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Russian Knapweed Page 3 a single weed management technique. When integrating chemical and cultural control, avoid using herbicide rates that injure grasses because effective competition will•be reduced. Russian knapweed is controlled with Tordon 22K (picloram) at 1 to 2 quarts/A. Tordon may be broadcast sprayed up to 1 quart/A or spot sprayed at rates up to 2 quarts/A. Tordon plus 2,4-D (1 to 1,5 pints + 1 quart/A) also will centrol Russian knapweed. If low rates of Tordon or Tordon plus 2,4-D are used, application for two consecutive years may be necessary to achieve adequate control. Apply Tordon any time the weed is actively growing. For Telar (chlorsulfuron), a noncrop herbicide that controls Russian knapweed, application timing is critical. Apply {1 ounce/A) when Russian knapweed is in the bloom to postbloom stage. Earlier applications do not control the weed effectively. Fall is a good time to apply Telar, but It may injure smooth brome or other brome species. Always add a good agricultural surfactant at 0.25 to 0.5 percent v/v to the spray solution. Escort (metsulfuron) is labeled for pasture and rangeland use. Apply it at 0.75 to 1 ounce/A with a good agricultural surfactant. Optimum timing for Escort is similar to Telar. Cultural control. Russian knapweed tends to form monocultures and usually eliminates other plants. Therefore, sowing desirable plant species is necessary after the weed is controlled. Smooth brome will compete with Russian knapweed. Research shows that streambank wheatgrass, thickspike wheatgrass, crested wheatgrass and Russian wildrye established after Russian knapweed was suppressed with herbicides. Sod-forming perennial grasses, like streambank or thickspike wheatgrasses, help prevent reinvasion better than bunch grasses like crested wheatgrass. If the Russian knapweed stand is not too old and grasses are still present, stimulating grass growth by irrigation (where possible) should increase grass wmpetition with knapweed and keep the weed under continual stress. 1 Colorado State University Cooperative Extension weed specialist and professor, bioagricultural sciences and pest management. 9/98. Revised 3/03. Go to t~ of thi~age• Updated Monday, August 23, 2004. AnswerLink ~ CSU AaNews I Emolovment I Other Links I Publications I Staff Resources ~ Site Search CE Home i CSU Home I RamPoint I About Us ~ Calendar I Staff Directarv I Webmaster Disclaimer I Eaual Opoortuniiy INon-Discrimination Statement http://www.ext.colostate.edu/pubs/natres/03111.htm1 6/20/2005