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1 June 2016 Biologically effective dose of glyphosate as influenced by weed size in corn
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There is limited information on the effect of weed size at the time of application on glyphosate efficacy in Ontario. Eleven field trials were conducted over a 3 yr period (2010–2012) in Ontario to determine the biologically effective dose of glyphosate applied postemergence (POST) in corn at doses of 112.5–1350 g acid equivalent (a.e.) ha-1 for the control of various grass and broadleaved weed species when the weeds were 10, 20 or 30 cm in height. The GR90 for redroot pigweed, common ragweed, common lamb's-quarters, barnyardgrass, and green foxtail were 353, 630, 621, 763, and <112.5 g a.e. ha-1 when applied at 10 cm weed height, 235, 201, 906, 868, and 296 g a.e. ha-1 when applied at 20 cm weed height, and 792, >1350, >1350, 912, and 675 g a.e. ha-1 when applied at 30 cm weed height, respectively. Corn yields were maximized when glyphosate was applied to weeds that were up to 10 cm in height, but was reduced with later glyphosate application timings. The results of this study reinforce the importance of early POST weed control in corn.

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Nader Soltani, Robert E. Nurse, and Peter H. Sikkema "Biologically effective dose of glyphosate as influenced by weed size in corn," Canadian Journal of Plant Science 96(3), 455-460, (1 June 2016).
Received: 27 August 2015; Accepted: 1 January 2016; Published: 1 June 2016

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