Glyphosate-resistant (GR) volunteer corn is one of the most common weed problems found in GR sugarbeet grown in Michigan. Field trials were conducted in 2012 and 2013 at two locations in Michigan. The objectives were to: 1) quantify the impact of GR volunteer corn on GR sugarbeet yield and quality in wide and narrow rows, and 2) identify the optimal time and herbicide for control of GR volunteer corn. A greenhouse trial was also conducted to determine if early-season competition for nitrogen may be contributing to the sugarbeet yield losses associated with volunteer corn. Volunteer corn biomass was 64%, 19%, and 31% lower in narrow rows than in wide rows when combined over volunteer corn densities at Richville 2012, East Lansing 2013, and Richville 2013, respectively. When data were combined over row width, sugarbeet yield was reduced by an average of 19% and 22.5% when GR volunteer corn competed season-long at a density of 1.72 plants m-2 and 3.44 plants m-2, respectively. Volunteer corn emerging simultaneously with sugarbeet required the earliest control to avoid yield loss. When volunteer corn was not controlled prior to the V4 growth stage, sugarbeet yield was reduced by 10%. Greenhouse research indicated that early-season competition for nitrogen is not likely the primary factor contributing to the suppression of sugarbeet growth and yield by volunteer corn. Clethodim and quizalofop were equally effective at controlling volunteer corn in sugarbeet. Implementing timely volunteer corn control strategies and planting sugarbeet in narrow rows can help alleviate the impact that volunteer corn has on sugarbeet yield and quality.
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