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the Russian knapweed stand is not too old and grasses are still present, stimulating grass <br />growth by irrigation (where possible) should facilitate the competitive edge of the grasses and <br />provide additional stress to the weed. Depending on the moisture regime, nitrogen fertilizer ap- <br />plied in conjunction with an herbicide (see Section 3.3 below) significantly improves the compe- <br />titiveness of residual grasses. <br />Livestock such as cattle, sheep, and goats will graze Russian knapweed and remove its above- <br />ground biomass. This approach has a negligible effect on the vigor and viability of the root sys- <br />tem unless the grazing is repeated whenever green leaves emerge, and desirable plants will <br />become stressed if grazing is heavy. Therefore, if grazing is attempted for Russian knapweed <br />control, caution must be taken to avoid overgrazing desirable plants while sufficiently grazing <br />the weed. <br />3.3 CHEMICAL CONTROL <br />Herbicides can be used to manage existing stands of Russian knapweed, but repeated treat- <br />ments are required and their effectiveness may be variable over time. Russian knapweed is <br />best controlled when herbicides are applied very late in the growing season and/or following <br />several hard frosts (usually mid-October). At this time in the season the plants will look dormant <br />with grey stems and no leaves, but control should be underway by the following growing sea- <br />son. Application in mid-September or during flowering in mid-summer generally provides short- <br />er-term control. See Table 1 for herbicide suggestions.4 <br />Under most circumstances, herbicide use without the additional use of desirable competitive <br />plant species will not effectively manage Russian knapweed. When integrating chemical and <br />cultural control, avoid using herbicides at rates that injure grasses, as this will reduce desirable <br />competition. To maximize success, chemical applications should be combined not only with cul- <br />tural controls, but also with mechanical approaches. <br />For more information on chemical control see: <br />http://www.cooDext.colostate.edu/boulder/AG/agweedsspecificweeds.shtmI . <br />4 Some sources recommend the use of Telaro (chlorsulfuron) to control Russian knapweed, but this is not recom- <br />mended for application on soils with pH >7.5 such as those at Mesita Hill. Chlorsulfuron has an extended soil resi- <br />dual in alkaline soil and will interfere with the establishment of broadleaf crops, forbs, and some grasses sown on the <br />same soils after its application. <br />5