Controle químico de Eleusine indica (L.) Gaertn. em soja Roundup Ready® e resposta de biótipo ao herbicida glifosato

Abstract

In general, in Rio Grande do Sul, the control of weeds in crops genetically modified soybean and resistant to the herbicide Roundup Ready® (RR® soybeans) in no-tillage is performed with glyphosate. However, weeds escapes to the treatment can occur as is the case of goosegrass which is considered by soybean growers plant is difficult to control by glyphosate. In this context, this study aims to evaluate the best combination of herbicide to control goosegrass, combining herbicides applied pre-seeding and post-emergence RR® soybean in two stages of development of this weed (Chapter I). Further evaluate the response of a biotype of goosegrass coming from the municipality of Tupanciretã (RS) to the glyphosate herbicide (Chapter II). The experiment I (Chapter I) was conducted in 2012/2013 harvest in Argisoil Yellow-Red hapludox typical belonging to unit Tupanciretã mapping. The results of the experiment I showed that the paraquat + diuron (200 g i.a. ha-1) and ammonium glufosinate (400 g i.a. ha-1) herbicides are efficient alternatives to glyphosate aiming to desiccation of goosegrass in operation management in RR® soybean pre-seeding. Regardless of desiccant herbicide, the control of goosegrass is higher when the plants receive the application of glyphosate (712 g e.a. ha-1) in vegetative stage three to four tillers, and clethodim (96 g i.a. ha-1) and imazethapyr (106 g i.a. ha-1) herbicides did not satisfactorily control goosegrass in vegetative stage from three tillers in RR® soybeans. Grain yield is higher with the application of glyphosate compared to the clethodim and imazethapyr, when the target is goosegrass with plants in stage three to six tillers. The experiment II (Chapter II) was conducted in the greenhouse of the Department (UFSM), in plastic pots (5 L) containing three seedlings of goosegrass (two to three tillers) with suspected resistance to glyphosate. The treatments consisted of five concentrations of the product (0, 25, 50, 100, 200 and 400% of the dose registry of glyphosate, which is 712 g e.a. ha-1). The results for the control evaluations and production of dry biomass showed that biotype of goosegrass is susceptible to glyphosate, once at the lowest dose registration (712 g e.a. ha-1) tested, the control was greater than 98%.