Canada fleabane (Conyza canadensis) control with preplant applied residual herbicides followed by 2,4-D choline/glyphosate DMA applied postemergence in corn

Abstract

Glyphosate resistant (GR) Canada fleabane (Conyza canadensis) is an extremely problematic weed in no-tillage farming operations. A total of five field trials were conducted over a 2-yr (2012 and 2013) period in Ontario to determine the level of GR Canada fleabane control with a two-pass weed control program of a pre plant (PP) residual herbicide followed by 2,4-D choline/glyphosate dimethylamine (DMA) applied POST. Among residual herbicide treatments evaluated, s-metolachlor (1600 g a.i. ha-1) + flumetsulam (50 g a.i. ha-1) + clopyralid (135 g a.e. ha-1) provided the most consistent (95-99%) control across all sites 8 wk after application (WAA). S-metolachlor/atrazine (1800 g a.i. ha-1) did not provide effective GR Canada fleabane control (21-86%) 8 WAA. The preplant residual herbicides followed by 2,4-D choline/glyphosate DMA (1720 g a.e. ha-1) POST provided 97-100% control. Glyphosate (900 g a.e. ha-1) applied PP followed by 2,4-D choline/glyphosate DMA POST provided 80-93% control 8 WAA. The application of 2,4-D choline/glyphosate DMA POST following any PP residual herbicide resulted in 97% or greater control of GR Canada fleabane. Results from this research demonstrate that residual herbicides applied PP followed by 2,4-D choline/glyphosate DMA POST provides excellent control of GR Canada fleabane, and also incorporates different modes of action thereby limiting the selection of resistant weeds.