Britt Slattery, USFWS

Canada Thistle
Cirsium arvense

Canada thistle, a perennial member of the aster family and a native of temperate regions of Eurasia, was introduced to the United States during the 1600s and is designated as a noxious weed in 43 states. It invades a variety of dry to moist habitats including barrens, fields, glades, pastures, stream banks, wet meadows and wet prairies. Canada thistle displaces native plants, changes the structure and species composition of natural plant communities and reduces biodiversity. Abundant seeds germinate within a year, but seeds remain viable for at least 20 years. It also spreads vegetatively, through lateral roots and root fragments.

Prevention and Control
Many native species of thistle occur in the United States, including some that are very rare. Positive identification of Canada thistle should be made before any control is attempted. Management includes long-term hand-cutting, mowing, controlled burning or chemical means, depending on the level of infestation and the type of area being managed.

Native Alternatives
After eradicating, plant area with native vegetation appropriate to site conditions. Refer to References.

---

Publication by USFWS BayScapes Conservation Landscaping Program
http://www.nps.gov/plants/alien/pubs/midatlantic/ciar.htm
Last updated: 7 October 2004