Control of Glyphosate-Resistant Horseweed in Winter Wheat with Pyrasulfotole Premixed with Bromoxynil

Five experiments were conducted over a 2-yr period (2013 and 2014) to evaluate POST herbicides in winter wheat fields with a history of glyphosate-resistant (GR) horseweed. Control 4 wk after treatment (WAT) with pyrasulfotole + bromoxynil was 95%. Control 8 WAT with 2,4-D, dicamba + MCPA + mecoprop, clopyralid, and pyrasulfotole + bromoxynil ranged from 89 to 97%; these herbicides also reduced GR horseweed density and biomass by 97 to 99%. Single mode of action herbicides like 2,4-D controlled GR horseweed; however, multiple modes of action should be used to prevent populations from becoming incrementally more resistant under repeated selection pressure.