Weed control, environmental impact and profitability with glyphosate tank mixes in glyphosate-tolerant corn

Eight field trials were conducted over a 3-yr period at Exeter (one site in 2005 and 2006) and Ridgetown (three sites in 2005, two sites in 2006 and one site in 2007), Ontario, to evaluate different postemergence glyphosate tank mixes for weed management in glyphosate-tolerant corn. Treatments included a weedy check, a single application of glyphosate, a sequential application of glyphosate and tank mixes of glyphosate plus either atrazine, dicamba/atrazine, mesotrione, s-metolachlor plus atrazine, s-metolachlor/atrazine, dicamba/diflufenzopyr, and dimethenamid plus atrazine. A single application of glyphosate, the sequential application of glyphosate and tank mixes of glyphosate plus either atrazine, dicamba/atrazine, mesotrione, s-metolachlor plus atrazine, s-metolachlor/atrazine, dicamba/diflufenzopyr, and dimethenamid plus atrazine provided 92-100% control of redroot pigweed, 87-100% control of common ragweed, 74-100% control of common lambsquarters, and 43-100% control of green foxtail. All herbicide treatments had a higher yield than the weedy check. There were no differences in corn yield among the herbicide treatments evaluated. The glyphosate alone or in tank mix combination with mesotrione or dicamba/diflufenzopyr programs had the lowest environmental impact. Glyphosate plus atrazine and dicamba/diflufenzopyr were the most profitable weed management programs in glyphosate-tolerant corn.Key words: Atrazine, dicamba, diflufenzopyr, dimethenamid, glyphosate, mesotrione, pendimethalin, rimsulfuron, s-metolachlor, Zea mays L.