: Centaurea nigra L. var. radiata
: Lesser knapweed
: Introduction to the United States is unknown.
: Perennial knapweed, with purple flowers and black bracts growing up to 5 feet tall.
: Basal leaves have leaf stalks and are narrow with the widest point near base of leaf or in the middle. Stem leaves become smaller and narrower moving up the stem and stalkless. Margins are slightly toothed or smooth.
: One to many branching stems covered in hairs. Upright and growing up to 5 feet tall.
: Flowerheads occur at branch tips. Bracts at base of flowerhead covered with dark brown or black fringed margins up to 3 times as long as bract. Flowerheads are made up oprimarilyf 40 to 100+ purple (or sometimes white) flowers.
Fruit and seeds
: Seeds may have short blackish unequal bristles on one end that can fall off
: Native to Europe and Russia. Found in open grasslands, prairies, open forests, orchards, cultivated fields, field edges, and travel corridors.
: By seed and can regenerate from crown or by rhizomes.
: Other species of knapweed (Centaurea
Monitoring and rapid response
: Hand pull plants, removing the entire tap root. Mow or cut plants before flowering to prevent seed-set. Herbicide treatments are most effective when combines with other control techniques. 3% solution of triclopyr herbicide mixed with water can be applied to leaves in early spring or fall. Gall flies (Urophora affinis
and Urophora quadrifasciata
) are used to feed on developing seed heads.
: The information provided in this factsheet was gathered from the Wisconsin Department of Natural Resources and the Washington State Noxious Weed Control Board.
Individual species images that appear with a number in a black box are courtesy of the Bugwood.org network (http://www.invasive.org).Individual photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (http://images.google.com).