Family: Asteraceae (Aster family)
Duration and Habit: Biennial, Perennial Forb/Herb
Spotted knapweed is a biennial to perennial with sever branched upright stems growing from a sturdy taproot up to 5 feet in height. Deeply lobed, pale, grayish green leaves become smaller as they grow higher up the stem. Stems are slender and hairy, growing upright, stiff and branched. A single plant can have over 100 flower heads. Flowers are pink to purple and can occasionally be white, growing at the ends of the branches. Flower heads (excluding flowers are approximately 1/4 inch in diameter and 1/2 inch tall. Bracts are present around the flower head and have distinctive vertical veins below a black triangular shaped spot on the bract tip.
Ecological Threat: Spotted knapweed will dominate sites without management, lowering plant community diversity and decimating forage production. When well established, it can occupy over 95% of the available plant community.
Biology & Spread: This species rapidly colonizes disturbed areas, including overgrazed pastures and rangeland, but is capable of establishing and persisting in well-managed rangeland.
History: It is believed to have been introduced to the United States from Asia or Germany as a contaminate in alfalfa seed. It rapidly spread throughout the United States in rangeland and has become widespread in the west and Canada.
U.S. Habitat: This species rapidly colonizes disturbed areas, including overgrazed pastures and rangeland, but is capable of establishing and persisting in well-managed rangeland. Gravel pits, waste sites and rights-of-way are also suitable habitat.
U.S. Nativity: Introduced to U.S.
Native Origin: Spotted knapweed is native to central, eastern and southeastern Europe.
U.S. Present: WA, OR, CA, AK, ID, MT, WY, NV, UT, AZ, CO, NM, ND, SD, NE, KS, LA, AR, MO, IA, MN, WI, MI, IL, IN, KY, TN, MS, AL, FL, SC, NC, VA, WV, OH, ME, VT, NH, NY, PA, MA, RI, CT, DE, MD
Distribution: Currently, this species has only been found at one location in Travis County, Texas.
Prevention is the best management for spotted knapweed, always clean equipment, pets, boots and vehicles to prevent inadvertently moving seeds in the environment.
Small infestations and single plants can be effectively managed by hand pulling or digging. If flower parts have formed, be sure to carefully bag and dispose of all parts when manually removing the species. Mowing is not effective, as the plant will flower and set seed below the mow level.
For large or well established infestations, it is most effective to apply a selective, broadleaf herbicide prior to the plant flowering.
Pacific Northwest Weed Management Handbook. 2014. Oregon State University.
Invasive Plant Atlas of the United States
King County Noxious Weed Control Program
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