn (16040201)+, Lake Tahoe (16050101)+, Truckee (16050102)+, Granite Springs Valley (16050104)+, Upper Carson (16050201)+, East Walker (16050301)+, West Walker (16050302)+, Little Smoky-Newark Valleys (16060006)+, Long-Ruby Valleys (16060007)+, Spring-Steptoe Valleys (16060008)+
17 Salmon Falls (17040213)+
18 Honey-Eagle Lakes (18080003)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: Cirsium arvense is a perennial thistle up to 1.5 meters tall. It is distinguished by its creeping horizontal lateral roots, which produce dense patches of aerial shoots.
Technical Description: The sessile, pinnatifed and prickly leaves are dark green, sometimes wooly beneath (Fernald 1950, Gleason 1957, Moore and Frankton 1974). Plants are imperfectly dioecious. The numerous heads of purple to white flowers (in forma albiflorum) are 1 to 2.5 cm long and one-third to one-fourth as wide. The corolla of the globose male heads is projecting, 12-14 mm long with anthers to 4 mm long. Male flowers occasionally have functional female parts and set seed (Hodgson 1968, Kay 1985, Hayden 1934). Pistillate heads are oblong, with corollas 23-26 mm long, the conspicuous pappus about 14 mm long in fresh flowers.
Diagnostic Characteristics: Thistles of the genus Cirsium are distinguished by their plumose pappus from members of the genus Carduus which are known as "plumeless thistles" because of their simple pappus. Within the genus Cirsium, C. arvense is the most often confused with the bull thistle, C. vulgare. The two species can be distinguished by the larger head and isolated distribution of the bull thistle (Hansen 1918). Gray's Manual of Botany (Fernald 1950) distinguishes C. arvense from all other thistles by its habit of arising from sprouts of a widely creeping root system and its almost universally dioecious plants.
Ecology Comments: The most outstanding biological characteristic of Cirsium arvense is its well developed lateral root system, which sends up new shoots at 6 to 12 cm intervals (Moore 1975). Morphological studies indicate that this is a true root system, developed at depths beyond those used by rhizomes (Friesen 1968). Lateral root growth can exceed 6 m in one growing season (Rogers 1928, Hayden 1934). The depth of vertical roots appears to be determined by the depth of the water table and has been reported to be as deep as 6.75 m (Rogers 1928). The roots are brittle and regeneration has been observed from cuttings as small as 10 mm long and 1 mm in diameter under laboratory conditions (Hamdoun 1972). Root segments 3 cm thick and 6 cm long can regenerate shoots in as short an interval as 5 days (Sagar and Rawson 1964).

Root bud elongation increases with increasing root temperature and photoperiod and is greatest at shoot temperatures of 25 degrees C daytime/15 degrees C night, with a 15-hour photoperiod and 30 degrees C root temperature (McAllister and Haderlie 1985). Under laboratory conditions root buds are inhibited by internal competition for a limiting N supply (McIntyre and Hunter 1975).

Phenology of Cirsium arvense varies with different ecotypes, but follows a general pattern. In Washington State, overwintering roots develop new underground roots and shoots in January and begin to elongate in February (Rogers 1928). Shoots emerge in May, when mean weekly temperatures reach 5 degrees C. Rosette formation follows, with a period of most active vertical growth (about 3cm/day) in mid-to-late June. Flowering in Montana and South Dakota is from early June to August and in Canada from June to September (Hodgson 1968, Van Bruggan 1976, Moore 1975).

Root carbohydrate reserves exhibit an annual cycle. Minimum reserves occur in early June, just before flowering. As growth declines in July, these reserves begin to rebuild and increase in the early fall (Hodgson 1968, Bakker 1960, Arny 1932, Welton et al. 1929).

Cirsium arvense is a long-day plant. Flowering of different ecotypes has been observed under daylengths of 14 to 18 hours, but not under light of 8 to 12 hours (Linck and Kommedal 1958, Hunter and Smith 1972).

