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bighead knapweed flower

Bighead knapweed is a large, perennial herb with yellow, globe shaped flower heads that are about 1 - 3 inches in diameter and grow singly on tops of stems. The plant grows on sturdy root stock and can reach five feet tall. This plant spreads by seed and it has the capability to establish in natural areas, particularly in subalpine meadows.

This knapweed is very limited in distribution in Washington State.  The largest infestation is in Pend Oreille County, where control work on a 10 acre site has been in progress since 1990. However, it is sometimes found as a garden ornamental or in cut flower arrangements.  It is also known by the common names pineapple thistle and globe centaury.

Legal status in King County, Washington

Bighead knapweed is a Class A noxious weed in Washington and property owners are required to eradicate it from their property.  It is also on the Washington quarantine list (also known as the prohibited plants list) and it is illegal to buy, sell or offer it for sale in the state of Washington. For more information on noxious weed regulations and definitions, see Noxious weed lists and laws.

Additional information on bighead knapweed

What to do if you find this plant in King County, Washington

Please notify us if you see bighead 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 bighead 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 bighead knapweed in order to help us and others locate new infestations in time to control them.

Bighead knapweed photos

bighead knapweed plants
bighead knapweed
bighead knapweed

Report bighead knapweed in King County, Washington

Locate bighead knapweed in King County, Washington

Additional resources

Related information

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Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).