Scotch thistle is a member of the Aster family. It is a biennial that was introduced from Europe or eastern Asia and can reach a height of 8 feet. The rosette forms the first year and can have leaves up to 2 feet long and 1 foot wide. The second year the plant produces flowers that are reddish-purple to violet. It is found primarily along roadsides and railroads, but can become an impassable obstacle to livestock on rangeland and pastures. It is increasing in densities throughout Pitkin County.

Comments: Very rare in Pitkin County. A few plants located on the hillside behind Centennial, also a small infestation along Capitol Creek Road. A few infestations are found in the Town of Snowmass Village.

Biological controls: None currently available.

Chemical controls: For additional information contact your local city, county or town natural resource office. (See section VII for phone numbers.)

Cultural controls: Reseeding of disturbed sites with fast growing native grasses.

Mechanical controls: Digging the plant at the rosette stage is effective.

Locations of Infestations of Scotch Thistle on Roads and Open Space in Pitkin County: