Images courtesy of Eric Coombs, Oregon Dept. of Agriculture.
If images are downloaded and used from the ODA web site please be sure to credit the photographer.
Description Biennial or short-lived perennial; blooms midsummer to fall. Grows up to 3 feet tall. Multi-stemmed plant with several stems arising from crown. Flowers purple or rarely cream colored. Tips of flower head bracts are usually black, thus the name "spotted." Seeds dispersed by wind, animals, and people.
Impacts Spotted knapweed is one of the most dominant weed species in the western United States. Millions of acres of prime range and native habitat are infested throughout the northern Rocky Mountain states. Infested acres in Oregon is still limited but increasing and has caused economic losses of approximately $54 million dollars in the state. This species will form dense stands on any open ground, excluding more desirable forage species and native plants. On heavily infested range, the necessary control measures to recover the land are often more expensive than the income potential derived from grazing. Control success is hampered by seed longevity. Weeds of the Centaurea genus have more negative impacts to natural and agricultural ecosystems than any other.
Introduction A European import thought to be introduced to Pacific Northwest in ship’s ballast.
