Effects of urea ammonium nitrate on bispyribac and penoxsulam efficacy

Experiments were conducted at the Lonoke Extension and Applied Research Center greenhouse at Lonoke, AR, and in fields at the University of Arkansas at Pine Bluff farm near Lonoke, AR, and the Rice Research and Extension Center near Stuttgart, 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) Kinetic® at 0.125% v/v, (3) DyneAmic® at 0.37 L/ha, (4) Dyne-A-Pak ® at 2% v/v, (5) UAN at 2% v/v, (6) Kinetic at 0.125% plus UAN at 2% v/v, or (7) DyneAmic 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 another adjuvant increased herbicide efficacy on barnyardgrass in the greenhouse, with 95 to 99% biomass reduction of 3- to 4-leaf barnyardgrass and 88 to 92% biomass reduction of 1- to 3-tiller barnyardgrass. Barnyardgrass control was also increased by UAN in the field experiment. UAN did not generally increase efficacy on hemp sesbania, as control was 90% or higher with treatments containing the herbicide and a recommended adjuvant. However, when the 0.5X rate of penoxsulam at 24.4 g ai/ha (one-half the labeled rate) was used with COC, hemp sesbania control ranged from 76 to 91%, and increased to at least 97% when UAN was added. Adding UAN did not increase efficacy on broadleaf signalgrass. Broadleaf signalgrass control was highly variable and no treatment provided more than 65% biomass reduction.