Russian knapweed

Acroptilon repens

   

Family: Asteraceae

Other common names: hardheads, Turkestan thistle

Weed Class: B

Year Listed: 1988

Native to: Russia and Eastern Europe

Toxic: livestock

Other Legal Listings:

additional photos

 

   

Why is it a noxious weed?

It is an aggressive invader of pastures, non-crop areas, grain fields and other cultivated fields. In addition, the plant is poisonous to horses, causing chewing disease (equine nigropallidal encephalomalacia). Livestock may avoid this species.

How would I identify it?

General Description: Russian knapweed is a bushy, branched perennial, reaching 1 to 3 feet tall and forming clones or colonies from vigorous, deep, spreading rhizomes.

Flower Description: Many flower heads, pink to purple in color. The outer bracts under the flower heads are greenish to straw colored and have a broad, papery tip.

Leaf Description: Leaves at the base of the stem (basal leaves) are gray-green and lobed. Upper stem leaves are smaller with toothed edges or entire (smooth) edges.

Stem Description: Stems are upright, branched and hairy. Young plants are whitish and woolly.

Fruit/Seed Description: Seeds (achenes) are ivory white and have a feather-like plume (pappus).

May be confused with:

How does it reproduce?

Russian knapweed reproduces by seed and spreads laterally by its root system. Root fragments can regenerate following cultivation.
 

Where does it grow?

Russian knapweed is found growing in pastures, hayfields, grain fields, irrigation ditches as well as roadsides. Please click here to see a county level distribution map of Russian knapweed in Washington.
 

How do I control it?

General Control Strategy

Productivity can be maximized in less time if Russian knapweed populations are treated with a suitable herbicide, farmed, and seeded to a competitive forage.

Cultural Control

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.

Biological Control

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

Herbicide Control

It is difficult to control with herbicide. Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.


 

For more information

 
See our Written Findings for more information about Russian knapweed (Acroptilon repens).

Additional Photos


 
 

 


Russian knapweed flowerhead

 


Russian knapweed infestation

 


Russian knapweed roots

 


Flowering plant

 


Russian knapweed after flowering

 


Russian knapweed infestation

 


Russian knapweed infestation

 


flowerheads post flowering

 


flowerhead in bloom

 


flowerhead in bloom top view

 


blooming flowerhead

 


bracts showing smooth, thin, translucent tips

 


blooming infestation

 


torn open flowerhead

    

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