Diffuse knapweed was introduced from Europe and is a biennial or short-lived perennial forb which reproduces only by seed. The plant usually produces a single main multi-branched stem that is 1.5 to 2 feet tall. The flower is white or pink with bracts.
The largest infestation in Garfield County can be found west of the Riverbend subdivision southeast of New Castle. It is also scattered along Interstate 70 between Rifle and Parachute, south of Glenwood Springs at the Glenwood Airport, and throughout the old rodeo grounds and Rifle Creek Golf Course.