Influence of the Time of Day of Application on the Efficacy of Ammonium Glufosinate Formulations

The timing of ammonium glufosinate application influences its efficacy in the preharvest desiccation of soybean. The objective of this study was to evaluate the performance of two glufosinate‐ammonium formulations applied at different times of the day for the preharvest desiccation of soybeans and to assess their physiological impacts on the crop. Two experiments were conducted, one for each formulation (Finale and Trunfo), in a randomized complete block design with four replications. The treatments consisted of applications at the following times: 6:20 a.m., 10:20 a.m., 2:20 p.m., 6:20 p.m., 10:20 p.m. and 2:20 a.m. The following parameters were assessed: defoliation, desiccation, quantification of green pixels, membrane damage, initial fluorescence ( F 0 ), electron transport rate (ETR), ammonia (NH 3 ) accumulation, activity of antioxidant enzymes (peroxidase and superoxide dismutase), daily grain moisture, yield, and thousand‐grain weight. For Finale, the highest defoliation rates (90%) were achieved with applications at 6:20 a.m. and 10:20 a.m., whereas for Trunfo, the highest rates (85%) were achieved at 6:20 a.m., 10:20 a.m. and 2:20 p.m. The greatest reduction in green pixels occurred with applications at 6:20 a.m. and 10:20 a.m., resulting in 95% and 100% decreases in green area, respectively. For both formulations, the greatest membrane damage (60 µs/cm) was observed with the 10:20 a.m. application. The ETR reached 25 and 55 μmol for Finale and Trunfo, respectively. Significant antioxidant enzyme activity was observed for the 6:20 a.m. and 10:20 a.m. treatments, while the highest ammonia (NH 3 ) accumulation occurred at 6:20 p.m. Finale exhibited greater efficacy under high‐light conditions. The Trunfo performed better under low‐light conditions.