Abstract
Glyphosate-resistant (GR) giant ragweed has recently been identified in southwestern Ontario and has the potential to be a significant problem for regional corn producers. Eight field trials [four with preplant (PP) and four with postemergence (POST) herbicides] were conducted from 2013 to 2014 on various Ontario farms infested with GR giant ragweed to determine the efficacy of PP and POST tank-mixes in corn. Glyphosate tank-mixed with atrazine, dicamba, dicamba/atrazine, mesotrione plus atrazine, flumetsulam, isoxaflutole plus atrazine, saflufenacil/dimethenamid-P, S-metolachlor/atrazine and rimsulfuron applied PP provided up to 54%, 95%, 93%, 95%, 40%, 89%, 91%, 50% and 93% control of GR giant ragweed and reduced dry weight 69%, 100%, 99%, 100%, 30%, 92%, 98%, 66% and 99%, respectively. POST application of glyphosate alone and tank-mixed with 2,4-D ester, atrazine, dicamba, dicamba/diflufenzopyr, dicamba/atrazine, bromoxynil plus atrazine, prosulfuron plus dicamba, mesotrione plus atrazine, topramezone plus atrazine, tembotrione/thiencarbazone-methyl and glufosinate provided up to 31%, 84%, 39%, 94%, 89%, 86%, 83%, 78%, 72%, 43%, 63% and 58% GR giant ragweed and reduced dry weight 55%, 99%, 72%, 99%, 99%, 98%, 96%, 96%, 93%, 89%, 91% and 95%, respectively. In general, PP control of GR giant ragweed was greater than POST applied herbicides evaluated. Based on these results, glyphosate tank-mixes containing dicamba or mesotrione plus atrazine applied PP, and dicamba applied POST will provide the most consistent control of GR giant ragweed in corn.
Highlights
Giant ragweed (Ambrosia trifida L.) is among the most competitive weeds for corn (Zea mays L.) producers in southwestern Ontario, Canada
The objectives of this study were to determine the efficacy of glyphosate tank-mixed with 2,4-D, atrazine, dicamba, dicamba/atrazine, mesotrione plus atrazine, flumetsulam, isoxaflutole plus atrazine, saflufenacil/dimethenamid-P, S-metolachlor/atrazine and rimsulfuron applied preplant (PP) and glyphosate alone and tank-mixed with 2,4-D ester, atrazine, dicamba, diflufenzopyr, dicamba/atrazine, bromoxynil plus atrazine, prosulfuron plus dicamba, mesotrione plus atrazine, topramezone plus atrazine, tembotrione/thiencarbazone-methyl and glufosinate applied postemergence (POST) for the control of GR giant ragweed in corn, under Ontario field conditions
Excellent control of GR giant ragweed was observed for treatments containing dicamba/atrazine, isoxaflutole plus atrazine, saflufenacil/dimethenamid-P and rimsulfuron which provided 91% to 93%, 84% to 89%, 87% to 91% and 91% to 93% control, respectively
Summary
Giant ragweed (Ambrosia trifida L.) is among the most competitive weeds for corn (Zea mays L.) producers in southwestern Ontario, Canada. Giant ragweed is an aggressive agricultural weed that gains an early competitive advantage by germinating prior to other annual species [2]. A study on competition and fecundity of giant ragweed in corn determined that yield loss was greatest for crops in which the weeds emerged concurrently, relative to crops where giant ragweed emergence was four weeks subsequent [6]. They predicted that a single giant ragweed plant per 10 m−2 could depress corn yields by up to 14% and that a maximum of 90% loss was possible at high weed densities, when weed and crop emergence was simultaneous
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