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  Weed Identification

Russian Knapweed


  • Russian Knapweed | Source: National Agricultural Library, Agricultural Research Service, U. S. Department of AgricultureStems: Up to 3 ft tall and branched.
  • Leaves: Lower leaves long, generally lobed; Upper leaves smaller, toothed or entire. Leaves are 6 inches long at base, and get smaller towards top of plant.
  • Flowers: Flowering heads are narrow, flowers are about 1/2-inch wide, pink to lavender. Flowering period is from June to September.
  • Seeds: Ivory colored, obscurely striped, 1/8-inch long, at first tipped with bristle tuft of unequal length.

 

Russian knapweed is a woody perennial that can form dense colonies. The entire plant is more or less white woolly when young. It infests alfalfa and grain fields, irrigation ditches and waste areas. It spreads by seed and rootstock and can produce up to 27 rootshoots a year. The deep, extensive root system (up to 23 feet) makes it especially difficult to control. It emits a substance that inhibits the growth of other plants around it. The leaves are bitter and unpalatable to livestock. Causes "chewing disease" (trachea paralysis) in horses. ***WARNING: All knapweeds may contain a cancer causing agent -- Handle with extreme caution!***

Control:

  • Biological: Sheep graze the new growth while it is succulent, but this is not particularly effective. Reseeding with fast growing grasses can prevent new invasions. Seedhead flies can reduce it a bit.
  • Mechanical: Continuous tillage combined with herbicide application can be effective. Otherwise, tillage or pulling only serves to spread it. Wear gloves when pulling!
  • Chemical: Most effective application is during the early bud stage. Consult your Weed Board for more details.
    • Source: USDA Forest Service

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