Abstract

New weed management strategies are needed to effectively control multiple-herbicide-resistant (MHR) Canada fleabane in corn. Five experiments were established in growers’ corn fields with confirmed MHR Canada fleabane to determine the efficacy of various herbicides applied preplant (PP). In 2021 environments, glyphosate + isoxaflutole + atrazine, glyphosate + isoxaflutole/diflufenican + atrazine, glyphosate + S-metolachlor/atrazine/mesotrione/bicyclopyrone, glyphosate + mesotrione + atrazine, glyphosate/dicamba + isoxaflutole/diflufenican, glyphosate/dicamba + isoxaflutole/diflufenican + atrazine, and glyphosate + saflufenacil/dimethenamid-p provided excellent control (90-100%) of MHR Canada fleabane but glyphosate + S-metolachlor/mesotrione/bicyclopyrone and glyphosate + S-metolachlor/atrazine/mesotrione controlled MHR Canada fleabane 77-84% and 87-96%, respectively at 4, 8, and 12 weeks after application (WAA). Herbicide tankmixes evaluated reduced MHR Canada fleabane density and biomass 91-100%. In 2022 environments, all glyphosate tankmixes evaluated provided 97-100% control, 99-100% density reduction, and 100% biomass reduction of MHR Canada fleabane in corn. In 2021 and 2022 environments MHR Canada fleabane interference reduced corn yield 41 and 32%, respectively; reduced MHR Canada fleabane interference with all herbicide treatments resulted in corn yield similar with the weed-free control. Results of this study indicate that glyphosate + isoxaflutole + atrazine, glyphosate + isoxaflutole/diflufenican + atrazine, glyphosate + S-metolachlor/atrazine/mesotrione/bicyclopyrone, glyphosate + mesotrione + atrazine, glyphosate/dicamba + isoxaflutole/diflufenican, glyphosate/dicamba + isoxaflutole/diflufenican + atrazine, and glyphosate + saflufenacil/dimethenamid-p provide excellent and consistent control of MHR Canada fleabane. However, glyphosate + S-metolachlor/atrazine/mesotrione and glyphosate + S-metolachlor/mesotrione/bicyclopyrone do not provide consistent control of MHR Canada fleabane in corn.

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