What are they?
Knapweeds, such as bighead, black, brown, diffuse, meadow, spotted, and vochin knapweeds, are perennials, native to Europe. They grow very aggressively and quickly can infest an area if left unchecked.
Are they here yet?
Yes. Knapweeds are found in various parts of Washington, depending on the species.
Why should I care?
Knapweeds can impair wildlife habitat, decrease plant diversity, and increase soil erosion. They also can cause crop losses and reduce forage, decrease the appeal of recreational lands, and pose wildlife hazards. Diffuse knapweed has spines that can damage the mouths and digestive tracts of livestock, significantly reducing forage opportunities.
What should I do if I find one?
How can we stop them?
Limit the transport of knapweed seeds by cleaning animals, vehicles, and personal gear before moving from an infested or potentially infested area, and by using weed-free seed.
Do not collect knapweed flowers or plants as ornamentals – diffuse, brown, meadow, spotted, bighead, black, and vochin knapweeds are on Washington’s Terrestrial Noxious Weed Seed and Plant Quarantine list, meaning it is prohibited to transport, buy, sell, offer for sale, or distribute these plants, plant parts, or seeds (Washington Administrative Code 16-752-610). Also, many knapweed species are listed as Class B noxious weeds, meaning that they are designated for control in certain state regions.
What are their characteristics?
- Knapweeds grow 1-3 feet tall.
- They are yellow, white, pink, or purple.
- Knapweed flowers resemble small thistles growing at the end of clustered branches.
- For more information on how to distinguish Centaurea species, see:
Where can I get more information?
Knapweeds in general
Bighead knapweed (C. macrocephala)
Black knapweed (C. nigra)
Brown knapweed (C. jacea)
Diffuse knapweed (C. diffusa)
Meadow knapweed (C. pratensis)
Spotted knapweed (C. biebersteinii)
- King County Spotted Knapweed Identification
- Whatcom County Spotted Knapweed Identification
- Washington State Noxious Weed Control Board
- Little Things, Big Problems - Spotted Knapweed
Vochin knapweed (C. nigrescens)