Control of Conyza bonariensis resistant biotypes with glyphosate + chlorimuron-ethyl as a function of development stage

Abstract

Desiccation is considered the initial crops management and one of the most important practices for soybean deployment in no-tillage system. After starting the cultivation of transgenic soybean, the use of glyphosate in this crop increased expressively and provided Conyza bonariensis selection resistant to this herbicide. This study aimed to evaluate the efficacy of glyphosate in association with chlorimuron-ethyl in controlling glyphosate-resistant C. bonariensis, at different growth development stages. Eight treatments were constituted by the associated use of 2.5 L ha^-1 of glyphosate (1250 g a.e.ha^{- 1}) and 60 g ha^-1 (15 g a.i. ha^{- 1}) of chlorimuron - ethyl in plants with 3 leaves, 4 to 6 leaves, 6 to 9 leaves, 10 to 13 leaves, 13 to 16 leaves, 20 leaves, in flowering stage and a control without application. Experimental design was a randomized block with six replications. Visual control evaluations were performed at 7, 15 and 21 days after application (DAA), also determining leaves dry mass. Excellent control was found by using the association of glyphosate + chlorimuron-ethyl at plants < 9 leaves.