2012-10-29_PERMIT FILE - M2012045 (6)

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While mowing twice, eight weeks apart (first at bud -growth stage), suppressed Russian knapweed during that year, the weed recovered vigorously the subsequent season. Perennial grasses established in the mowing treatments but much less than in herbicide treatments. Mowing twice per year for several years may control Russian knapweed better, but further research is needed to test this hypothesis. Currently, no biological control is available for this weed. Chemical Control of Russian Knapweed In most circumstances, an herbicide alone will not effectively manage Russian knapweed. However, there may be situations where desirable plants within a Russian knapweed infestation may compete effectively with the weed if it is stressed with a single weed management technique. When integrating chemical and cultural control, avoid using herbicide rates that injure grasses because of active 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 control 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 (ddorsilfuron), 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. Mechanical Control of Russian Knapweed 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, thicksprlce wheatgrass, crested wheatgrass and Russian wildrye established after Russian knapweed was suppressed with herbicides. Sod - forming perennial grasses, hike streambank or thickspike wheatgrasses, help prevent reinvasion better than bunch grasses Lire crested wheatgrass. lithe Russian knapweed stand is not too old and grasses are still present, stimulating grass growth by irrigation (where possible) should increase grass competition with knapweed and keep the weed under continual stress. Spotted knapweed