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)
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.
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
Be sure and wash the undercarriage of your car after you have
Russian knapweed infested areas. Do not transport soil
fragments and/or seeds in it.
1. Russian Knapweed (Centaurea repens L.) [Online]
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.
September, 1999. Webmaster: firstname.lastname@example.org .
5.Lyle Holmgren, USU Extension Agent. Russian knapweed