California Invasive Plant Council

Cirsium arvense

Common names: Canada thistle

Cirsium arvense (Canada thistle) is a perennial (family Asteraceae) found scattered throughout California, except in the Sonoran and Mojave Deserts and the southern Sierra Nevada. Canada thistle forms dense patches which may crowd out native vegetation. This clump-forming plant reproduces by seed and vegetatively from its extensive root system. Control is difficult because root fragments as small as 1 cm can sprout to form a new plant, and seeds are dispersed by small animals, wind and human activities. Occasional cultivation may increase Canada thistle populations by dispersing root fragments, but control can be achieved with continued cultivation, mowing or hand-cutting.

Cal-IPC Rating: Moderate

Cal-IPC Assessment

Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.

Species ID Card

Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.

Weed Management Notes

• Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

• Eradication in the central Sierra. Cal-IPC. Vol 24, Issue 1
• Weed biological control agents approved for California. Pitcairn, Michael J.; Smith, Lincoln; Moran, Patrick. Vol 22, Issue 1
• Feed the birds, but don’t spread weeds. America, Weed Science Society of. Vol 17, Issue 2
• Fighting weeds in the Tahoe basin. Donaldson, Sue. Vol 11, Issue 2
• California Exotic Pest Plant Council draft list exotic plants of greatest concern October 1993. CalEPPC. Vol 01, Issue 4

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

• Preventing weed spread via contaminated hay and straw. Clines, Joanna (2005)
• Getting the job done: Working within the regulatory environment at Lake Tahoe to manage weeds. Donaldson, Susan; West, Wendy; Taylor, Kirk (2003)
• Risk analysis of various weed control methods. DiTomaso, Joseph M. (1997)
• Using Transline* herbicide to control invasive plants. Carrithers, Vanelle F. (1997)

Other Cirsium arvense Information

• CalPhotos - Images of plants taken mostly in California.
• Calflora - See the distribution of this species on Calflora's map of California.
• CalWeedMapper - Distribution information with ability to determine regional priorities.
• Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
• CDFA - California official noxious weeds.
• USDA PLANTS Database - Federal database with information on identification and distribution, and links to websites in individual states.
• Bugwood - National database from the Center for Invasive Species and Ecosystem Health at the University of Georgia.