This is a biennial or short-lived perennial growing up to 3 feet tall.
It reproduces by seed and each plant can produce up to 1,000 seeds per plant.
Flowers are single, vase-shaped, and pinkish-purple. The involucre bracts are stiff and tipped with a dark comb-like fringe which gives the base a “spotted” appearance.
Leaves are grayish-green, alternate, and upper leaves are very reduced.
Spotted knapweed was introduced into the US as a contaminant in alfalfa seed from Asia in the early 20th century. It is now found in every county of every state west of the Mississippi! Highly competitive, this plant can rapidly take over native range and destroy habitat for wildlife and livestock. In Natrona County it is found mainly in the Casper area and along the highways .
Chemicals must be applied before the plant produces seed to be effective. Contact your local weed and pest for specific chemical recommendations.
There are currently seven species of biocontrol insects released on this plant in Natrona County.
Cut, pull, or dig up before seed production.