Because of the species' dioecious plants and its prolific vegetative reproduction, whole patches of C. arvense are usually one sex or the other. Cross-pollination success is a function of distance. Hodgson (1964) reports that a high proportion of seeds are produced when parent plants are 17 m apart. Seed production decreases with distance between 33 m and 200 m (Hayden 1934) and only a small percentage of seeds are produced from plants 390 m apart (Amor and Harris 1974).

One plant can produce up to 5,200 seeds with an average annual production of 1,530 seeds per plant (Hay 1937) with between 83 and 90 seeds per head (Derschied and Schultz 1960, Hayden 1934). Seed size varies among different ecotypes, ranging from 298,000 to 677,000 seeds per pound (Hodgson 1968). Seeds are known to be dispersed by wind (Bakker 1960) and by run-off in drainage or irrigation ditches (Wilson 1979, Hope 1927).

A succession of seedlings is produced from a single crop of seeds. In a Montana study that compared several western ecotypes Hodgson (1964) found that germination of fresh seed varies with ecotype. Rate of germination ranges between 50 and 95% (Hayden 1934, Hodgson 1964). Under natural conditions, seeds of some Canadian plants germinate immediately, produce rosettes before winter, and emerge to flower the next spring, whereas germination of others is delayed until the following year (Moore 1975). About 90% of all seeds germinate within one year of dispersal (Roberts and Chancellor 1979). Seeds buried as part of Duval's long-term buried seed experiment germinated after 21 years, but peak germination occurred during the third year (Toole and Brown 1946).

Seedling establishment requires high light intensity. Growth is reduced in light of 60-70% full daylight and death ensues when light intensity falls to below 20% of full daylight (Bakker 1960). Under optimum conditions seedlings begin to develop roots capable of vegetative reproduction at 8 weeks (Bakker 1960). Detmers (1927) observed a 101 cm root with 10 shoot buds on a 4-month seedling. Rogers (1928) states that a root fragment more than 6 weeks old can regenerate an entire plant.

Habitat Comments: The northern limit of the zone of highest density in Canada corresponds with the 18 degrees mean January isotherm, whereas the southern limit of the species is probably controlled by high summer temperatures and short-day length (Moore 1975).

Cirsium arvense is found in open, mesophytic areas, with optimal growth corresponding to between 50 and 75 cm annual rainfall (Hodgson 1968). It occurs on all but waterlogged, poorly-aerated soils (Rogers 1928, Bakker 1960, Hodgson 1968, Moore 1975) and in nearly every community within its range where sufficient light is available. Bakker (1960) found an average density of 39 shoots per meter with 41 flower heads per shoot in open sites, and a density of 11 shoots per meter with 18 flower heads per shoot in shaded areas. Patches are most prevalent in disturbed areas such as agricultural land, roadsides, ditch spoil banks, gopher mounds and overgrazed pastures (Moore 1975).

C. arvense apparently has difficulty becoming established from seed in undisturbed areas. Amor and Harris (1974) report no seedling establishment from seed artificially sown in pastures, whereas 7 to 13% of seeds sown on bare dirt emerged and 78 to 93% of these became established. In spring wheat fields, Canada thistle increased in abundance by 192% over a four-year period, whereas over the same interval it declined to 1% of its previous value in alfalfa fields mowed twice yearly for hay (Hodgson 1968).

Economic Attributes Not yet assessed
Management Summary
Stewardship Overview: Integrated control options for natural areas managers are constrained by the need to restrict damage to native species. Although it appears that burning in June (Jaeger pers. comm.) or later (Smith 1985) is more effective for thistle control that early burning, this practice is also more harmful to native species.

It appears that the best available option for control of thistle in native prairies is to strengthen the component of native species by spring burning and follow-up by cutting or spot application of glyphosate on Canada thistle in late bud or early bloom.

