Preemergence applied herbicides were evaluated for cotton injury potential and large crabgrass, Digitaria sanguinalis (L.) Scop., control in field trials located at Belle Mina, Prattville, and Headland, Alabama in 1992 and 1993. Treatments included a untreated check, Command 4E (clomazone), Zorial 80DF (norflurazon), and Prowl 4E (pendimethalin), each applied at l.0 lbs. active/acre, Dual 8E (metolachlor) applied at 1.0, 1.25, and 1.5 lbs. active/acre, and MON 13200 (thiazopyr) applied at 0.2 and 0.38 lbs. active/acre. Treatments were applied immediately after planting either alone or tank-mixed with Cotoran 4L (fluometuron) at 2.0 lbs active/acre. All trials were planted into standing wheat which had been killed approximately 3 wks before planting using 1.5 lbs glyphosate/acre. Disulfoton at 0.75 lbs. active/acre was used in-furrow with all trials to safen cotton to Command herbicide. The trial at Belle Mina in 1993 was dropped due to carryover from an experimental herbicide used the previous year.

Average cotton stand counts from five trials obtained when most plants were in the two-leaf stage showed Command, Zorial, Prowl, and both rates of MON 13200 were equal to the untreated check (105 plants/30 ft row). Dual decreased stand counts, providing 91, 83, and 81 plants/30 ft of row for rates of 1.0, 1.25, and 1.5 lbs per acre, respectively. Cotton injury was also greatest with Dual treatments, ranging from 16 to 20% from the lowest to highest rate (where 0 = no injury and 100 = death).

Large crabgrass control in early season (mid May) was excellent (>90%) and equal for all preemergence treatments when combined with fluometuron. Command, Prowl, Zorial, and both rates of MON 13200 provided excellent control in early season without fluometuron. Late-season (mid July) control was good (>80%) for all treatments when combined with fluometuron. Fluometuron alone provided 63% control late season. Command, Prowl, and both MON 13200 treatments provided greater than 80% control in late season. Zorial provided 78% and Dual provided 63 to 69% control for rates of 1.0 to 1.5 lb/acre, respectively in late season. A high population of Palmer pigweed, Amaranthus palmeri S. Wats., infested the trial site at Headland. Late-season control in 1992 was <74% with all treatments except Zorial combined with fluometuron (85%). Late-season Palmer pigweed control in 1993 was fair (>70%) for all treatments except Command (63%) and the low rate of MON 13200 (52%) applied alone. All preemergence treatments mixed with fluometuron provided >80% pigweed control in 1993. Average seed cotton yields were equal for all preemergence treatments when mixed with fluometuron (2204 to 2424 lbs/acre). Without fluometuron, Prowl and MON 13200 at 0.38 lb/acre provided yields higher than Dual at all rates. The untreated check averaged 1370 lbs/acre.