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Home>Plant Species>Weed Species>Russian knapweed

Drawing of Russian knapweed Russian knapweed
Acroptilon repens (Centaurea repens)

question markDid you know?

If horses eat too much Russian knapweed, it can cause a fatal neurological disorder!

How did Russian knapweed get here?
Overall, knapweeds are a large group of over 400 species, many of which are considered invasive weeds. Russian knapweed is a native of Eurasia, probably introduced in North America about 1898 as a contaminant of Turkistan alfalfa.

What are its characteristics?
Russian knapweed could be the poster-child for noxious weeds. This perennial forb forms dense colonies through shoots arising from its creeping black roots. Roots of one plant can cover 14 square yards, and penetrate 23 feet deep within 2 growing seasons. Stems are 18 to 36 inches tall with pink or lavender flowers. russian knapweed flowersA single Russian knapweed plant can produce 1,200 seeds per year but reproduction is mainly through shoots arising from its spreading roots. Several allelopathic compounds have been found in Russian knapweed that can inhibit other plants. Russian knapweed is generally avoided by grazing animals due to its bitter taste, and too much ingestion of Russian knapweed by horses causes a fatal neurological disorder.

Why is Russian knapweed a problem in the Great Basin?
Russian knapweed can grow at relatively cool temperatures when soil moisture is usually most plentiful. Russian knapweed does not colonize new sites easily but once established is highly competitive and spreads aggressively to form dense, single-species stands that can persist indefinitely. Russian knapweed is a community-altering invader, reducing forage for livestock and biodiversity for wildlife habitat.


How can we fight this weed?Russian knapweed plant
Russian knapweed does not readily establish in healthy, natural habitats, so maintaining healthy communities and monitoring regularly is the best defense. Once established, managers should stress the plant (biological or herbicide control) and cause it to use up nutrient reserves in its roots, eliminating new seed production (cutting), and controlling vegetative spread by isolating the infestation so no root fragments are transported to other locations. Even following these steps, Russian knapweed has proven more difficult than other knapweed species to control. Herbicide control can be successful on small scales. Refer to the Weed Management Handbook on the University of Wyoming Extension website for up-to-date herbicide information.

Images:
-Drawing: Michael B. Piep © 2006.
-Flower: Eric Coombs, Oregon Department of Agriculture, (http://www.forestryimages.org, 26 September 2006).
-Plant: Steve Schoenig CDFA.

Text references:
-University of Nevada Reno. Cooperative Extention. Fact sheet 04-37, Managing Russian Knapweed. Available: (http://www.unce.unr.edu/publications/FS04/FS0437.pdf, 27 September 2006)
-USDA, NRCS. 2006. The PLANTS Database (http://plants.usda.gov, 26 September 2006). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
-Whitson, T. D., et.al. 2000. Weeds of the West., 9th ed. Western Society of Weed Science, Newark, CA.
-Zouhar, Kris 200 1. Acroptilon repens. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).