Invasive Plant: Spotted Knapweed

Click on image for full size viewDescription:
Biennial or short lived perennial.  Spotted knapweed produces a toxin via the roots that kills plants within its root zone.  The plant can have one or more shoots up to 4 feet tall. Rosette leaves can be six inches long and deeply lobed. Leaves on shoots are smaller and finely divided, becoming smaller toward the top of the shoot, and are covered with fine hair.  In mowed areas of Becker County the plant will bloom and produce seeds at 4-6" high.

Spotted knapweed occupies dry meadows, pastures, stony hills, roadsides, and the sandy or gravelly flood plains of streams and rivers where soils are light textured and well drained.

Spotted knapweed seed may spread by vehicles, including ATVs, livestock feed, hay used as mulch, and contaminated crop seed or gravel.

Control:

• Biological - Spotted Knapweed Seedhead Weevil and Root Weevil. The Becker County SWCD placed 450 weevils at 5 sites since 2006.  It takes up to 10 years for a weevil harvesting site to be developed.
• Cultural - Hand pulling (wear gloves) is effective in small infestations.  Seed bank is 5 or more years, so don’t disturb the soil.  Mowing, clipping, and burning may be somewhat effective in controlling, but not eradicating populations.  Do not mow when plant has gone to seed, this will distribute the seed.
• Chemical - Access, Crossbow, ET, Garlon, Grazon, PathFinder, Redeem, Rely, Remedy, and Turflon, Banvel, Banvel + 2,4-D, Transline, Transline + 2,4-D, and Transline-monoea salt have been used effectively. To deplete the seed bank treatment may be necessary for several years. 

Photo Credits:  Marsha Watland – BSWCD and Missouri Weed ID Guide 
Resources: Carol Estes Mortensen, Leech Lake Division of Resources Management, NDSU Extension Service, Marsha Watland (BSWCD) - funding National Fish & Wildlife Foundation.