Mixing ammonium sulfate (AMS) can increase dicamba volatility. Therefore, AMS cannot be used with dicamba products in dicamba-resistant soybean. However, most dicamba products applied in corn are labeled to mix with AMS. The objectives of this study were to evaluate broadleaf weed control with dicamba (DiFlexx®) and dicamba/tembotrione (DiFlexx® DUO) applied alone or with AMS or AMS substitute and their effect on broadleaf weed density and biomass. Field experiments were conducted in Illinois, Missouri, and Nebraska in 2018 and 2019. In Illinois and Nebraska, mixing AMS + crop oil concentrate (COC) with dicamba applied at 1,120 g ae ha–¹ increased the control of Palmer amaranth and waterhemp (Amaranthus species) from 78% to 92% and velvetleaf from 73% to 96% compared with dicamba applied alone 14 d after application (DAA); however, Missouri data showed no difference. Mixing AMS + COC with dicamba/tembotrione at 597 and 746 g ai ha–¹ did not improve broadleaf weed control 14 DAA at any site compared with dicamba/tembotrione applied alone. Control of Amaranthus species was increased from 82% with dicamba applied at 840 g ae ha–¹ to 96% when mixed with AMS + COC 28 DAA in Illinois; however, control was similar to dicamba applied at 1,120 g ae ha–¹. Broadleaf weed control did not differ among dicamba or dicamba/tembotrione 28 and 56 DAA in Missouri and Nebraska. Broadleaf weed density decreased from 64 plants m^–2 to 24 plants m^–2 with dicamba at 1,120 g ae ha–¹ with AMS + COC 14 DAA in Nebraska; however, no differences were observed in broadleaf weed density or biomass 56 DAA in any state. The results suggest that dicamba or dicamba/ tembotrione can be applied without AMS or AMS substitute, especially at higher rates, without losing broadleaf weed control efficacy.

Nomenclature: Dicamba; dicamba/tembotrione; Palmer amaranth; Amaranthus palmeri S. Watson (AMAPA); velvetleaf; Abutilon theophrasti Medik. (ABUTH); waterhemp; Amaranthus tuberculatus (Moq.) J.D. Sauer (AMATU); corn; Zea mays L.; soybean; Glycine max (L.) Merr.