Low level resistance of goosegrass (Eleusine indica) to glyphosate in Rio Grande do Sul-Brazil

In the last growing seasons, goosegrass (Eleusine spp.) control failures have been observed following application of glyphosate on Roundup Ready® soybean in Rio Grande do Sul (RS) - Brazil, suggesting this species' resistance to the herbicide. Thus, the objectives of this study were to identify the occurrence of goosegrass resistance to the herbicide glyphosate in RS; and to determine the predominant species of the genus Eleusine, as well as the LD50 and GR50 of the suspected resistant biotypes. Two experiments were conducted under greenhouse conditions: one to identify the biotypes resistant to glyphosate, and the other, a dose-response curve experiment, as well as a study of the botanical characteristics of the species. In the first experiment, 39 biotypes were tested, mainly Eleusine indica, collected with suspected resistance to glyphosate. The glyphosate dose was 2,160 g e.a. ha-1, and the control was evaluated at 28 days after treatment. All biotypes were effectively controlled,with the biotypes from the municipality of Boa Vista do Incra showing greater tolerance. Two biotypes suspected of resistance (12.1 and 12.3) and a susceptible biotype in a dose-response experiment were tested at the following doses: 0, 135, 270, 540, 1,080, 1,620, and 2,160 g e.a. ha-1. The results of this experiment showed that biotype 12.1 does not present resistance to glyphosate and biotype 12.3 has a low level resistance since it is effectively controlled by the herbicide at the maximum dose. Nas últimas estações de cultivo têm-se observado falhas de controle de capim-pé-de-galinha (Eleusine spp.), em resposta à aplicação de glyphosate, em lavouras de soja Roundup Ready® no Rio Grande do Sul (RS), sugerindo a resistência da espécie. Diante disso, os objetivos deste trabalho foram identificar a ocorrência da resistência de capim-pé-de-galinha ao herbicida glyphosate no RS, determinar a (s) espécie (s) do gênero Eleusine e determinar a DL50 e GR50 dos biótipos com suspeita de resistência ao glyphosate. Foram realizados dois experimentos em casa de vegetação, sendo um de identificação de biótipos resistentes ao glyphosate e outro de curva de dose-resposta ao herbicida, além de estudo de caracterização botânica da (s) espécie (s). No experimento de identificação da resistência foram avaliados 39 biótipos, com predominância de Eleusine indica, coletados em áreas com suspeita de resistência ao glyphosate. A dose de glyphosate utilizada foi de 2.160 g e.a. ha-1, sendo avaliado