Snap Bean (Phaseolus vulgaris L.) Response to Postemergence Herbicides at Different Growth Stages

Weeds competing with snap beans can reduce harvest efficiency and lower yields. Postemergence herbicides are most effective when applied to small weed seedlings, but their application timing must also account for crop development to avoid injury. Achieving a balance between effective weed control and crop safety can be challenging, especially if crop emergence is uneven. In 2021, field experiments were conducted in Delaware, Pennsylvania, and New York, USA, to evaluate crop response to bentazon (0.84 kg a.i./ha), fomesafen (0.21 kg a.i./ha), and bentazon plus fomesafen or imazamox (0.04 kg a.i./ha) when applied postemergence at the cotyledon, unifoliate, and first trifoliate snap bean growth stages. Snap bean injury was greatest in herbicide treatments containing bentazon plus fomesafen (10%–34%). Averaged across herbicides, applications at the trifoliate stage were the least injurious to snap beans. Crop yield was most affected by the bentazon plus fomesafen and imazamox treatments (77% and 76% of untreated control, respectively), and by applications at the cotyledon stage (78% of untreated control). Results highlight that applications of postemergence herbicides should adhere to label guidelines (i.e., treatment after the first trifoliate leaf is fully expanded) to ensure crop safety and maximize yields.