Abstract
Eleven field trials were conducted over a three-year period (2006-2008) at three locations in southwestern Ontario, Canada to evaluate the effect of various weed management strategies in glyphosate-tolerant corn on weed control, crop injury, corn yield, environmental impact and profit margin. No visible injury resulted from the herbicide treatments evaluated. Overall, the effect of all factors assessed were location specific. By 56 days after treatment, depending on location, glyphosate applied at the 7 - 8 leaf stage (LPOST), preemergence (PRE) herbicides followed by (fb) glyphosate LPOST and sequential glyphosate applications (EPOST (3 - 4 leaf stage) followed by LPOST) provided more consistent control of annual broadleaf weeds and annual grasses compared to glyphosate applied alone EPOST. Weed control at 56 days after treatment was lower when glyphosate was applied alone LPOST compared to sequential applications of glyphosate or PRE herbicides fb glyphosate. There were no differences in corn yield among the sequential programs evaluated; however, a yield benefit was found when a sequential program was used compared to glyphosate applied alone LPOST. Among the sequential programs the lowest environmental impact was isoxaflutole/atrazine fb glyphosate. The lowest profit margins were associated with atrazine, S-metolachlor/atrazine/benoxacor, dicamba/atrazine and glyphosate LPOST treatments compared to all other treatments. Overall, profit margins tended to be somewhat higher for treatments that included glyphosate applications. Based on these results, the most efficacious and profitable weed management program in corn was a sequential application of glyphosate; however, isoxaflutole/atrazine fb glyphosate was the treatment with the lowest environmental risk while also adding glyphosate stewardship benefits.
Highlights
The demand on growers to economically produce environmentally sustainable food while maintaining herbicide stewardship is increasing
Eleven field trials were conducted over a three-year period (2006-2008) at three locations in southwestern Ontario, Canada to evaluate the effect of various weed management strategies in glyphosate-resistant corn on weed control, crop injury, corn yield, environmental impact and profit margin
EPOST redroot pigweed control was reduced by 7% compared to LPOST glyphosate, a PRE herbicide fb glyphosate or a sequential glyphosate application
Summary
The demand on growers to economically produce environmentally sustainable food while maintaining herbicide stewardship is increasing. To achieve this goal, data on weed control, crop yield, economics and environmental impacts of herbicides are needed to help identify the most advantageous herbicide program. Growers of glyphosate-resistant corn have several weed management options, including pre-emergence (PRE), post-emergence (POST), tankmixes and sequential applications. Since the introduction of glyphosate resistant corn, one- or two-pass glyphosate-only applications are options that can simplify weed manage-. Sole reliance on glyphosate increases weed selection pressure, potentially selecting for glyphosate-resistant weeds [2,8,9,10]. Tank-mixes or sequential applications that utilize more than one herbicide modes of action can reduce selection pressure [2]
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