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Russian Knapweed <br />Page 2 of 3 <br />alielopathy (biochemicals it produces that inhibit the growth of other plants). A 2002 <br />survey conducted by the Colorado Department of Agriculture showed Colorado with more <br />than 118,341 infested acres of Russian knapweed. Russian knapweed is toxic to horses. <br />Phenology, Biology and Occurrence <br />Russian knapweed emerges in early spring, bolts in May to Lune {elevation dependent) <br />and flowers through the summer into fall. It produces seeds sparingly, approximately 50 <br />to 500 per shoot. Seeds are viable for two to three years in soil. Its primary method of <br />reproduction is from vegetative propagation, with seed of secondary importance. Roots <br />from a recently established plant expand rapidly and may cover up to 12 square yards in <br />two growing seasons. <br />Russian knapweed is native to southern Ukraine, southeast Russia, Iran, Kazakhstan and <br />Mongolia. It grows on clay, sandy or rocky prairies and sunny meadows; on saline soils; <br />or clay, rocky or sandy shores of lakes and rivers; and on rocky and clay slopes of hills <br />and bottomiands. It is a weed of cultivated land, dry pastures and degraded noncropland <br />(waste places) in its native land. Russian knapweed grows in most western states. In <br />Washington, it is common on heavier, often saline soils of bottomiands and grows in <br />pastures, hayfields, grainflekis and irrigation ditches. In Colorado, Russian knapweed is <br />not restricted to certain soils and occurs in pastures, agronomic Crops, roadsides, waste <br />places and rangeland. Stands may survive 75 years or longer. <br />Management <br />like other creeping perennials, the key to Russian knapweed control is to stress the weed <br />and cause it to expend nutrient stores in its root system. An integrated management <br />plan should be developed that places continual stress on the weed. Currently, the best <br />management plan includes cultural control combined with mechanical and/or chemical <br />control techniques. A single control strategy, such as mowing or a herbicide, usually is <br />not sufficient. <br />Russian knapweed typically invades degraded areas, dominating the plank community <br />and desirable plants (e.g. perennial grasses). Seeding competitive, perennial grass <br />species (cultural control) after Russian Imapweed has been stressed by other control <br />measures (set-up treatments) is essential. Set-up treatments may include chemical or <br />mechanical methods. <br />Cooperative research between Colorado State University and the University of Wyoming <br />showed that chemical set-up treatments were superior to mowing. Curtail (clopyralid + <br />2,4-D), Escort (metsulfuron), and Roundup (glyphosate) were used to suppress Russian <br />knapweed. Then perennial grasses were sown in late fall as a dormant seeding. Tillage is <br />necessary to overcome the residual alleiopathic effects of Russian knapweed. Curtail (3 <br />quarts per acre) (A) or Escort (1 ounce/A) were applied at the bud-growth stage. <br />Roundup was applied twice at 1 quart/A, first at the bud-growth stage and again about 8 <br />weeks later. Curtail controlled Russian knapweed best, but Roundup failed to control it. <br />None of the herbicides injured seeded grasses. Grasses established similarly among <br />herbicide suppression treatments, even though Russian knapweed control varied. <br />However, where Escort or Roundup was used to suppress Russian knapweed, additional <br />herbicide treatments would be necessary to achieve acceptable control. <br />While two mowings, eight weeks apart (first at bud-growth stage), suppressed Russian <br />knapweed during that year, the weed recovered vigorously the subsequent season. <br />Perennial grasses established in the mowing treatments but much Tess than in herbicide <br />treatments. Two mowings per year for several years may control Russian knapweed <br />better, but further research is needed to test this hypothesis. Currently, no biological <br />control is available for this weed. <br />Chemical control. In most circumstances, an herbicide alone will not effectively manage <br />Russian knapweed. However, there may be situations where desirable plants within a <br />Russian knapweed infestation may compete effectively with the weed if it is stressed with <br />http://www.exf.colostate.edu/pubs/natres/03111.htm1 6/20/2005 <br />