• facebook
  • twitter
  • YouTube
  • RSS feed
  • 651-201-6000
  • 800-967-2474
  • 711 TTY

NodeFire Save Document
Home > Plants, Pests & Pest Control > Pest Management > Noxious & Invasive Weed Program > Weed of the Month > December 2014 - Brown, Meadow, and Diffuse Knapweeds

December Weed of the Month: Brown, Meadow, and Diffuse Knapweeds

Flower of meadow knapweed with bright pink petalsDecember’s Weed of the Month is not one, but three species of knapweed: brown knapweed (Centaurea jacea), meadow knapweed (C. x moncktonii), and diffuse knapweed (C. diffusa). All three species are native to Eurasia, and it’s thought they were introduced to western North America for forage. In Minnesota, infestations of meadow knapweed have been reported in St. Louis and Koochiching counties, brown knapweed has been reported in Koochiching County, and diffuse knapweed has been found in Duluth.

Several characteristics of these knapweed species have helped them thrive and become a threat to Minnesota. They outcompete pasture grasses and native plants, leading to large bare patches of soil that is more susceptible to erosion and water runoff. Once established, the knapweeds reduce hay quality and pasture productivity. The plants can also hybridize between species, which makes identification difficult and increases the risk for an aggressive plant that can invade many soil types and growing conditions.

Knapweeds can be biennial or perennial. They reproduce primarily by seed, which can be spread with infested hay, on equipment, or by wind and water movement. The flowers are tight clusters of individual flowers called florets. The flower color ranges from pink to white. The plants produce a rosette of leaves, which then sends up a flowering stalk in the summer.

To prevent the knapweeds from further spreading throughout Minnesota, several management strategies are available.

  • Make sure to clean equipment, vehicles, and footwear after being in a knapweed infested area.
  • A combination of hand-pulling and digging is an option for small infestations. Seedlings are tap-rooted and can be hand-pulled; however, the large taproots must be removed or the plant will regenerate from the root.
  • Herbicides are a very effective management tool for meadow knapweed. For specific herbicide recommendations, contact your University of Minnesota Regional Extension Educator.
  • Mowing does not control meadow knapweed and the mower may spread seed.
  • All infestations must be monitored and treated until the seedbank is depleted.

To report infestations of these species of knapweeds or any other noxious weeds on the eradicate list, please use the Early Detection and Distribution MAPping System.