Russian knapweed is the most widespread of the knapweeds in North Dakota. It is also the only perennial of the noxious knapweeds and is the most difficult to control. Russian knapweed can spread rapidly and is very competitive with native species. Russian knapweed will reduce forage production to near zero as the site often becomes a monoculture. Russian knapweed also will infest roadsides, pasture and rangelands, and croplands causing significant crop losses.
Russian knapweed is a long-lived, deep-rooted perennial with growth characteristics similar to Canada thistle. It emerges in the spring from roots and grots to 2 to 3 feet tall and is shrub like with spreading branches. Once established, Russian knapweed spreads mainly by underground root stocks and seed production is limited. Flowering occurs from June to September and flower color varies from light pink to lavender. The stems die back to the soil surface each year.
Control on non-crop lands:
Chemical: Best control is obtained when Tordon (picloram) is applied following several hard frosts (mid-October). Russian knapweed plants may be dormant with gray stems and no leaves, but control the following spring is nearly 100 percent. Milestone and Escort are also effective.
Cultural: Livestock generally will not graze Russian knapweed. Mowing and cultivation do not control this weed.
Biological: Exploration and evaluation of biocontrol agents are in progress.