ABSTRACT
Weeds are among the main constraints to high grain yield on hexaploid oat (Avena sativa), but there are few herbicides registered for weed control on this cereal crop. The objectives of this study were to evaluate the impact of the iodosulfuron-methyl on grain yield of elite oat cultivars and investigate the mechanism of oat tolerance to this herbicide. A field experiment conducted in 2012 demonstrated there was no difference on grain yield between cultivars URS Guará and URS Guria, when iodosulfuron-methyl was used up to 4.5 g ha-1. Likewise, experiments from 2013 have demonstrated that iodosulfuron-methyl, at 5 g ha-1, did not affect the oat grain yield of the genotype UFRGS 14, but affected it on the cultivars URS Guará and URS Guria. In 2014, the oat grain yield of five cultivars, including URS Guará, URS Guria 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 to iodosulfuron-methyl. The increment of the iodosulfuron-methyl effect on oat plants treated with herbicide-detoxification inhibitors (malathion + chlorpyrifos), or the reduction of the herbicide efficacy in plants sprayed with the stimulator of detoxification (mefenpyr-diethyl), suggest that iodosulfuron-methyl degradation is the mechanism involved on its selectivity to oat plants.
Keywords:
Avena sativa; detoxification; tolerance; acetolactate synthase inhibitor
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The least significant differences for comparing grain yield means between oat cultivars, within herbicide doses, is 550.3 kg ha-1 in B and 347.8 kg ha-1 in C and D. Equations on 
** indicates p = 0.013.
Data was evaluated 28 days after herbicide spray. The least significant differences (LSD) to compare plant height, relative to control, with and without detoxification inhibitor, at the same herbicide rate, is 15.1%; and to compare plant height, relative to control, with and without herbicide antidote, at the same herbicide rate, is 24%. Equations on