-The objectives of this study were to determine the effect of herbicide ethoxysulfuron on the development of commom bean (Phaseolus vulgaris), to evaluate the impact of the herbicide on the crop grain yield and to determine the mechanism of tolerance of common bean to ethoxysulfuron. Field experiments were carried out with several doses of ethoxysulfuron to determine its effect on the grain yield of two varieties of common bean ("IPR Andorinha", "IPR Tangará"). The mechanism of plant tolerance was evaluated through several methods, including the analysis of the ALS enzyme sensitivity to herbicide and the use of P450 inhibitors (the insecticides malathion + chlorpyrifos) and the use of antidote (mefenpyr-diethyl). When the rate of ethoxysulfuron was 83.2 g ha -1 , the grain yield loss reached 25% (IPR Tangará) and 35% (IPR Andorinha). The ALS enzyme activity was severely reduced even at low concentrations ethoxysulfuron (1 μM), indicating that the mechanism of tolerance is not the insensitivity of the herbicide target enzyme. The inhibitors of herbicide detoxification increased the sensitivity of the bean plants to ethoxysulfuron, and the antidote (stimulator of herbicide degradation) mitigated the herbicidal effect. These results strongly support the hypothesis that the mechanism of tolerance of common bean plants to ethoxysulfuron is enhanced herbicide detoxification.Keywords: Phaseolus vulgaris, crop grain yield, ALS enzyme, detoxification.
RESUMO -Os objetivos deste trabalho foram determinar o efeito do herbicida ethoxysulfuron sobre o desenvolvimento do feijoeiro (Phaseolus vulgaris), avaliar o impacto do herbicida sobre o rendimento de grãos e determinar o mecanismo de tolerância do feijoeiro ao ethoxysulfuron. Em campo, foram realizados dois experimentos com doses crescentes de ethoxysulfuron, a fim de determinar o seu efeito sobre o desenvolvimento e o rendimento de grãos de dois cultivares (cvs.) de feijão (IPR Andorinha e IPR Tangará). O mecanismo de tolerância das plantas foi determinado através da análise de sensibilidade da enzima ALS ao herbicida, do uso de inseticidas inibidores da P450 (malathion + chlorpyrifos) e do uso de antídoto (mefenpyr-diethyl). Quando a dose de ethoxysulfuron foi de 83,2 g ha -1 , as perdas de rendimento de grãos atingiram 25% (IPR Tangará) e 35% (IPR Andorinha