Interaction of Pyroxasulfone and Encapsulated Saflufenacil Applied Preemergence for Control of Waterhemp in Corn

Waterhemp is a problematic weed in corn production that is rapidly evolving multiple herbicide resistance; 5-way resistance to herbicide groups 2, 5, 9, 14 and 27 has been confirmed in multiple counties across southern Ontario. The introduction of a new premix herbicide, pyroxasulfone plus encapsulated saflufenacil, provides growers with an additional option to control this challenging weed. In 2022 three field trails were conducted at three locations in southwestern Ontario to assess corn injury and yield and waterhemp control, density, and biomass, as well as the interaction between pyroxasulfone and saflufenacil applied preemergence in corn. Herbicide treatments consisted of pyroxasulfone (90, 120, and 150 g ai ha-1), encapsulated saflufenacil (56, 75, and 95 g ai ha-1), pyroxasulfone plus encapsulated saflufenacil (146, 195, and 245 g ai ha-1), and an industry standard, S-metolachlor/atrazine/mesotrione/bicyclopyrone (2026 g ai ha-1). The co-application of both active ingredients improved waterhemp control and resulted in biomass reduction compared to saflufenacil applied alone; waterhemp density and corn yield were similar for pyroxasulfone plus encapsulated saflufenacil or each active ingredient applied alone. The interaction between pyroxasulfone and encapsulated saflufenacil was additive for the majority of assessments; however, there were some parameters where there was an antagonistic or synergistic response.