Performance of herbicides used in cotton for control of Amaranthus

Abstract

Some species of Amaranthus are widely distributed in cotton crops. In recent years, ineffective weed control after herbicide use of some species has been reported. The current study was installed in order to find effective alternatives to a proper management of these species. Two simultaneous experiments were carried out for each species in this study (Amaranthus lividus and Amaranthus hybridus), and in each of them, a different stage of weed development (2 to 4 and 4 to 6 leaves) was focused. Twenty two herbicide combinations were arranged in a completely randomized design with four replicates for each experiment. Treatments were composed by the single or combined application of pyrithiobac-sodium, ammonium-glufosinate, glyphosate and trifloxysulfuron-sodium at different doses. For pyrithiobac, the best weed control results for both A. lividus and hybridus were found with applications of doses ³ 28 g ha^-1. Glufosinate and glyphosate presented excellent control of both Amaranthus species, despite doses or stages of application. Comparing the use of single herbicides and tank mixtures, trifloxysulfuron+pyrithiobac resulted in improved weed control only for early applications. No negative effects of Amaranthus species were observed for mixtures of glyphosate and pyrithiobac. Mixtures of pyrithiobac and glufosinate increased A. lividus and A. hybridus control levels.