PERMFILE128898 - Laserfiche WebLink

Home Browse Search

N A T U R A L R E S O U R C E S~ S E R I E S Quick Facts... 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. Urtiversity® ®Colorado State University Cooperative Extension. 9/98. Revised 3/03. www. ext.colostate.edu RANGE Russian Knapweed no. 3.111 by K.G. Beck' Russian knapweed (Acroptilon repens) is a creeping, herbaceous perennial of foreign origin [hat 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 solitary, urn-shaped flower heads occur on shoot tips and generally aze 1/4 to 1/2 inch in diameter with 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. The weed forms dense, single species stands over time due to competition and allelopathy (biochemicals i[ produces that inhibit the growth of other plants). A 2002 survey conducted by the Colorado Department of Agriculture showed Colorado with more than 118,341 infested acres of Russian knapweed. Russian knapweed is toxic to horses. Phenology, Biology and Occurrence Russian knapweed emerges in early spring, bolts in May to June (elevation dependent) and flowers through the summer into fall. It produces seeds sparingly, approximately 50 to 500 per shoot. Seeds are viable for two to three years in soil. Its primary method of reproduction is from vegetative propagation, with seed of secondary importance. Roots from a recently established 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 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 noncropland (waste places) in its native land. Russian knapweed grows in most western states. In Washington, it is common on heavier, often saline soils of bottonilands 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.