The development of commercial rice genotypes resistant to herbicides of the imidazolinone chemical group has proved to be an effective method for the selective control of red rice (Oryza sativa) in flooded rice culture. However, the continued use of this technology led to the development of populations of red rice resistant to the herbicides used in their control. The objective of this study was to evaluate the occurrence of resistance in red rice populations by dose response curves through level of resistance (LR). Non-controlled populations of red rice from rice fields cultivated under the Clearfield System in the state of Rio Grande do Sul were evaluated under greenhouse conditions in relation to their sensitivity to the herbicide Only (imazethapyr + imazapic - 75 + 25 g L-1). The dose response result confirms that 56% of the red rice populations are resistant and that they can be grouped according to low (FR=5.2) and high (FR=11.6) levels of resistance to the herbicides imidazolinones.
rice crop (Oryza sativa); cv. IRGA 422 CL; herbicide Only
