Weed Management in Transplanted Lettuce with Pendimethalin andS-Metolachlor

Abstract

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.