Abstract
Four field trials were conducted on a farm infested with glyphosate-resistant (GR) common ragweed during 2016 and 2017 to evaluate various postemergence (POST) herbicides for the control of GR common ragweed in GR corn. Dicamba at 600 g·a.i.·ha-1, dicamba/diflufenzopyr at 200 g·a.i.·ha-1, dicamba/atrazine at 1500 g·a.i.·ha-1, topramezone + atrazine at 12.5 + 500 g·a.i.·ha-1, bromoxynil + atrazine at 280 + 1500 g·a.i.·ha-1, glufosinate at 500 g·a.i.·ha-1 and 2,4-D ester at 560 g·a.i.·ha-1 provided 58% to 85% control at 4 WAA and 49% to 88% control at 8 WAA. Other herbicides evaluated controlled GR common ragweed 9% to 41%. Common ragweed density was reduced 97%, 95%, 95% and 87% and shoot dry weight was reduced 93%, 95%, 94% and 90% with bromoxynil + atrazine, dicamba, glufosinate and topramezone + atrazine applied POST in GR corn, respectively. Results show that dicamba, bromoxynil + atrazine, topramezone + atrazine and glufosinate applied POST are the most efficacious herbicides among the herbicides evaluated for the control of GR common ragweed in GR corn.
Highlights
The spread of glyphosate-resistant (GR) weeds in North America is threatening the ability of crop producers to sustain the use of glyphosate and glyphosate-resistant crop technology [1]
Dicamba at 600 g∙a.i.∙ha−1, dicamba/diflufenzopyr at 200 g∙a.i.∙ha−1, dicamba/atrazine at 1500 g∙a.i.∙ha−1, topramezone + atrazine at 12.5 + 500 g∙a.i.∙ha−1, bromoxynil + atrazine at 280 + 1500 g∙a.i.∙ha−1, glufosinate at 500 g∙a.i.∙ha−1 and 2,4-D ester at 560 g∙a.i.∙ha−1 were the best treatments among the herbicides evaluated controlling GR common ragweed 58% to 85% at 4 weeks after treatment application (WAA) and 49% to 88% at 8 WAA
In studies conducted in Nebraska under greenhouse conditions, Ganie and Jhala [11] reported excellent (87% - 99%) control of GR common ragweed with 2,4-D, bromoxynil, dicamba/diflufenzopyr, glufosinate, halosulfuron plus dicamba, mesotrione + atrazine and tembotrione applied POST at 3 WAA
Summary
The spread of glyphosate-resistant (GR) weeds in North America is threatening the ability of crop producers to sustain the use of glyphosate and glyphosate-resistant crop technology [1]. In Canada, there are currently six known GR weed species and four of them have been documented in Ontario [1]. Common ragweed is a broadleaf weed from the Asteraceae family with a prolonged emergence pattern which has the potential to produce as much as one billion pollen grains per plant [3]. Common ragweed is a hard-to-control troublesome weed in Ontario. In Ontario, corn yield losses of 38% have been reported with >32 plants m2 of common ragweed [6]. Weaver [6] found as much as 70% yield loss and Van Wely et al [7] found as much as 73% yield loss when common ragweed was not controlled in soybean under Ontario environmental conditions
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