Sequential Pyroxasulfone Applications with Fluxofenim Reduce Sorghum Injury and Increase Weed Control

Abstract

Core Ideas Selective control of weedy grasses is difficult in grain sorghum due to the presence of wild relatives. Pyroxasulfone provided greater weed control than S‐metolachlor but caused more crop injury. Sorghum protection from pyroxasulfone provided by fluxofenim was dependent on the environment. Split applications of pyroxasulfone equal to the highest single rate provided similar weed control. Controlling weeds selectively is a challenge when producing grain sorghum [Sorghum bicolor (L.) Moench]. Pyroxasulfone, a preemergence (PRE) herbicide, has demonstrated excellent grass and broadleaf control in maize (Zea mays L.) and soybean [Glycine max (L.) Merr]. However, pyroxasulfone is not labeled for grain sorghum because crop injury is a major limitation. Our first objective was to evaluate five herbicide safeners in the greenhouse to determine their ability to protect sorghum from pyroxasulfone. Growth data indicated seed‐applied fluxofenim provided the highest level of protection to emerging seedlings. A second objective was to evaluate fluxofenim for protecting sorghum from single and sequential pyroxasulfone applications in the field. A split‐plot in a randomized complete block design evaluated six pyroxasulfone (whole plot) and two fluxofenim treatments (subplot) in 2015 and 2016. A single PRE treatment of S‐metolachlor, an untreated‐weedy control, and weed‐free control were compared with pyroxasulfone to assess weed control, crop injury and stand count, and grain yield. Pyroxasulfone provided greater weed control than S‐metolachlor. However, as pyroxasulfone rates increased both weed control and crop injury increased, regardless of safener. In contrast, sequential pyroxasulfone applications (90/120 or 120/90 g ai ha−1) did not elicit as much crop injury or stand reductions as a single PRE application at the same total rate (210 g ai ha−1) and maintained weed control, which resulted in higher yields. Despite increased crop tolerance and yield with sequential relative to single pyroxasulfone applications, these findings indicate a more effective herbicide safener for pyroxasulfone in grain sorghum is required.