Species Impacts: Cirsium arvense competes with crops for moisture, nutrients, and light. It is responsible for millions of dollars of direct crop loss annually, with additional costs for control (Hodgson 1968, Messersmith 1978, Wilson 1980). Its spiny nature and patchy growth render infested pastures unusable to livestock. It interferes with the harvest of horticultural crops (Boldt 1981). It harbors destructive insects and pathogens (Linck and Kommedal 1958) and has been reported to have an allelopathic effect on sugar beet, wheat, alfalfa, corn, edible beans, and flax (Wilson 1981, Helgeson and Konzak 1950). Studies in Colorado indicate that species diversity in an "undisturbed" study area was inversely proportional to the relative frequency of Canada thistle (Stachion and Zimdahl 1980).

Within the context of natural areas, Canada thistle is more often a legal and public relations issue than a biological threat. However, in the west it can invade areas that are subject to heavy deer and elk grazing and areas newly exposed as a result of control of another weed, the tansy ragwort (MacDonald pers. comm.). In the Midwest it can invade established prairie where a mixture of blown-in snow and dirt leaves annual accumulations of new soil surface (Heitlinger pers. comm.), where surface runoff results in accumulation of litter, where erosion creates newly exposed soil surfaces (Winter pers. comm.), and where mist application of nonselective herbicides has set back succession (Jaeger pers. comm.).

Management Requirements: Much of the need for management of Cirsium arvense in natural areas arises from the need to respond to noxious weed laws. See THREATS section.

Methods of thistle control in the literature focus on the management of thistle in agricultural systems. Cultural, mechanical, chemical and biological methods have been developed for thistle eradication.

MOWING: Early studies recommend mowing at frequent intervals. Hansen (1918) recommends mowing twice a year to prevent seed set. Detmers' (1929) recognized the need not only to prevent seed set, but to starve the root system and therefore recommended weekly mowing. Following studies that demonstrated that root carbohydrates reach an ebb in June (Welton et al. 1929, Arny 1932) efforts were made to time mowing to deplete root reserves. Systematic monthly mowing for a four-year period eliminated practically all the thistles (Welton et al. 1929). The greater the number of mowings the greater the effectiveness of control. Repeated mowing at 21-day intervals weakens roots and prevents seed production (Seely 1952), but is more labor-intensive that most farmers and managers can afford. Hodgson (1968) found that mowing alfalfa fields twice annually, at early-bud to preflowering stage (early to mid-June in Montana) and early fall (September) reduces thistle to 1% of its initial value in four years. A single mowing at early-bud stage accomplishes top removal when root carbohydrate reserves are minimal (Hodgson 1968).

Observations at Red Rock Prairie, Minnesota, during the 1987 season, suggest that more than a single mowing or handcutting is needed to keep thistles from forming flowers on side branches after cutting. As many as 5 repeated cuts were necessary on individual thistles at this site from June to September to prevent blooming. (Sather pers. obs.)

It appears that if labor is limited, the strategy of a single mowing at early bud stage would be most effective. The short delay until early flower stage (when natural area managers often cut because plants are most easily seen) will probably not result in significant carbohydrate build-up.

None of the older literature substantiates the suggestion by Minnesota farmers (Heitlinger pers. comm., 1987; Winter pers. comm., 1987) that cutting thistles during a wet spell will kill them by causing the roots to rot. Hansen (1918) does not mention cutting, but states that plowing, harrowing and cultivation will be less effective in wet weather.

GRAZING: Early authors suggest grazing as a method of control. Although livestock are not attracted to thistle, sheep will graze and trample plants that have been treated with salt (Detmers 1927, Cox 1913). Rogers (1928) states that very young plants will be eaten by goats or sheep in the spring, but that grazing is the least effective control method for Cirsium arvense. There are no available data on the effect of stocking rates or grazing intensities. It seems likely that animal disturbance from conventional grazing would encourage the spread of C. arvense, as has been demonstrated for C. lanceolatum, C. vulgare, and C. undulatum (Tomarek and Albertson 1953, Ankle 1963, Hetzer and McGregor 1951).

