Tolerance of Soybeans and Grain Sorghum to Fluometuron Residue

Failure to obtain a stand of cotton (Gossypium hirsutum L.) is often a problem. Cotton can be replanted only during a narrow range of recommended planting dates; therefore, alternative crops are sometimes necessary. The selection of an alternate crop is dependent on the herbicides already applied for preemergence weed control in cotton. Fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea] is a widely used cotton herbicide, which may injure any alternative crop. The objective of this 1973 study was to determine the susceptibility of soybeans [Glycine Max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench.] to fluometuron residues when grown as alternative crops to cotton on a Memphis silt loam at Milan, Tennessee and on a Sequatchie loam at Knoxville, Tennessee. The four main treatments consisted of fluometuron at the rate of 3.36 kg/ha broadcast, 1.68 kg/ha broadcast, 1.68 kg/ha on a treated area basis restricted to a 50 cm band, and no fluometuron. Each main treatment was divided into three sub treatments consisting of three, six, and nine week intervals from date of application to planting. At Milan the 1.68 kg/ha band treatment did not significantly affect the number of live soybean plants, plant height, percent vigor reduction or yield of soybeans at any planting date. Fluometuron treatments of 3.36 and 1.68 kg/ha broadcast required a waiting period of nine weeks before soybeans could be grown without injury. The 1.68 kg/ha band treatment did not cause significant injury or yield reduction of grain sorghum at Milan. Fluometuron treatments of 1.68 and 3.36 kg/ha broadcast required waiting periods of six and nine weeks, respectively, to prevent significant injury and yield reduction of grain sorghum at Milan. Grain sorghum and soybean response and yields and bioassay results showed a decrease in residue with successive planting dates. Grain sorghum exhibited more tolerance to fluometuron residue than did soybeans. Fluometuron did not cause a significant reduction in the number of live plants, plant height, plant vigor or yield of either soybeans or grain sorghum at any rate at Knoxville. Response to fluometuron was obtained in a secondary experiment at Knoxville. Difference in response between locations was primarily attributable to a higher soil organic matter content at Knoxville. Results of oat bioassays showed that fluometuron residues were found primarily in the 0-10 cm depth of soil. Sufficient dissipation had occurred by 24 weeks after application to allow normal growth of oats on all,except the highest rate of fluometuron. Less phytotoxicity, due to fluometuron, was observed on oats grown in treated Sequatchie than in treated Memphis soil.