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10 <br />longed submersion and drainage is minimal. Successful flooding to control these <br />weeds requires continuous submersion from May until September in most cases. <br />Biological Control <br />No natural enemies for use as biological controls are available in the United <br />States at this time. <br />Chemical Control <br />4hitetop species can be controlled using herbicides, although it is difficult. <br />Successful control usually depends on an aggressive reapplication program. On <br />rangeland, roadsides and waste areas apply Escort® (metsulfuron) at ranges from <br />OS to 1 ounce of product per acre to actively growing rosettes early in the spring, <br />to regrowth before bud stage, or to fall regrowth before the first killing frost. <br />Treatment after bloom is generally less effective. It is important to apply this <br />chemical with at least 10 gallons of water per acre and to use a nonionic surfac- <br />tant at a rate of 2 quarts per 100 gallons of solution. Nitrogen fertilization can <br />enhance the vigor of grasses which will slow the rate of re-invasion. <br />Although 2,4-D is somewhat effective, Tordon 22K, a broad spectrum herbicide <br />which provides excellent control of many rangeland weeds, is ineffective on <br />whitetop species. <br />In cereal grains, Ally® applied at %o ounce of product per acre provides reason- <br />able control of whitetop species. Higher rates will injure the crop. These weeds <br />can be effectively controlled in stubble and fallow, but it is important to wait the <br />period stated on the label before planting. <br />There aze no herbicides registered for use on alfalfa, peas and sugar beets that <br />control whitetop. These weeds should be controlled during another part of the <br />crop rotation. <br />