Bean (Phaseolus vulgaris L.) response and weed control efficacy of pre-plant-incorporated of pendimethalin

Common bean (Phaseolus vulgaris L.) is an important legume crop in Israel and heavily relies on S-metolachlor for weed control. Pre-emergence (PRE) treatment of pendimethalin can also be used for this crop, however, such application results with suboptimal weed control results. This study aimed to evaluate crop safety and weed control efficacy of pendimethalin applied by pre-plant soil incorporation (PPI) in bean. Three field experiments were conducted between 2015 and 2020, in which pendimethalin (182 g ai ha(-1)) was applied PRE and PPI with and without PRE S-metolachlor (120 g ai ha(-1)). In the 2019 and 2020 experiments, PPI pendimethalin, both with and without S-metolachlor, was safe, with no plant injury or pod weight reductions recorded. In the 2015 experiment, reduced crop development was observed 35 days after sowing for both PPI pendimethalin treatments. Furthermore, pod weight was similar to 25% lower in these PPI treatments compared to the commercial treatment of S-metolachlor alone. When the pendimethalin + S-metolachlor treatment was compared to the commercial control, significant differences were observed (p = 0.0.0356). The main reason for the differences between the 2015 and the 2019/2020 experiments was ascribed to the seeding dates (March vs. August) and the lower temperatures in March, which may have prolonged pendimethalin half-life in the soil and its phytotoxicity. In terms of weed control, the PPI pendimethalin treatments were favorable over the PRE treatments for the control of prostrate pigweed (Amaranthus blitoides S. Watson), and in the control of wheat (Triticum aestivum L.) self-seeding grains. The presented results demonstrate that pendimethalin applied PPI can be safely integrated into bean weed control programs, to improve weed control. However, to ensure maximal crop-safety, application during warmer periods is recommended.