Seletividade de sistemas de controle químico de plantas daninhas na cultura do algodoeiro

Abstract

Since herbicide selectivity may be affected by the combined use of two or more molecules, it is fundamental to carry out studres intended to evaluate the selectivity of herbicide mixtures on cotton, in different application modalities. In this context, the aim of this study was to evaluate the selectivity of herbicides applied alone or in tank mixtures, post in different modalities (pre-emergence - PRÉ, "over the top" and post emergence - POST) on cotton under the Brazilian savanna condition. Eight experiments were conducted in Luís Eduardo Magalhães-BA, in a soil with 13% clay, four of them in 2008/2009, two in 2009/2010 and two in the 2010/2011 season. The cultivars used were Delta Opal, FMT 701 IMA and LL 6001. All assays were performed using two-fold checks. All herbicide treatments were always kept free of weeds throughout the cycle. The herbicides alachlor, metolachlor and S-oxyfluorfen applied PRE, resulted, on several occasions, in yield losses and are considered the most risky in those conditions. S-metolachlor applied "over the top", was in most experiments, selective to cotton, suggesting that there might be a difference in herbicide selectivity depending on their modality of application. There is difference in susceptibility between cultivars, and cv. FMT 701 was the most sensitive to herbicide treatments evaluated. Pyrithiobac-sodium can be safely used on LL cotton crop, in mixture with ammonium-glufosinate in the first application in POST. Two applications of pyrithiobac-sodium-sodium + trifloxysulfuron in POST, resulted in several occasions, in decreases in cotton yield. Both diuron and prometryne can be safely used in pre-emergence of cotton. Triple mixtures caused, on several occasions, yield losses. There might be increases in crop injury by mixing three distinct modes of action. A recommendation with a higher level of security would be to use mixtures of two herbicides (trifluralin and clomazone in mixture with diuron or prometryne) in PRE (without the presence of alachlor, metolachlor or S-oxyfluorfen) plus S-metolachlor in "over the top ". For non-genetically modified varieties, a single application of pyrithiobac + trifloxysulfuron-sodium can be used with safety. For LL cotton can be used up three applications of glufosinate ammonium alone, or two applications of glufosinate ammonium even mixed with pyrithiobac-sodium in the first application.