| Field studies were conducted to evaluate the effects of low levels of atrazine, fluometuron, imazaquin, and norflurazon on the growth and yield of corn, cotton, grain sorghum, rice, soybeans, and wheat. Corn, grain sorghum, and rice injury occurred and yields were reduced when norflurazon concentrations were 450, 450, and 710 ng/g soil or greater. Corn, cotton, and wheat heights and yields were reduced when imazaquin concentrations were 13 ng/g, 13 ng/g, and 45 ng/g soil, respectively for crops. Imazaquin concentrations ranging from 0.007 to 0.024 ug/g and 0.00 to 0.015 ug/g were found in soil samples taken 12 and 24 months, respectively, following preplant-incorporated applications at rates of 140 g/ha. Imazaquin persistence was greater in clay soils than loams or sandy loams. Cotton and soybeans were injured and yields were reduced with atrazine at 200 ng/g. Wheat was injured and yields were reduced with atrazine concentrations of 100 ng/g. Rice heights and yields were reduced by metolachlor at 300 ng/g or greater.;Leaching, dissipation, and efficacy of metolachlor and imazaquin were evaluated in field studies when the herbicides were applied by conventional and chemigation methods to a silt loam soil. Laboratory studies were conducted to evaluate adsorption and mobility of the herbicides in five soil depths. In the field, imazaquin leaching to a depth of 8 to 15 cm was observed following application by chemigation; however, leaching below 22 cm did not occur. Metolachlor leaching below 30 cm was not observed for either application method. Dissipation of imazaquin was increased when the herbicide was applied by chemigation. In the laboratory, imazaquin sorption was greatest in the 30- to 38-cm soil depth with a pH of 4.9. Metolachlor sorption was highest in the 0- to 8-cm soil depth of a silt loam soil with an organic matter content of 1.1%. Efficacy of the herbicides was not affected by method of application. |
