There is little information on tolerance of glyphosate-resistant maize to glyphosate plus MCPA amine as influenced by dose and\ntiming underOntario environmental conditions.Atotal of seven field trialswere conducted at various locations inOntario,Canada,\nin 2011ââ?¬â??2013 to evaluate tolerance of field maize to tank mixes of glyphosate (900 g a.e./ha) plusMCPA amine (79, 158, 315, 630, 1260,\n2520, or 5040 g a.e./ha) at either the 4- or 8-leaf stage. The predicted dose ofMCPA amine that caused 5, 10, and 20% injury was 339,\n751, and 1914 g a.e./ha when applied to 4-leaf maize but only 64, 140, and 344 g a.e./ha when applied to 8-leaf maize, respectively.The\npredicted dose of MCPA amine that caused 5, 10, and 20% reduction in shoot dry weight of maize was 488, 844, and 1971 g a.e./ha\nwhen applied to 4-leaf maize and only 14, 136, and 616 g a.e./ha when applied to 8-leaf maize, respectively. The predicted dose of\nMCPA amine that caused 5, 10, and 20% yield reduction was 2557, 4247, and >5040 g a.e./ha when applied to 4-leaf maize and 184,\n441, and 1245 g a.e./ha when applied to 8-leaf maize, respectively. Based on these results, glyphosate plus MCPA amine applied at the\nmanufacturerââ?¬â?¢s recommended dose of 630 g a.e./ha applied to 4-leaf maize has potential to cause injury but the injury is transient\nwith no significant reduction in yield. However, when glyphosate plus MCPA amine is applied to 8-leaf maize it has the potential\nto cause significant injury and yield loss in maize.
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