Sensitivity of imidazolinone-resistant red rice resistente as imidazolinonas, aos herbicidas glyphosate e glufosinate

Dose-response experiments were carried out to evaluate the sensitivity of imidazolinone-resistant red rice to nonselective herbicides currently used in rice-soybean rotation in Rio Grande do Sul. Two red rice biotypes previously identified as resistant and susceptible to the imidazolinone herbicides were treated with imazapic plus imazapic, glyphosate and glufosinate under nine herbicide rates. A non-linear log-logistic analysis was used to estimate the herbicide rate that provided 50% red rice control and dry weight reduction ([GR.sub.50]). Imidazolinone-resistant red rice exhibited greater [GR.sub.50] values than imidazolinone-susceptible biotype for imazapyrplus imazapic. In contrast, both imidazolinone-resistant and susceptible red rice showed similar [GR.sub.50] values for glyphosate and glufosinate. These results indicate that glyphosate and glufosinate effectively control imidazolinone-resistant red rice at similar herbicide rates used to control imidazolinone-susceptible; however, integrated weed management practices must be adopted in rice-soybean rotation to delay resistance evolution of red rice populations to glyphosate and glufosinate. Key words: Clearfield® rice, nonselective herbicides, red rice management, rice-soybean rotation, weed resistance. Curvas de dose-resposta foram conduzidas para avaliar a sensibilidade de arroz-vermelho resistente as imidazolinonas para herbicidas nao-seletivos, comumente utilizados em areas de rotacao soja-arroz irrigado no Rio Grande do Sul. Dois biotipos de arroz-vermelho, previamente identificados como suscetivel e resistente as imidazolinonas, foram aspergidos com imazapyr+imazapic, glyphosate e glufosinate sob nove concentracoes herbicidas. Utilizou-se analise de regressao nao linear do tipo log-logistica para estimar a concentracao herbicida que proporcionou 50% de controle e reducao na massa de materia seca da parte aerea ([GR.sub.50]) de arroz-vermelho. O biotipo de arrozvermelho resistente as imidazolinonas demonstrou maior [GR.sub.50], quando comparado ao biotipo suscetivel para imazapyr+imazapic. Valores similares de [GR.sub.50] foram observados para ambos os biotipos tratados com glyphosate e glufosinate. Esses resultados indicam que os herbicidas glyphosate e glufosinate controlam efetivamente biotipos de arroz-vermelho resistente as imidazolinonas em doses recomendadas para controlar biotipos suscetiveis as imidazolinonas. No entanto, praticas integradas de manejo devem ser utilizadas para retarda