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 pf Washington.

Why Should I Care?

Knapweeds may impair wildlife habitat, decrease plant diversity, and increase soil erosion. They also may 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.

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. Promote native or desired species to help prevent or limit initial infestations.

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 they are prohibited to transport, buy, sell, offer for sale, or distribute these plants, plant parts, or seeds. Also, many knapweed species including yellow starthistle are listed as Class B noxious weeds, meaning that they are designated for control in certain state regions. Contact your county noxious weed coordinator for assistance.

To learn more, visit our “Don’t Pack a Pest” and “Play, Clean, Go” campaign pages.

What Are Their Characteristics?

Knapweeds in General

  • Knapweed grows up to 3 feet tall.
  • They are yellow, white, pink, and purple.
  • Knapweed flowers resemble small thistles growing at the end of clustered branches.

Yellow starthistle

  • Grows to be 18-36 inches tall, with a deep taproot.
  • Has alternate leaves with bases extending downward, producing a winged effect.
  • Stems are dull green and covered with woolly hairs.
  • Yellow flowers are thistle like, with short yellowish spines in star-like arrangement at the base of the flower head.

Additional Photographs