Seletividade de herbicidas aplicados em isolado ou associados na cultura do milho

Abstract

Among the strategies used to control weeds in corn fields, the chemical method is the most used by farmers because it is efficient, practical, and cheaper compared to other available options. Therefore, this study aims to evaluate the selectivity of herbicides applied alone or combination of the hybrid FS 400 PW. Experiments were repeated for two agricultural seasons (2020/21 and 2021/22) using a randomized block design with four repetitions. The treatments applied post-emergence they were: ammonium glufosinate (400 g ha-1), mesotrione + atrazine (120 + 1200 g ha-1), 2,4-D amine (1209 g ha-1), dicamba (720 g ha-1) and 2,4-D coline (2005.86 g ha-1). These treatments were applied alone or in combination in the tank mix, with two additional controls, one weeded and one infested. To the 7, 14, 21, 28, and 35 days after the treatments were applied (DAT) the phytotoxicity of the herbicides to the corn he was evaluated. The physiological characteristics of the corn were measured at 21 days after treatment (DAT) for the 2020/21 season and at 27 DAT for the 2021/22 season. At the corn harvest, yield components (ear length, weight of 1000 grains, and grain productivity) were determined. The herbicides that showed the highest phytotoxicity to the corn were ammonium-glufosinate + 2,4-D amine, ammonium-glufosinate + 2,4-D choline, and mesotrione + atrazine + 2,4-D choline applied in a tank mix. The use of ammonium-glufosinate alone and mesotrione + atrazine showed the lowest phytotoxicity to the hybrid corn FS 400 PW. The herbicides 2,4-D amine, dicamba, and 2,4-D choline combined with ammonium-glufosinate and with mesotrione + atrazine increased the phytotoxicity levels to the hybrid corn FS 400 PW. The combination of ammonium-glufosinate, mesotrione, and atrazine showed the best performance for all evaluated physiological variables: internal CO2 concentration (Ci), transpiration rate (E), stomatal conductance of water vapor (GS), photosynthetic rate (A), water use efficiency (WUE), and carboxylation efficiency (CE) compared to the other treatments. The use of ammonium-glufosinate alone demonstrated better performance in corn yield components (ear length, weight of 1000 grains, and grain productivity), statistically equaling the weeded control. The weeded control and ammonium-glufosinate showed an average increase in corn grain productivity of 2.58 and 2.27 t ha-1 or 86.72% and 76.40%, respectively, compared to the unweeded control. The use of herbicides in isolation causes less phytotoxicity to hybrid corn FS 400 PW than applications in mixtures in a tank mix and, consequently, there is greater grain productivity.