Idaho OnePlan recommends the website of the Idaho Weed Awareness Campaign as the best resource for up-to-date information about Idaho's noxious weeds, and their control.
Source for this page: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller

BACKGROUND

Meadow knapweed (Centaurea pratensis) is a native of Europe and can grow in a wide range of environmental conditions. Meadow knapweed is believed to be a fertile hybrid resulting from crossbreeding black knapweed (C. nigra) and brown knapweed (C. jacea).

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DESCRIPTION

Meadow knapweed is a perennial plant up to 3 feet tall. BasalAt the base of plant or plant part leaves are up to 4 inches long, slender, have a petioleA leaf stalk, and may be entireNot toothed or otherwise cut, toothed, or lobedA cut into a leaf from the edge toward the center; greater than toothed, but not quite compound. Stem leaves usually don't have a petiole and are much smaller. Stems are many branched and tipped by a solitary flower head up to 1 inch wide. Flowers are pink to reddish-purple and are produced from midsummer through fall. Flower head bractsLeaflike structure at the base of flowers or leaves are inch wide, and the tips range from a comblike fringe to a blunt ruffled edge. Bract tips range from tan to dark brown or, rarely, black. Seeds are brown to gray in color and are tipped by plumesA hairlike or featherlike structure, often on a seed that fall off at maturity.

DISTRIBUTION

Meadow knapweed is found from British Columbia to northern California.

CONTROL

A biological control agent (a seed head gall fly) has provided fair control of meadow knapweed in Washington, but is still under evaluation in Idaho. Herbicides are available for control.