Red rice is one of the major troublesome and difficult weeds to control in rice production regions. The introduction of the Clearfield® technology allowed producers to control red rice using rice genotypes tolerant to the imidazolinone herbicides. However, because the consecutive use of this technology red rice biotypes have evolved resistance to imidazolinone herbicides, the rice-soybean rotation has been an alternative used by producers to control this weed. This system allows the use of herbicides with different modes of action to control red rice, such as S-metolachlor. Thus, greenhouse and field experiments were carried out during the 2011 to 2012 and 2012 to 2013 growing seasons to evaluate: 1) sensitivity of imidazolinone-resistant red rice to S-metolachlor; 2) red rice control and soybean tolerance in response to associations of S-metolachlor and glyphosate. In greenhouse, S-metolachlor effectively controlled both susceptible and imidazolinone-resistant red rice in preemergence. In field, preemergence applications of S-metolachlor provided greater red rice control in comparison to S-metolachlor alone in early postemergence. The association of S-metolachlor with glyphosate did not improve red rice control in preemergence application. However, association of S-metolachlor with glyphosate significantly improved red rice control in early postemergence applications. S-metolachlor injury to soybean increased with early postemergence applications. These results indicate that S-metolachlor effectively control imidazolinone-resistant red rice in rice-soybean rotation.
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