Response of goosegrass (Eleusine spp.) to the herbicide glyphosate

O capim p??-de-galinha (Eleusine spp.) ?? uma planta anual, presente em cultivos agr??colas do Rio Grande do Sul (RS), onde tem-se observado falhas de controle em resposta a aplica????o de glyphosate, sugerindo a resist??ncia da esp??cie a esse herbicida. Diante disso, os objetivos da pesquisa foram identificar a ocorr??ncia da resist??ncia de capim p??-de-galinha ao glyphosate no RS, determinar a DL50 e GR50, identificar o mecanismo de resist??ncia, avaliar os fatores envolvidos nas falhas de controle observadas, e propor alternativas para o controle qu??mico destes bi??tipos. Para isso, sementes de plantas oriundas de falhas de controle do glyphosate, suspeitas de resist??ncia, foram coletadas em lavouras de oito munic??pios produtores de soja no RS, e utilizadas nos experimentos. Os resultados demonstraram que todas as plantas oriundas das sementes coletadas foram controladas pelo glyphosate quando aplicado na dose de 2160 g e.a. ha-1. O bi??tipo 12.3, oriundo de Boa Vista do Incra, apresenta resist??ncia de n??vel baixo ao glyphosate, com fator de resist??ncia (FR) de 1,17, baseado na DL50, e o mecanismo que confere a resist??ncia n??o ?? decorrente de metabolismo do glyphosate pelo complexo cyt-P450 ou absor????o do herbicida. Os bi??tipos com suspeita de resist??ncia apresentam controle inferior quando o glyphosate ?? aplicado em est??dios de crescimento avan??ados, como um ou dois afilhos, podendo ser a causa das falhas de controle observadas em lavouras. Os herbicidas inibidores da ACCase (clethodim e fluazifop-p-butyl) e o amonium-glufosinate controlam eficientemente estes bi??tipos, nos est??dios de quatro folhas a um afilho, sendo alternativa para o controle qu??mico desta planta daninha.The goosegrass (Eleusine spp.) is an annual plant, found in agricultural crops in Rio Grande do Sul (RS), where has been control failures in response to glyphosate application, suggesting the resistance of the species to this herbicide. The objectives of this research were to identify the occurrence of resistance of goosegrass to glyphosate in RS, determine the LD50 and GR50, identify the mechanism of resistance, evaluate the factors involved in the observed control failures, and propose alternatives to chemical control to these biotypes. Thus, plant seeds of failures herbicide control, suspected of resistance, were collected in eight cyties soybean producers in RS, and used in the experiments. The results showed that all the plants from seeds collected has been controlled by glyphosate when applied at a rate of 2160 g a.e. ha-1. The biotype 12.3, from Boa Vista do Incra, show a low level resistance to glyphosate, with resistance factor (RF) of 1.17, according to LD50, and the mechanism that confers resistance is not due to the metabolism of glyphosate by cyt-P450 complex, or herbicide absorption. The suspected resistant biotypes have lower control when glyphosate is sprayed in advanced stages of growth, as one or two tillers, that may be the cause of control failures observed in crop area. The ACCase inhibiting herbicides (clethodim and fluazifop-p-butyl) and amonium-glufosinate efficiently control these biotypes, at four leaves to a one tiller stage, being an alternative to chemical control of this weed