John M. Randall, The Nature Conservancy,
Bugwood.org
Family: Asteraceae (Aster family)
Synonym(s):
Duration: Biennial, Perennial
Habit: Forb/Herb
Listed by:
Invasive Plant Atlas of the US: 1
Federal Noxious Weed: 0
TDA Noxious Weed: 0
TPWD Prohibited Exotic Species: 0
Description: 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.
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.
Biology & Spread: This species rapidly colonizes disturbed areas, including overgrazed pastures and rangeland, but is capable of establishing and persisting in well-managed rangeland.
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.
US 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.
Distribution
US Nativity: Introduced to U.S.
Native Origin: Spotted knapweed is native to central, eastern and southeastern Europe.
US States: 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
Resembles/Alternatives:
Management: 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.
USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
Listing Source
Texas Department ofAgriculture Noxious Plant List
Texas Parks and Wildlife Department Prohibited Exotic Species
Invaders Program
Federal Noxious Weed
Union of Concerned Scientists
United States Forest Service Southern Research Station
Text References
Pacific Northwest Weed Management Handbook. 2014. Oregon State University.
Data Source
Invasive Plant Atlas of the United States
King County Noxious Weed Control Program
Last Updated: 2014-06-26 by JDB