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r~ A T U R A L R E s 0 ~R C E s ~g S E. R I E s RANGE Russian knapweed is a creeping perennial that reproduces from seed and vegetative root buds. Russian knapweed emerges in early spring, bolts in May to June, and flowers through the summer into fall. Russian knapweed is toxic to horses. The key to Russian knapweed control is to stress the weed and cause it to expend nutrient stores in its root system. The best management plan includes cultural controls combined with mechanical and/ or chemical control techniques. ® Colorado Stale University Cooperative Extension. 9/96. by K. George Beck' Russian knapweed (Acroptilon repens) is a creeping, herbaceous perennial of foreign origin that reproduces from seed and vegetative root buds. Shoots, or stems, are erect (18 to 36 inches tall) with many branches. Lower leaves are 2 to 4 inches long and deeply lobed; upper leaves are smaller, generally with smooth margins, but can be slightly lobed. Shoots and leaves are covered with dense gray hairs. The umshaped flower heads are solitary and occur on shoot tips; generally 1/4 to 1/2 inches in diameter witn smooth papery bracts. Flowers can be pink, lavender or white. Russian knapweed has vertical and horizontal roots that have a brown to black, scaly appearance, especially apparent near the crown. This weed forms dense, single species stands over time due to allelopathy (biochemicals produced by Russian knapweed that inhibit the growth of other plants) and competition. Phenology, Biology and Occurrence Russian knapweed emerges in early spring, bolts in May to June (elevation dependent) and flowers through the summer into fall. Seeds are produced sparingly (approximately 50 to 500 per shoot) and are viable Eor two to three years in soil. Its primary method of reproduction is from vegetative propagation with plants produced from seed being of secondary importance. Roots from a recently established Russian knapweed plant expand rapidly and may cover up to 12 square yards in two growing seasons. Russian knapweed is native to southern Ukraine, southeast Russia, Iran, Kazakhstan, and Mongolia. It grows in these regions on clay, sandy or rocky prairies and sunny meadows, on saline soils, or clay, rocky or sandy shores of lakes and rivers, and on rocky and clay slopes of hills and bottomlands. It is a weed of cultivated land, dry pastures, and degraded non-cropland (waste places) in its native land. Russian knapweed grows in most western states and is toxic to horses. In Washington, it is common on heavier, often saline soils of bottomlands and grows in pastures, hayfields, grainfields and irrigation ditches. In Colorado, Russian knapweed is not restricted to certain soils and occurs in pastures, agronomic crops, roadsides, waste places, and rangeland. Stands may survive 75 years or longer. Management 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 a herbicide, usually is not sufficient. Russian knapweed typically invades degraded areas dominating the plant community and desirable plants (e.g. perennial grasses). Seeding competitive, perennial grass species (cultural control) after Russian knapweed has been stressed Quick Facts...