SMOTHER CROPS: Rogers (1928) discusses the principle of smother crops as the effect of choking out an undesirable species by shading. Smother crops must come up earlier than C. arvense and grow rapidly during the early summer in order to shade out the thistle. They must be able to hold their own against the growing thistle and retain their vigor until frost (Rogers 1928). Although these principles were meant to apply in the selection of smother crops on cultivated fields or haylands, they might be applicable in the selection of native "smother" species of use in restoration of disturbed patches in managed areas.

Alfalfa and sweet clover are both effective smother crops. Alfalfa is favored over the taller sweet clover because it is cut earlier and more often, producing the side-effect of depleting thistle root carbohydrates. Detmers (1927) recommends sowing at rates of 11.2 to 16.8 kg/ha for thistle control. Other plants that have been used as smother crops include grasses, millet, sugar beets, sorghum, hemp, buckwheat, and small grains (Cox 1913, Rogers 1928). Although the terminology is no longer used, smother crops continue to be used in integrated pest management systems for C. arvense (Hodgson 1968).

BURNING: No studies have been designed specifically for the purpose of assessing burning as a method of thistle control. However, in studies comparing the response of warm season grassland in eastern Kansas to May and June burns, Alson (1975) found that although thistle abundance was initially increased by May burns, within two growing seasons it declined below the level in control areas. Immediate reductions in thistle abundance were found following June burns. In the same study, May burns in cool season grassland produced immediate reduction of thistles in comparison to a control (Olson 1975).

Summer burning in North Dakota appears to reduce thistle infestations even on bare soils. Thistle seed production is heavy throughout the summer in areas burned in June. In areas first burned in July or August late summer crops of thistle seedlings are large, but the plants freeze prior to flowering (Smith 1985).

CHEMICAL CONTROL: The major problem in using herbicides for control of C. arvense is the plant's deep, well-developed root system. Most herbicides that would be used to control broad-leaved perennials do not translocate easily into the root system (Baradari et al. 1980, Marriage 1981). Methods of increasing translocation are therefore at the forefront of research dealing with chemical control of deep-rooted perennials. The literature is enormous and response varies between ecotypes and varieties (Hodgson 1968, Saidak 1966).

Several environmental factors and methods of application enhance the effectiveness of herbicides. Effectiveness of phenoxy herbicides (MCPA and 2,4-D) is greatest when root carbohydrate reserves are low (Marriage 1981).

Translocation of glyphosate is significantly greater in plants at the bud to flowering stage than in younger plants (Sprankle et al. 1975). Laboratory studies indicate that total plant absorption of glyphosate and dicamba decreases with increasing water stress, translocation of glyphosate to root buds declines with increasing water stress, but picloram metabolism is unaffected (Lauridson et al. 1980).

Lisk and Messersmith (1979) have found greater translocation of glyphosate plus 2,4-D below the treated area when herbicide is applied to stems rather than leaves. Translocation to roots was greater when herbicide was applied to the upper leaf surface than to the lower.

Increased translocation of some herbicides can be caused by growth regulators. Baradari et al. (1980) found that leaf absorption of dicamba was increased from 32% to 64% and basipetal translocation was increased from 6% to 9% by simultaneous application of chlorflurenol. However, similar responses were not observed in studies of ethephon and chlorflurenol with glyphosate (Tworkoski and Sterret 1985). A combination of herbicide with fertilization has also proven effective under some circumstances. Hodgson (1968) found combination treatments with 2,4-D at .24 to 2.24 kg/ha with 33.6 kg/ha nitrogen and 112 kg/ha phosphorus resulted in better thistle control and higher yields of spring wheat than either herbicide or fertilizer alone.

Jaeger (pers. comm., 1987) states that boom spray application of 2,4-D for thistle control in Kilen Woods State Park, Minnesota, was ineffective because it set back the succession of natural communities, actually opening areas for thistle invasion. Application of Roundup to individual plants with a Walk-a-Wick applicator was difficult because the thistles were often below grass level. In 1985, park personnel converted to the use of a Solo backpack tank of 4 to 5 gallon capacity with the nozzle modified by a brass adjustment to apply a straight stream (not mist) at low pressure. Roundup at 3-4% is mixed with a purple agricultural dye and herbicide is dribbled at the top of the stem, dribbling downward. Both the time involved and amount of herbicide are cut in half by use of the dye, which persists as a marker of treated plants for up to a week. Plants are treated in the pre-bud stage and rounds are made weekly to assure treatment of plants that may have been missed in the initial application.

