Glyphosate resistant (GR) Canada fleabane (horseweed) has quickly spread across southwestern Ontario and is a difficult weed to control in GR crops. Glyphosate dimethylamine (DMA)/2,4-D choline (Enlist Duo?TM Dow AgroSciences LLC), a new herbicide premix developed by Dow Agro Sciences, provides control of GR and other problematic weeds. The objective of this study was to compare single and sequential applications of glyphosate DMA/2,4-D choline for the control of GR Canada fleabane in GR corn. Three single applications of glyphosate (DMA)/2,4-D choline (1720 g·ae·ha-1) were evaluated: 1) preplant (PP) applied to Canada fleabane up to 10 cm diameter/height, 2) postplant 1 (POST 1) applied when Canada fleabane was up to 20 cm tall and 3) postplant 2 (POST 2) applied up to 30 cm tall Canada fleabane. Four sequential applications were also examined:1) PP followed by (fb) POST 1, 2) PP fb POST 2, 3) POST 1 fb POST 2 and 4) PP fb POST 1 fb POST 2. The single applications provided 69%-86% control of the GR Canada fleabane while the sequential applications increased control to 92%-100%. Three applications did not provide an increase in control over a sequential two-pass application at 8 weeks after the application (WAA). Results from this research indicate that a sequential 2-pass application of glyphosate DMA/2,4-D choline provided acceptable control of GR Canada fleabane in corn.
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