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Class B Noxious Weed

Russian Knapweed
Acroptilon repens
 

Russian knapweed


Plant family: Compositae
Year listed: 1996
Native to: Russia

Why is it a noxious weed?

Russian knapweed is aggressive invading pastures, non-crop areas, grainfields and other cultivated fields. Livestock may avoid this species; in addition, the plant is poisonous to horses, causing chewing disease (equine nigropallidal encephalomalacia).

How would I identify it?
General Description: Russian knapweed is a bushy, branched perennial, reaching 1 to 3 feet tall forming clones or colonies from its vigorous, spreading root system.

Leaves:

  • basal are deeply notched
  • gray-green
  • upper are smaller, linear and have broken edges
  • stem leaves are intermediate with toothed edges

Flowers:

  • solitary
  • pink to purple
  • bracts under flower heads are greenish or straw colored, and have a broad, papery tip.

Stems:

  • erect
  • hairy
  • young plants are whitish and woolly, but then turn dark brown to black

How does it reproduce?
Russian knapweed reproduces by seed and spreads laterally by root system.

Where does it grow?
Russian knapweed is found growing in pastures, hayfields, grainfields, irrigation ditches as well as roadside.

What is the distribution in Washington State?

Click map to enlarge

 

  • Distribution map is based on 2003 data.

How do I control it?

General control methods: Productivity can be maximized in a minimum amount of time if Russian knapweed populations can be treated with a suitable herbicide, farmed, and seeded to a competitive forage.

Cultural: Depending on the moisture regime, nitrogen fertilizer applied in conjunction with an herbicide significantly improves the competitiveness of residual grasses. In addition, improved grazing management will significantly influence the life span of Russian knapweed control efforts.

Herbicide: Difficult to control with herbicide. Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.

Mechanical: Not known.

Biological: The nematode Subanguina picridis forms galls on Russian knapweed that
reduce plant vigor - its effectiveness in Washington is not yet known.

For more information
For more information, download our Written Findings.

 

More Photos-Click photo to enlarge
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Russian knapweed infestation Russian knapweed roots
Infestation of Russian knapweed. Root system of Russian knapweed. Russian knapweed plant.

 Last updated September 10, 2008