BIOLOGICAL CONTROL: Although over 80 native species of insects plus over 50 other native species ranging from fungi to birds are known to frequent Cirsium arvense, only four are presently considered as important enemies of the plant (Maw 1976). These species are the beetles Cassia rubiginosa Muell., Coleoptera, Chrysomelidae and Cleonus piger Scop., Coleoptera, Cuculionidae; a fly, Arellia ruficauda Fab., Diptera, Tephritidae; and the painted lady butterfly, Vanessa Cardui L., Lepidoptera, Nymphaidae (Evans 1984). Only Orellia ruficauda appears to do damage (Maw 1976, Forsyth and Watson 1985), and the level of damage is probably not sufficient to act as a control.

Rust species of the genus Puccinia offer greater possibilities as biological control agents. Although damage is probably not sufficient for the rust alone to control thistle populations (Ososki et al. 1979, Turner et al. 1980) preliminary results in England suggest that Puccinia punctiformis can be used in conjunction with 2,4-D in integrated programs of thistle control (Haggar et al. 1986).

Four European insects- Ceutorhynchus litura, Urophora cardui, Altica carduorum, and Lema cyanella- have been released for Canada thistle control in North America with some promise of success.

Since its initial introduction in North America in 1967, the cuculionid beetle Ceutorhynchus litura has become established in five provinces and in Montana (Peschken and Wilkinson 1981, Story et al. 1985). Weevil populations have increased at nine release sites in Canada (Peschken and Wilkinson 1981). Although C. litura is not effective as a sole means of control, it weakens and damages the plants by mining the stems (Peschken and Wilkinson 1981).

The gall fly Urophora cardui reduces shoot size and vigor of infested thistles (Peschken and Harris 1975) inhibits seed production (Laing 1978), and results in lower root and above-ground weights than gall-free plants (Peschken and Harris 1975). Since its release in 1974, U. cardui has become established in eastern Canada, but not in western Canada where dry summers may be the limiting factor (Rotheray 1986).

The Chrysomelid beetle Altica carduorum weakens C. arvense by defoliation and feeding on flower heads. It was first regarded as a promising control agent because of its specificity and continuous feeding habit, but has proven unsatisfactory because of its susceptibility to predation (Peschken et al. 1970, Story et al. 1985, Schaber et al. 1975).

A second Chrysomelid, Lema cyanella has been released in Canada, but will not be released in the United States because its host preference includes some native California thistles (Turner pers. comm. 1987).

INTEGRATED CONTROL: In agricultural systems, integrated pest management programs appear to provide more effective thistle control than any individual method. Integrated systems combine the use of herbicides, cultivation and smother crops.

In Ontario there appeared to be a synergistic relationship between infestation of thistle by C. litura and infection by the rust Puccinia punctiformis. 87% of rust-infected thistles were mined by weevils compared with 32% of uninfected shoots (Peschken and Beecher 1973). Such an effect is not reported for sites in western Canada (Peschken and Wilkinson 1981), but no discussion of possible ecotypic differences is included.

At the present time, none of the insects being tested as biological control agents has been simultaneously tested for tolerance to herbicides (Trumble and Kok 1982). It appears that 2,4-D at low rates can be used in conjunction with the rust Puccinia punctiformis to achieve better control than either treatment alone (Haggar et al. 1986).

Monitoring Requirements: Monitoring may be required to judge the effect of control measures in natural areas. In cases like C. arvense where natural succession may accomplish long-term control and "treatment" is mostly a matter of public relations, monitoring can measure changes in thistle populations as the community matures.

The best time to search for C. arvense is just before the blooming period, which varies from south to north, but corresponds with 14- 18 hours of daylight (Linck and Kommedahl 1958, Hunter and Smith 1972).

