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tural, mechanical, and/or chemical controls. The subsections below describe each of these ap- <br />proaches <br />3.1 MECHANICAL CONTROL <br />Hand-pulling Russian knapweed is very difficult and has limited effectiveness, but may be effec- <br />tive for small infestations during the establishment year. For best results, pull the plants when <br />the soil is wet and before seeds are formed (and always wear gloves). Since Russian knap- <br />weed reproduces primarily from rootstocks, most of the root system must be removed to effec- <br />tively eliminate the plant. Plants with seeds should be bagged and burned or buried in a landfill. <br />Cultivation of Russian knapweed produces broken root fragments that serve as colonizing <br />propagules, although tillage is usually necessary to overcome its residual allelopathic effects <br />Mowing or disking several times a year is expensive and only controls top growth. However, if <br />done frequently, such as every 2 to 3 weeks during the growing season, the new growth will be <br />less vigorous, possibly diminishing or even exhausting the plants' ability to regenerate. This <br />may be particularly successful in conjunction with herbicides applied in the fall. Mowing before <br />seed set will reduce, but not completely eliminate, seed production, since Russian knapweed <br />usually produces seed-bearing, prostrate stems below the height of the mower blade. If mowing <br />is attempted, it should be conducted prior to seed set. <br />Burning Russian knapweed will not provide long-term control because new plants will regener- <br />ate from the rootstocks. Burning is therefore not recommended <br />3.2 CULTURAL CONTROL <br />Absolute cultural control of Russian knapweed by manipulating soil moisture and fertility, graz- <br />ing, or sowing competitive species is very difficult. Furthermore, it is extremely difficult to estab- <br />lish perennial grasses in dense stands of Russian knapweed due to allelopathic chemicals <br />produced by the knapweed. Most effective is to control the weed by mechanical, chemical, or <br />biological means, and then to plant desirable vegetative species. <br />If initial control of Russian knapweed is not followed by planting desirable species, it and/or <br />other weeds will colonize the area. Sod-forming perennial grasses, like streambank or thick- <br />spike wheatgrasses, help prevent reinvasion better than bunch grasses like crested wheatgrass. <br />4 <br />