Experiments were conducted at the Lonoke Extension and Applied Research Center greenhouse at Lonoke, AR, to evaluate the effects of urea ammonium nitrate (UAN) on bispyribac and penoxsulam efficacy on barnyardgrass, hemp sesbania, and broadleaf signalgrass. Herbicide treatments included bispyribac at 17.9 or 35.8 g ai/ha or penoxsulam at 24.4 or 48.9 g ai/ha tank mixed with (1) no adjuvant, (2) a nonionic organosilicone (OSL) adjuvant at 0.125% v/v, (3) a methylated seed oil/organosilicone (MSO/OSL) adjuvant at 0.37 L/ha, (4) a proprietary blend of MSO/OSL/UAN at 2% v/v, (5) UAN at 2% v/v, (6) OSL at 0.125% plus UAN at 2% v/v, or (7) MSO/OSL at 0.37 L/ha plus UAN at 2% v/v. In addition to these adjuvants, penoxsulam was also applied with crop oil concentrate (COC) at 2.34 L/ha and with COC at 2.34 L/ha plus UAN at 2% v/v. The addition of UAN to either herbicide plus an adjuvant increased herbicide efficacy on barnyardgrass in the greenhouse, with 95 to 99% biomass reduction of three- to four-leaf barnyardgrass and 88 to 92% biomass reduction of one- to three-tiller barnyardgrass. UAN did not generally increase efficacy on hemp sesbania, as control was 90% or higher with treatments containing either herbicide and a recommended adjuvant. Adding UAN did not increase efficacy on broadleaf signalgrass. Broadleaf signalgrass control was highly variable and no treatment provided more than 65% biomass reduction.