Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean

Abstract

Walsh, K. D., Soltani, N., Brown, L. R. and Sikkema, P. H. 2014. Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean. Can. J. Plant Sci. 94: 1239–1244. Six field trials were conducted over a 3-yr period (2011, 2012 and 2013) in Ontario, Canada, to evaluate various postemergence (POST) glyphosate tank mixes for weed management in glyphosate-resistant (GR) soybean. Herbicide treatments included glyphosate applied alone or mixed with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl. Glyphosate tank mixtures with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl caused GR soybean injury of up to 21, 11, 4 and 14% at 7 d after treatment (DAT), which was reduced to 5, 0, 0 and 2% by 28 DAT, respectively. Velvetleaf, green pigweed, common ragweed and common lambsquarters control ranged from 55 to 95, 93 to 100, 70 to 92 and 81 to 98% at 28 DAT respectively. Relative to glyphosate alone, tank mixtures with thifensulfuron-methyl provided equivalent to increased weed control, while acifluorfen, fomesafen and bentazon provided equivalent to reduced weed control. All herbicide tank mixtures resulted in higher yields (3.8–4.0 t ha−1) than the untreated check (2.7 t ha−1), and were generally equivalent to glyphosate alone (4.1 t ha−1). Results from this study indicate that the glyphosate tank mixtures evaluated did not provide a benefit over glyphosate alone.