Because of the patchy growth and ability to regenerate from roots and root fragments, measurement of patch size by the line intercept methods may be more meaningful than actual stem counts.

If comparable methods of control are used from year-to-year throughout the same area, the number of person-hours required from control can provide a rough measure of effectiveness. A certain minimum number of hours will be required to search the tract regardless of the number of thistles encountered.

Management Programs: The Minnesota Chapter of The Nature Conservancy manages thistles on its preserves by mowing once annually just at the first onset of blooming. Contact Brian Winter or Rick Johnson, TNC, MN Field Office, 1313 5th Street S.E., Minneapolis, MN 55414. (612) 379-2207.

At Kilen Woods State Park, Minnesota, annual spot application of glyphosate to individual thistles has reduced infestations in treated areas. This control program is fairly labor intensive because it involves treatment every 2 to 3 weeks throughout the summer to assure that no thistles have been missed. Contact Lowell Jaeger, Park Manager, Kilen Woods State Park, MN.

Monitoring Programs: The Minnesota Field Office of The Nature Conservancy keeps track of the person-hours involved in thistle control as a measure of the effectiveness of its control program. Contact Brian Winter or Rick Johnson, TNC, Minnesota Field Office, 1313 5th St. S.E., Minneapolis, MN 55414. (612) 379-2207.
Management Research Needs: Research needs in natural areas differ from those in agricultural systems where continuous disturbance by cultivation or grazing creates continuing new thistle habitat. Natural area managers need to know what factors influence the development of new shoots from established thistle patches. Research priorities include the following: Is shoot development related to light penetration? Could fire actually favor the thistle development by reducing litter and competition for light? How effective are lateral roots in penetrating the sod of an established natural grassland?
Population/Occurrence Delineation Not yet assessed
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank)
Disclaimer: While I-Rank information is available over NatureServe Explorer, NatureServe is not actively developing or maintaining these data. Species with I-RANKs do not represent a random sample of species exotic in the United States; available assessments may be biased toward those species with higher-than-average impact.

I-Rank: High/Medium
Rounded I-Rank: High
I-Rank Reasons Summary: Cirsium arvense is a widespread, well recognized non-native that is on the majority of states' noxious species lists. The possible ecological effects are not well described, with mechanisms associated with greater density, extensive root system and perhaps chemical exudates. It is difficult to manage C. arvense, in part because of it's reproductive ability.
Subrank I - Ecological Impact: Medium/Low
Subrank II - Current Distribution/Abundance: High
Subrank III - Trend in Distribution/Abundance: Medium/Low
Subrank IV - Management Difficulty: High/Medium
I-Rank Review Date: 13Sep2004
Evaluator: Fellows, M.
Native anywhere in the U.S?
Native Range: Temperate Asia (Thunhorst and Swearingen 2001) Africa and Europe (Nuzzo 1997).

Download "An Invasive Species Assessment Protocol: Evaluating Non-Native Plants for their Impact on Biodiversity". (PDF, 1.03MB)
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Screening Questions

S-1. Established outside cultivation as a non-native? YES
Comments: (Kartesz 1999).

S-2. Present in conservation areas or other native species habitat? Yes
Comments: A problem species in national parks and on Nature Conservancy sites (Thunhorst and Swearingen 2001).

Subrank I - Ecological Impact: Medium/Low

1. Impact on Ecosystem Processes and System-wide Parameters:Low significance/Insignificant
Comments: No significant effects reported.

2. Impact on Ecological Community Structure:Medium/Low significance
Comments: One plant can colonize an area 3 - 6 feet in diameter in one or two years (Beck 2004). Roots may extend 15 feet horizontally and 6 to 15 feet deep (Beck 2004). Damages the structure of native species habitats (Nuzzo 1997; Thunhorst and Swearingen 2001).

3. Impact on Ecological Community Composition:Moderate significance
Comments: Displaces native species through competition for soil resources, space and light and may release chemical toxins (Nuzzo 1997; Thunhorst and Swearingen 2001).

