AN INNOVATIVE METHOD TO EVALUATE THE IMPACT OF TEMPERATURE ON IODOSULFURON-METHYL SELECTIVITY TO OAT CROP

Temperature affects the selectivity of post-emergence herbicides in a complex manner. The objective of this work was to develop a method to estimate the impact of temperature on herbicide selectivity using the white oat (Avena sativa) crop and iodosulfuron-methyl as study models. Greenhouse/growth-chamber experiments were conducted using a completely randomized design with the treatments arranged as a bi-factorial, with three repetitions. The first factor consisted of six temperatures (10, 15, 20, 24, 28 and 32 degrees C) to which the plants were submitted during one week after the herbicide spray. The second factor corresponded to seven doses of iodosulfuron-methyl (0, 0.2, 0.4, 0.8, 1.2, 5 and 20 g ha(-1)). For each temperature, regression curves were fitted to the dose-response data. The rate of herbicide efficacy was computed through the method first proposed in this study. The crop tolerance to the herbicide increased proportionally to the temperature, suggesting the product detoxification is improving crop selectivity. In practical terms, it is predicted that white oat crop tolerance to iodosulfuron-methyl increases in regions of the world with high temperatures. The method developed here also can be used to understand the effect of temperature on herbicide efficacy on weeds.