Soybean(Glycine max)and Grain Sorghum(Sorghum bicolor)Tolerance to Residues of Tetrafluron and Fluometuron

Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] and tetrafluron {N,N-dimethyl-N′-[3-(1,1,2,2-tetrafluoroethoxy) phenyl] urea} are two urea-type herbicides for weed control in cotton(Gossypium hirsutumL.). In some years, because of cotton stand failure, an alternate crop must be established. Soybeans [Glycine max(L.) Merr.] and grain sorghum [Sorghum bicolor(L.) Moench] are possible alternate crops if they can withstand the residues left from herbicides used for weed control in cotton. Soybeans and grain sorghum were planted 3, 6 and 9 weeks after fluometuron and tetrafluron applications to soil at Knoxville and Milan, Tennessee, in 1975 and 1976. Tetrafluron residues were more toxic to grain sorghum and soybeans than were fluometuron residues. Grain sorghum was less susceptible than soybeans to both herbicides. Grain sorghum was planted 3 weeks after fluometuron (1.7 kg/ha) and tetrafluron (1.7 kg/ha) applications without severe yield reduction. Soybeans were planted in non-treated soil between banded tetrafluron (1.7 kg/ha on a treated area basis), 3 weeks after herbicide application, without significant yield reduction; but when a seedbed was prepared, a 9-week waiting period was required. When soybeans were planted into soil receiving a broadcast application of tetrafluron (1.7 kg/ha), a 9-week waiting period was not sufficient to reduce the residues to a non-toxic level. Soybeans planted 6 and 9 weeks following a broadcast application of fluometuron may or may not sustain yield reduction depending on rainfall frequency and intensity and soil type.