Reduced tillage farming systems are currently being used to decrease production costs and soil erosion on the Texas Southern High Plains. Adequate weed control is essential for a successful reduced tillage farming system. Current herbicide programs, which include the use of a preplant incorporated treatment, must be modified to obtain weed control without disturbing existing crop residues.

Studies were conducted during the 1986 growing season at the Texas Agricultural Experiment Station near Lubbock, Texas to determine the effect of various crop residues on the efficacy and persistence of several preemergence herbicide treatments in cotton. Treatments included 0.75X, 1.0X, and 1.25X of normal use rates of metolachlor, methazole, diuron, dipropetryn, and prometryn. Herbicide treatments were applied preemergence using a tractor-mounted, compressed-air plot sprayer calibrated to deliver 140 1/ha. Cotton was planted in existing cotton and sorghum stalks in no till and in conventional till systems. In addition, wheat was planted in the no till cotton stalks and subsequently terminated to supply additional crop residue. Good mid-season pigweed control ( > 80% ) was achieved with a]l treatments in the conventional till plots and in the no till plots containing cotton stalk-wheat stubble residue. Higher rates of metolachlor, methazole, and diuron were required to control pigweed in the cotton planted in the sorghum stalk residue. Cotton injury was present with some treatments and the overall trend was greater injury in the conventional till plots as compared to the no till plots. Cotton yields were similar across tillage systems and reflected the pigweed control attained with various herbicide treatments.