Selectivity of Herbicides Applied Alone or in Tank Mixtures at Different Times of the Day in the Soybean Cultivar DM57i52 IPRO Over Two Growing Seasons
摘要
The application of herbicides, alone or in mixtures, is essential in soybean cultivation, as interactions among chemicals can affect both weed control and crop selectivity. Application timing also matters in these interactions, as sunlight, temperature, and relative humidity vary throughout the day. This study evaluated the selectivity of glyphosate salts, applied alone or mixed with chlorimuron-ethyl, at two times of day, on soybean physiological traits and grain yield components. Experiments were conducted in a randomized block design, in a 7 × 2 + 1 factorial arrangement with four replicates. Factor A consisted of herbicides (chlorimuron-ethyl, glyphosate isopropylamine, ammonium, potassium salts, and their mixtures), and Factor B was application time (6:30 am and 12:30 pm), with a weeded control. Phytotoxicity was assessed 7, 14, 21, 28, 35, and 42 days after treatment (DAT). Physiological traits were measured 28 DAT, and grain yield components at harvest. Chlorimuron-ethyl alone caused the highest visual phytotoxicity, peaking at 32.94%, 7 DAT and declining to 7.67%, 42 DAT. This was reflected in gas exchange, with a 17.1% reduction in photosynthetic rate compared to the control (16.47 vs. 19.86 μmol m⁻2 s⁻1). Mixtures of glyphosate salts with chlorimuron-ethyl showed intermediate phytotoxicity (26.25–27.04%, 7 DAT), higher than glyphosate salts alone (maximum 6.56%, 7 DAT) but lower than chlorimuron-ethyl applied individually. These results highlight the influence of herbicide type, mixture, and application timing on soybean selectivity and physiological responses, providing insights for optimizing post-emergence herbicide strategies.