Field and greenhouse experiments were conducted to determine effects of adding (NH4)2SO4 or urea ammonium nitrate containing 30% N (UAN) and/or substituting BCH 81508 S for crop oil with sethoxydim and sethoxydim plus bentazon applied to corn and large crabgrass. Control was similar with sethoxydim plus crop oil and sethoxydim plus BCH 81508 S. Adding (NH4)2SO4 or UAN moderately improved control with sethoxydim in some experiments. Both (NH4)2SO4 and UAN increased control when added to sethoxydim plus bentazon, with UAN being the more effective ammonium fertilizer. Large crabgrass control with sethoxydim plus bentazon was enhanced more with 1.4 and 2.8 kg/ha (NH4)2SO4 than with 5.6 kg/ha. Substituting BCH 81508 S for crop oil with sethoxydim plus bentazon also increased corn and large crabgrass control. Adding ammonium fertilizers plus substituting BCH 81508 S for crop oil with sethoxydim plus bentazon eliminated antagonism on corn and partially alleviated antagonism on large crabgrass.

The effect of ammonium sulfate on absorption of 14C-sethoxydim applied alone and with bentazon was studied in large crabgrass. Adding ammonium sulfate to 14C-sethoxydim increased 14C absorption 6-fold at 0.5 h after application but did not affect the amount of 14C absorbed 1 or 4 h after application. Applying bentazon with 14C-sethoxydim reduced 14C absorption 26%. When 14C-sethoxydim was applied with bentazon and ammonium sulfate, 14C absorption and translocation were similar to those with 14C-sethoxydim alone.