Abstract
Seven field trials were completed over a three-year period (2016 to 2018) in southwestern Ontario, Canada, to assess weed control in conventional-till dicamba-resistant (DR) soybean with glyphosate/dicamba (2 : 1 ratio) applied postemergence (POST) at 3 doses (900, 1350, and 1800 g·ae·ha−1) and 3 application timings (up to 5, 15, and 25 cm weeds). There was minimal soybean injury (≤2%) from treatments evaluated. Glyphosate/dicamba applied at application timing of up to 5, 15, and 25 cm weeds, controlled Amaranthus spp. (pigweed spp.) 87–96, 94–99, and 99%; Ambrosia artemisiifolia (common ragweed) 93–99, 97–99, and 99–100%; Chenopodium album (lambsquarters) 89–99, 95–100, and 99–100%; Echinochloa crus-galli (barnyardgrass) 81–84, 94–96, and 96–97%; Setaria faberi (giant foxtail) 37–90, 77–98, and 99–100%; and Setaria viridis (green foxtail) 94–96, 99, and 99–100%, respectively. Additionally, glyphosate/dicamba applied POST at 900, 1350, and 1800 g·ae·ha−1 controlled Amaranthus spp. 90–97, 95–98, and 97–99%; A. artemisiifolia 95–98, 97–99, and 99–100%; C. album 92–99, 95–100, and 98–100%; E. crus-galli 84–88, 93-94, and 95-96%; S. faberi 74–95, 75–97, and 79–98%; and S. viridis 98, 98–99, and 98–100%, respectively. Weed interference reduced DR soybean yield as much as 51% compared to the highest yielding treatments. Results indicate that glyphosate/dicamba applied POST at the label doses can provide an adequate control of troublesome weeds in DR soybean. Weed control was generally most consistent when glyphosate/dicamba was applied at the highest registered dose in Ontario (1800 g·ae·ha−1) and when weeds were up to 25 cm tall.
Highlights
Multiple-herbicide-resistant weeds, especially glyphosateresistant (GR) weed biotypes, have increased rapidly in respect to number of weed species and geographic areas affected over the past 12 years in Ontario
Glyphosate/dicamba applied at application timing of up to 5, 15, and 25 cm weeds, controlled Amaranthus spp. 87–96, 94–99, and 99%; Ambrosia artemisiifolia 93–99, 97–99, and 99–100%; Chenopodium album 89–99, 95–100, and 99–100%; Echinochloa crus-galli 81–84, 94–96, and 96–97%; Setaria faberi 37–90, 77–98, and 99–100%; and Setaria viridis 94–96, 99, and 99–100%, respectively
Injury was slightly greater when glyphosate/dicamba was applied at late timing compared to the earlier timings
Summary
Multiple-herbicide-resistant weeds, especially glyphosateresistant (GR) weed biotypes, have increased rapidly in respect to number of weed species and geographic areas affected over the past 12 years in Ontario. Is research was established to assess control of common annual grass and broadleaved weeds in conventional-till DR soybean with glyphosate/dicamba (2 : 1 ratio premix) applied POST at three doses (900, 1350, and 1800 g·ae·ha− 1) and three application timings (up to 5, 15, and 25 cm weeds) in Ontario. Glyphosate/dicamba applied POST at 900, 1350, and 1800 g·ae·ha− 1 controlled A. artemisiifolia 98, 99, and 100% at 4 WAA; 96, 98, and 99% at 8 WAA; and 95, 97, and 99% at 10 WAC, respectively (Table 3).
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