Weed Management in Transplanted Lettuce with Pendimethalin andS-Metolachlor

Few herbicides are available for use in lettuce and hand weeding is required for commercially acceptable weed control. More effective herbicides are needed. Here field evaluations of pendimethalin andS-metolachlor for weed control in transplanted lettuce are reported. Pendimethalin was evaluated PRE at rates between 0.6 and 6.7 kg ai ha−1, and POST at 1.1 and 2.2 kg ha−1. Both pendimethalin PRE and POST applications were safe to transplanted lettuce and provided similar weed control. Pendimethalin PRE at rates of 1.1 kg ha−1and higher provided better weed control than the industry standard, pronamide at 1.3 kg ha−1.S-Metolachlor PRE was evaluated at rates between 0.6 and 5.6 kg ha−1.S-Metolachlor at rates up to 2.8 kg ha−1caused little or no crop injury or yield reduction in transplanted lettuce, andS-metolachlor at rates of 1.4 kg ha−1and higher improved weed control compared with pronamide at 1.3 kg ha−1. Pendimethalin andS-metolachlor are not labeled for transplanted lettuce, but we suggest that labeling be pursued at rates of 1.1 and 0.7 kg ha−1, respectively. Pendimethalin at 1.1 kg ha−1applied PRE or POST improved weed control by 57 and 42%, respectively compared with pronamide.S-Metolachlor PRE at 0.7 kg ha−1was less effective on weeds than pendimethalin, but maintained weed control level similar to pronamide. Pendimethalin andS-metolachlor have potential for use in transplanted lettuce production and provide alternatives to current transplanted lettuce herbicides.