XtendFlex® soybean is a new trait platform which confers resistance to three herbicide sites of action that include the active ingredients dicamba, glyphosate, and glufosinate. The ability to use these three herbicides in one system has generated new management questions. Field and greenhouse experiments were conducted in 2019 and 2020 to: 1) investigate weed control systems in conventional and no-tillage XtendFlex® soybean, and 2) identify any antagonistic or synergistic responses from herbicide-tank mixtures used in this system. Control of glyphosate-resistant (GR) waterhemp was optimized with PRE flumioxazin followed by (fb) POST glufosinate or dicamba alone or in combination with each other or glyphosate. Two-pass POST systems also controlled GR waterhemp as long as dicamba and/or glufosinate was used in each application. GR horseweed control was exceptional with all herbicide programs evaluated, except glyphosate alone EPOS or POST. Annual grass control was reduced with EPOS and POST glufosinate + dicamba tank-mixtures. In contrast, this combination was often additive or synergistic for both broadleaf and grass weed control in the greenhouse. Several glyphosate + glufosinate combinations were antagonistic, especially with broadleaf weeds. Dicamba + glyphosate was often antagonistic in the greenhouse but was additive or synergistic for GR waterhemp and GR horseweed control in the field. Antagonisms were often observed when all three herbicides were applied together; however, not all antagonisms resulted in poor control. This research provides growers insight into management strategies for various agronomically important weeds in XtendFlex® soybean.
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