4. Impact on Individual Native Plant or Animal Species:Low significance
Comments: Will hybridize with Cirsium hookerianum (NWCB 2003).

5. Conservation Significance of the Communities and Native Species Threatened:Medium/Low significance
Comments: Prairies and riparian/wetland areas (Nuzzo 1997; Thunhorst and Swearingen 2001; NWCB 2003)

Subrank II. Current Distribution and Abundance: High

6. Current Range Size in Nation:High significance
Comments: Throughout the northern and western US (Kartesz 1999; NRCS 2004). Absent from the southeastern US (TX to FL) and HI (Kartesz 1999).

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:High significance
Comments: Considered noxious in over 75% of the states in which it is present (Kartesz 1999; Thunhorst and Swearingen 2001).

8. Proportion of Nation's Biogeographic Units Invaded:High significance
Comments: Probably over 75% of ecoregions - inferred from current distribution (Kartesz 1999; NRCS 2004), preferred habitats and distribution of ecoregions (TNC 2001).

9. Diversity of Habitats or Ecological Systems Invaded in Nation:High significance
Comments: Non-forested communities like disturbed areas, prairies, barrens, savannas, glades, sand dunes, fields and meadows (Thunhorst and Swearingen 2001). Also present in wet areas with fluctuating water levels like streambank sedge meadows and wet prairies (Thunhorst and Swearingen 2001). "Nearly every upland herbaceous community within its range" (Nuzzo 1997).

Subrank III. Trend in Distribution and Abundance: Medium/Low

10. Current Trend in Total Range within Nation:Medium/Low significance
Comments: Follows disturbance (Thunhorst and Swearingen 2001; Beck 2004), but already widespread (Kartesz 1999; NRCS 2004).

11. Proportion of Potential Range Currently Occupied:Low significance
Comments: Inferred from current distribution (Kartesz 1999) and habitat types.

12. Long-distance Dispersal Potential within Nation:High significance
Comments: Wind dispersed seeds (Thunhorst and Swearingen 2001). Seeds also spread by water, attached to animals and humans, farm equipment and other vehicles (Beck 2004).

13. Local Range Expansion or Change in Abundance:Unknown

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:Low significance
Comments: Follows disturbance (Thunhorst and Swearingen 2001; Beck 2004).

15. Similar Habitats Invaded Elsewhere:Low significance
Comments: A near global distribution in like habitats(Nuzzo 1997)including: Canada (Kartesz 1999), South Africa, New Zealand and souteastern Australia (NWCB 2003).

16. Reproductive Characteristics:High significance
Comments: Large number of seed; viable seed bank up to 20 years; vegetative along root stock; vegetative from root fragments (Thunhorst and Swearingen 2001; Beck 2004).

Subrank IV. General Management Difficulty: High/Medium

17. General Management Difficulty:Moderate significance
Comments: Must kill entire plant by root removal or by herbicide treatment (Thunhorst and Swearingen 2001). Repeated applications are usually necessary (Thunhorst and Swearingen 2001; Beck 2004). Maintaining a healthy natural community can reproduction and growth of C. arvense (Beck 2004).

18. Minimum Time Commitment:High significance
Comments: A seedbank may remain viable for 20 years (Thunhorst and Swearingen 2001; Beck 2004).

19. Impacts of Management on Native Species:High/Moderate significance
Comments: Many native thistles occur in the US which could be misidentified as C. arvense (Thunhorst and Swearingen 2001). Non-target damage could result from herbicide spraying. Bio-control agents used for non-native thistles may also affect native thistles.

20. Accessibility of Invaded Areas:Low significance/Insignificant
Comments: Not a useful plant, so accessibility issues are inferred to be minimal.
NatureServe Conservation Status Factors Edition Date: 08May1987
NatureServe Conservation Status Factors Author: N. Sather
Management Information Edition Date: 08May1987
Management Information Edition Author: N. SATHER
Element Ecology & Life History Edition Date: 08May1987
Element Ecology & Life History Author(s): N. SATHER

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