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