Russian knapweed identification and control
Russian knapweed (Rhaponticum repens) is a bushy, branched perennial in the Aster family reaching 1 to 3 feet tall and forming clones or colonies from vigorous, deep, spreading rhizomes. It has numerous, small, thistle like flower heads that are pink to purple in color. The bracts under the flower heads are greenish to straw colored and have a broad, papery tip. Leaves at the base of the stem (basal leaves) are gray-green and lobed. Upper stem leaves are smaller with toothed edges or entire (smooth) edges. Stems are upright, branched and hairy. Young plants are whitish and woolly.
Russian knapweed is an aggressive invader of pastures, non-crop areas, grain fields and other cultivated fields. In addition, the plant is poisonous to horses, causing chewing disease (equine nigropallidal encephalomalacia). It is a Class B noxious weed designated by the State Noxious Weed Board for required control in King County. It is rarely found growing in King County. For more information on the noxious weed law and list, see Noxious weed lists and laws.
Russian knapweed is a difficult plant to control due to deep spreading rhizomes. All parts of the plant should be discarded in the trash to avoid spreading it.
Additional information on Russian knapweed
- Washington State Noxious Weed Control Board (external link)
- Selected Knapweeds of Washington (316 KB Acrobat file)
What to do if you find this plant in King County, Washington
Please notify us if you see Russian knapweed growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because Russian knapweed is not established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as Russian knapweed in order to help us and others locate new infestations in time to control them.
Report Russian knapweed in King County, Washington
- Please notify us through our online infestation form
Locate Russian knapweed in King County, Washington
- Use our interactive noxious weed map and search for Russian knapweed