LAUSR

ABSTRACT - Weeds are among the main constraints to high grain yield on hexaploidoat ( Avena sativa ), but there are few herbicides registered for weed control on thiscereal crop. The objectives of this study were to evaluate the impact of theiodosulfuron-methyl on grain yield of elite oat cultivars and investigate the mechanismof oat tolerance to this herbicide. A field experiment conducted in 2012 demonstratedthere was no difference on grain yield between cultivars URS Guara and URS Guria,when iodosulfuron-methyl was used up to 4.5 g ha -1 . Likewise, experiments from2013 have demonstrated that iodosulfuron-methyl, at 5 g ha -1 , did not affect the oatgrain yield of the genotype UFRGS 14, but affected it on the cultivars URS Guara andURS Guria. In 2014, the oat grain yield of five cultivars, including URS Guara, URSGuria and UFRGS 14 was reduced by iodosulfuron-methyl even at only 2.5 g ha -1 .The activity of the ALS enzyme, extracted from oat plants, was sensitive toiodosulfuron-methyl. The increment of the iodosulfuron-methyl effect on oat plantstreated with herbicide-detoxification inhibitors (malathion + chlorpyrifos), or thereduction of the herbicide efficacy in plants sprayed with the stimulator ofdetoxification (mefenpyr-diethyl), suggest that iodosulfuron-methyl degradation isthe mechanism involved on its selectivity to oat plants.