Russian knapweed
      (Centaurea repens L.)
      (Acroptilon repens),  Asteraceae.
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      Roots: the roots are horizontal and vertical (up and down, and left to right) in the ground, they may be black and the roots also creep, the roots can be from 6 to 27 roots per square foot (3), they also can grow to a depth of 23 feet. (3)

      Photo by Ron Lang, USDA-APHIS-PPQ.  WY.
      Stems/Leaves: the stems are erect and branched openly, they can be from 18 to 36 inches tall.  Lower leaves are 2 to 4 inches long and the upper leaves are very narrow. The stems can also be ridged and stiff and branched, the younger stems are covered with the soft gray hairs, the upper leaves are small also, leaves that are at the middle of the stem have toothed margins. (2)

      Flowers: the flowers are cone-shaped and the heads are 1/4 to ½  inches in diameter. They are solitary at the tip of the stem, the ray flowers are  pink to lavender, they can be un-shaded,  when they mature the color becomes a straw color in the fall, they are borne on branch tips during the summer and the fall. Flowering occurs from June to August. (5)

      Fruits/Seeds: the flowers have a thistle like texture, are 1/3 to 1/4" in diameter and are lavender to white in color. The seeds are flattened, ivory color, 2-3 mm long, 2 mm broad, 1 mm thick, and have small bristles. The  bristles of the seeds are white. (5)

      Methods of Reproduction: it reproduce by creeping roots and by seeds. (1)

      Montana Infestation:

      Environments of Infestations: Russian knapweed will grow in cultivated fields, fence rows, roadsides, along ditch banks, and in wasted places (1), it can occur in most soils in the U.S. (4)

      Comments: Russian knapweed is a very large problem that is growing within the United States. This noxious weed is a problem that everyone needs to work to control. This summer I personally spent time spraying the weed and I think it is a problem.

      Impacts: Russian knapweed is very poisonous to horses and it will give them a  chewing disease. (2)

      Native Range: It is a native of Eurasia and was probably introduced in 1898.

      Methods of control: The biological agent that controls it is called gall nematode (Subanguina picridis) and is available for Russian knapweed control. The control levels have not yet been determined. (3)

      How to Prevent Spread: To stop spread be careful when you are walking in fields and get some seeds on you, then just wipe them off.  Also, when you close your car door in a field make sure that you don't have any seed heads sticking in as this will trap them and you will inadvertently transport them as you drive to a new area where they may fall out of your car and cause a new infestation.  Be sure and wash the undercarriage of your car after you have driven in Russian knapweed infested areas.  Do not transport soil with root fragments and/or seeds in it.

      Bibliography:

      1. Russian Knapweed (Centaurea repens L.) [Online] Available: Http://www.fortnet.org/CWMA/russian.htm
       
       2. CSU/Arapahoe County Cooperative Extension Copyright © 1999, This page maintained by Russell Johnson, Weed Control Inspector,  5334 S. Prince St., Littleton, CO  80166 (303) 738-7861, [Online] Available: http://www.arapcsuext.org/agri/russ.htm

       3. Robert H. Callihan & Timothy W. Miller. RUSSIAN KNAPWEED.  [Online] Available: http://www.oneplan.state.id.us/pest/nw25.htm

       4. Ecology and Distribution of Acroptilon repens. [Online] Available: http://www.usgs.nau.edu/swemp/Info_pages/plants/Acroptilon/Russianknapweed.html
      September, 1999. Webmaster: jjg@usgs.nau.edu .

       5.Lyle Holmgren, USU Extension Agent. Russian knapweed text. [Online]  Available: http://www.ext.usu.edu/agline/htmweeds/ruknp_tx.htm     September, 1999.

      By: Woody
      Edited By: Mike Roylance      11/4/99.
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