Source: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller
BACKGROUND
Russian knapweed (Acroptilon repens) is an invader from the Caucasus in southern Russia and Asia. It spreads both by seed and from shoots arising from creeping roots. It can produce up to 27 root shoots/ sq ft, and roots may grow to a depth of 23 feet. Russian knapweed causes chewing disease in horses.
DESCRIPTION
Russian knapweed is a perennialPlant that lives for more than 2 growing seasons whose stems are considerably branched and up to 4 feet tall. Leaves are up to 6 inches long near the base of the plant, entireNot toothed or otherwise cut to few-toothed, and are smaller toward the top of the plant. The flower heads are about ½ inch in diameter and are borne on branch tips during summer and fall. The flowers may be white or pink to lavender-blue. Greenish to straw-colored bracts are tipped with a papery, pointed marginThe edge of the leaf. Ivory-colored seeds are tipped by plumesA hairlike or featherlike structure, often on a seed that fall off at maturity. Roots are dark brown to black.
DISTRIBUTION
Russian knapweed is found throughout the western U.S.
CONTROL
A biological control agent (a stem/leaf gall nematode) is available for control of Russian knapweed, but control levels have not been determined. Herbicides can provide excellent control.