The Addition of Dicamba to POST Applications of Quizalofop-p-ethyl or Clethodim Antagonizes Volunteer Glyphosate-Resistant Corn Control in Dicamba-Resistant Soybean

Two studies consisting of six field experiments each were conducted at three locations in southwestern Ontario, Canada, in 2014 and 2015 to evaluate the possible antagonism when dicamba was added to quizalofop-p-ethyl or clethodim for the control of volunteer glyphosate-resistant (GR) corn. At 4 wk after application (WAA), quizalofop-p-ethyl at 24, 30, or 36 g ai ha(-1) provided 88, 94, and 95% control of volunteer GR corn, respectively. The addition of dicamba at 300 or 600 g ae ha(-1) to quizalofop-p-ethyl (24 g ha(-1)) reduced the activity of quizalofop-p-ethyl on volunteer GR corn by 12 and 20%. At 4 WAA, clethodim at 30, 37.5, and 45 g ai ha(-1) provided 85, 91, and 95% control of volunteer GR corn, respectively. The addition of dicamba at 300 or 600 g ha(-1) to clethodim (30 g ha(-1)) resulted in antagonism, causing a reduction in volunteer GR corn by 12 and 11%, respectively. In general, there was greater antagonism when the high rate of dicamba was tank-mixed with the lower rate of the graminicide. There was no antagonistic effect on soybean yield by tankmixing dicamba with either graminicide at all rates evaluated. Based on these results, volunteer GR corn can be controlled effectively by increasing the rate of the graminicide when tankmixed with dicamba.