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Scentless Chamomile (Matricaria perforata) Russian knapweed is a member of the Aster family introduced from Europe. It is a creeping perennial that reproduces by seed and creeping, horizontal roots. The ridged stems are stiff and 1 to 3 feet high, with thistle-like flowers that are lavender to white. It is most common in Old Snowmass and the Crystal River Valley. Comments: This weed is very common in Eagle and Garfield counties. At this time, there are very few recorded infestations of Russian knapweed in Pitkin County. Scattered, small patches may be found along State Highway 133 and along Upper Snowmass Creek Road. Like other creeping perennials, the key to Russian knapweed control is to stress the weed and cause it to expend nutrient stores in its root system. An integrated management plan should be developed that places continual stress on the weed. Currently, the best management plan includes cultural control combined with mechanical and/or chemical control techniques. A single control strategy, such as mowing or an herbicide, usually is not sufficient. The plant is toxic to horses, however they must consume it over a period of time before poisoning will occur. Once poisoning occurs horses are unable to chew and advance food to the back of their mouths, swallowing is impaired and horses may drink only if they immerse their head in water far enough to get water to the back of their mouths. Biological control: None currently available. Chemical controls: For additional information contact your local city, county or town natural resource office. (See section VII for phone numbers.) Cultural controls: Russian knapweed tends to form monocultures by eliminating other plants. Therefore, sowing desirable plant species is necessary after the weed is controlled. Research indicates that the native grasses, streambank wheatgrass and thickspike wheatgrass will establish in an area after Russian knapweed is suppressed with herbicides. If the 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 it under continual stress. Locations of Infestation of Russian Knapweed on Roads and Open Space in Pitkin County:
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