Glyphosate and glufosinate resistant (RR/LL) volunteer corn has become a problem when hybrid RR/LL corn follows hybrid RR/LL corn in the rotation. A total of six field trials were conducted over a three-year period (2008 to 2010) in southwestern Ontario to 1) evaluate the competitiveness of volunteer RR/LL corn in hybrid RR/LL corn, and 2) determine how to control volunteer RR/LL corn in hybrid RR/LL corn. The predicted volunteer RR/LL corn density to reduce hybrid RR/LL corn yield by 5% was 1.7 volunteer RR/LL corn plants m-2. There was no crop injury in hybrid RR/LL corn with herbicides evaluated at 1 and 2 WAA except for rimsulfuron(15 g·ai·ha-1) and foramsulfuron (35 g·ai·ha-1) which caused as much as 5% and 11% injury in hybrid RR/LL corn, respectively. Glyphosate (1800 g·ae·ha-1), glufosinate(500 g·ae·ha-1) and glyphosate + glufosinate (1800 + 500 g·ae·ha-1) provided up to 18%, 10% and 21% control of volunteer RR/LL corn, respectively. The POST application of rimsulfuron (15 g·ai·ha-1), nicosulfuron (25 g·ai·ha-1), nicosulfuron/rimsulfuron (25 g·ai·ha-1), foramsulfuron (35 g·ai·ha-1), and primisulfuron/dicamba (166 g·ai·ha-1) did not provided any control of volunteer RR/LL corn. Glyphosate and glyphosate + glufosinate reduced volunteer corn density 26% and 30%, respectively. The other herbicides evaluated did not reduce volunteer RR/LL corn density compared to the weedy control. None of the herbicides evaluated reduced volunteer RR/LL corn cob numbers compared to the weedy control. Glyphosate + glufosinate applied POST reduced volunteer RR/LL corn yield 35% compared to the weedy control but other herbicides evaluated caused no reduction in volunteer RR/LL corn yield compared to the weedy control. Glyphosate applied POST resulted in hybrid RR/LL corn yield equivalent to the weed free control but all other herbicide treatments resulted hybrid RR/LL corn yield equivalent to the weedy control. This research concludes that volunteer RR/LL corn can be very competitive with RR/LL hybrid corn. None of the herbicides evaluated provided adequate control of volunteer RR/LL corn in hybrid RR/LL corn.
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