Selectivity of associations and rates of the herbicides in wheat post emergence

Abstract

The main weeds in wheat are wild radish and ryegrass, and its post-emergence control is based on herbicides inhibiting the enzyme acetolactate synthase (ALS) and acetyl coenzyme A carboxase (ACCase), which as a function of resistance limits the control options. Herbicide combinations have been used for post-emergence of wheat; however, the effects of herbicidal combinations are poorly understood. The objective of this work was to evaluate the selectivity of wheat to herbicide associations and rates applied in post-emergence. Three field experiments were carried out in a no tillage system, in a randomized complete block design with three replicates. The experiments were conducted in Santa Bárbara do Sul-RS, Cruz Alta-RS and Tupanciretã-RS. Rates and associations between the 2,4-D herbicides, metsulfuron-methyl, iodosulfuron, pyroxsulam and saflufenacil applied in wheat tillering were studied. The evaluated variables were phytotoxicity at seven, 14, 21 and 35 days after application (DAA), yield (kg ha-1) and hectoliter weigh (HW). The data were analyzed together. At 35 DAA, the highest phytotoxicities were observed for metsulfuron methyl at the dose of 9 g a.i. ha-1 and for saflufenacil associated with metsulfuron methyl. The results of yield demonstrate that the association between 2,4-D and metsulfuron-methyl, saflufenacil isolated or associated with metsulfuron-methyl, and iodosulfuron are selective for wheat. Metsulfuron methyl at rates of 6 and 9 g a.i. ha-1 and pyroxsulam caused a significant reduction in wheat yield and were not considered selective. However, the hectoliter weight of the grains was not influenced by herbicides used of this study.