Control of Glyphosate Resistant Canada Fleabane (Conyza canadensis (L.) Cronquist) with 2,4-D Choline/Glyphosate DMA in Corn (Zea mays L.)

Glyphosate resistant Canada fleabane (GRCF) exists in Ontario due to the repeated use of glyphosate on Roundup Ready crops. GR weeds must now be managed using an integrated approach including herbicides like, 2,4-D choline/glyphosate DMA, a premixed herbicide solution. The objective of this research was to determine the ideal application timing of 2,4-D choline/glyphosate DMA herbicide for the control of GRCF. Single applications of 2,4-D choline/glyphosate DMA (1720 g ae ha-1) provided 71-93% control, while sequential applications provided 98-100% control of GRCF 8 WAA. S-metolachlor (1600 g ai ha-1) + flumetsulam (50 g ai ha-1) + clopyralid (135 g ae ha-1) applied preemergence provided the best consistent control of GRCF (95-99%) of the preplant corn residual herbicides evaluated. 2,4-D choline/glyphosate DMA applied post-emergence provided 97-100% control of GRCF following any preplant corn residual herbicide. The size of the GRCF (10, 20 and 30 cm tall) at the time of the 2,4-D choline/glyphosate DMA application did not affect the efficacy of the herbicide. The 2,4-D choline/glyphosate DMA formulation and a tank mix of 2,4-D amine and glyphosate DMA provide equivalent control of GRCF. Dow AgroSciences LLC