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.Rating: Moderate
- 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.
- CalWeedMapper - Statewide maps, climate models, and reports.
- Cal-IPC News - Our quarterly newsletter. Each issue is available as a pdf.
- Cal-IPC Symposium Proceedings - Presentations and papers from our annual Symposium.
- Don't Plant a Pest! - Select your region to find non-invasive alternatives to ornamental species. Also see our statewide brochure on trees.
- Species account from Invasive Plants of California's Wildlands - Includes biology and management information.
- USDA PLANTS database -
Federal database with information on identification and distribution, and links to websites in individual states.
- Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from the UC Berkeley Jepson Herbarium.
- CalFlora - Distribution information by county based on submitted observations and herbarium specimens.
- The Nature Conservancy Management Summary - Information compiled by TNC land managers. Photos included for some species.
- CalPhotos - Images of plants taken mostly in California.
- Natural Resource Projects Inventory - State database with information on resource management projects throughout California. Query by the species of interest.
- Carrithers, V., B. Miller, et al. (2005). Aminopyralid: A new reduced risk active ingredient for control of broadleaf invasive and noxious weeds. California Invasive Plant Council Symposium 2005. Chico, California, California Invasive Plant Council.
- Carrithers, V. F. (1997). Using Transline* herbicide to control invasive plants. California Exotic Pest Plant Council Symposium '97. Concord, CA.
- Clines, J. (2005). Preventing weed spread via contaminated hay and straw. California Invasive Plant Council Symposium 2005. Chico, California, CA.
- DiTomaso, J. M. (1997). Risk analysis of various weed control methods. California Exotic Pest Plant Council Symposium '97. Concord, CA.
- Donaldson, S., W. West, et al. (2003). Getting the job done: Working within the regulatory environment at Lake Tahoe to manage weeds. California Invasive Plant Council Symposium 2003. Kings Beach, CA.
- Smith, R. L., V. F. Carrithers, et al. (2006). Managing rangeland invasive plants with Aminopyralid (MilestoneTM). Cal-IPC Symposium. Rohnert Park, CA.
Cal-IPC News Articles
- Weed Science Society of America (2009). Feed the birds, but don't spread weeds. Cal-IPC News. 17: 12.
- (1993). California Exotic Pest Plant Council draft list exotic plants of greatest concern October 1993. CalEPPC News. 1: 6.
- Donaldson, S. (2003). Fighting weeds in the Tahoe basin. CalEPPC News. 11: 7.
- Pitcairn, M. (2000). All weeds that have approved biological control agents, accidental introductions and others. CalEPPC News. 8.
- Richardson, B. (2004). The A-rated north. Cal-IPC News. 12: 4-5,14.
- Smith, R. L., V. F. Carrithers, et al. (2006). Managing rangeland invasive plants
with Aminopyralid (MilestoneTM). Cal-IPC Symposium, Rohnert Park, CA, California Invasive Plant Council.