Glyphosate alone and in association with herbicide for weed control and selectivity in cotton crop RF

Abstract

Cotton (Gossypium hirsutum L.) is a fiber-producing plant that demonstrates high cultivation aptitude in Brazil. However, crop performance is influenced by factors such as weed interference, mainly due to the few options of selective herbicides to be applied in post-emergence in cotton cultivars with RF technology. Thus, the objective of this study was to evaluate the use of glyphosate associated with latifolicides for weed management in cotton crops. For this, a field experiment was carried out, in a randomized block design with 13 tracts and four replications, using cv. Deltapine DP1857B3RF. The treatments were composed of pyrithiobac-sodium at doses (36.4, 42.0 and 50.4 g a.i. ha-1), trifloxysulfuron-sodium (2.25, 2.62 and 3.0 g a.i. ha-1), glyphosate isopropylamine salt and potassium (1,350 and 1,512 g a.i. ha-1) used separately and together, with two deposition formats, in total area and directed jet, and two controls, one without any control method and the other weeded control. The association between the herbicides and the joint application of the three herbicides provided efficiency above 95% of control for volunteer soybean plants. The mixture of pyrithiobac-sodium and trifloxysulfuron-sodium (42.0 + 3.0 g a.i. ha-1), followed by sequential applications of glyphosate (1,512 g a.i. ha-1), regardless of the form of deposition of the herbicide, provided control above 95%, at 45 days after the first application, for the goosegrass (Eleusine indica) and viola-string (Ipomoea sp) plants. Symptoms of injury were observed in cotton plants, with greater intensity until 15 days after application (DAA), when pyrithiobac-sodium, trifloxysulfuron-sodium and glyphosate (36.4 + 2.25 + 1,350 g a.i. ha-1) were associated, reaching 35.5 % of the affected plants. Plant height was initially affected by the triple association between the herbicides pyrithiobac-sodium, trifloxysulfuron-sodium and glyphosate (36.4 + 2.25 + 1,350 g a.i. ha-1), however, at 90 DAA, all treatments provided higher plant height than the control without herbicide intervention, which was 95.3 cm. For boll weight, no difference was observed between the treatments, other than fiber yield, being lower for the treatments in which glyphosate was associated with pyrithiobac-sodium and trifloxysulfuron-sodium, providing 38.8 and 39.1%, respectively. Cotton yield was influenced by treatments where trifloxysulfuron-sodium was applied associated with glyphosate (2.62 + 1,350 g a.i. ha-1) and pythiobac-sodium, trifloxysulfuron-sodium and glyphosate (36.4 + 2.25 + 1,350 g a.i. ha-1), followed by glyphosate application at 43 DAE, but all treatments were superior to the control without herbicide application. Glyphosate applied alone or in association was essential for weed management in cotton production systems with RF technology.