Effects of a 28% N solution containing urea and ammonium nitrate (28% UAN) on field efficacy of the methyl ester of thifensulfuron and combinations of thifensulfuron and the methyl ester of chlorimuron were investigated. Velvetleaf control and soybean injury increased as rates of thifensulfuron increased (0, 2.2, 4.4, and 5.8 g ai/ha) and as rates of chlorimuron increased (0, 4.4, and 8.8 g ai/ha). Treatments that included 28% UAN at 9 L/ha controlled velvetleaf 9% better, averaged across herbicides and rates 21 days after treatment (DAT), but also increased soybean injury. Thifensulfuron applications controlled common lambsquarters well, but control was not affected by additions of 28% UAN. In studies where14C-thifensulfuron was applied without an additive to the second true leaf of growth-chamber-grown velvetleaf, less than 4% of that applied was absorbed 84 h after treatment (HAT), whereas treatments that included nonionic surfactant or 28% UAN absorbed 33 and 45%, respectively. When both nonionic surfactant and 28% UAN were added, plants absorbed 76% 84 HAT. Translocation 84 HAT was also greatest with both additives and the majority moved to tissues above treated leaves. The 28% UAN increased uptake of thiameturon regardless of soil fertility level.

Effects of a 28% N solution containing urea and ammonium nitrate (28% UAN) and a nonionic surfactant on efficacy, uptake, and translocation of chlorimuron ethyl ester in soybean and broadleaf weeds were investigated. Chlorimuron applied postemergence at 8.8 and 13 g ai/ha with either nonionic surfactant at 0.25% (v/v), 28% UAN at 9.4 L/ha, or nonionic surfactant plus 28% UAN controlled weeds better than without additives. Chlorimuron with nonionic surfactant and with 28% UAN controlled weeds similarly but with 28% UAN injured soybeans least. Chlorimuron with nonionic surfactant plus 28% UAN controlled velvetleaf best but injured soybeans most. Less than 2% of applied14C-chlorimuron was absorbed in velvetleaf 84 h after treatment (HAT) when no additive was present, but adding nonionic surfactant, 28% UAN, and nonionic surfactant plus 28% UAN resulted in 21, 9, and 32% uptake, respectively, 84 HAT. Nonionic surfactant plus 28% UAN also increased translocation (primarily acropetal) of the14C. Adding 28% UAN increased14C-chlorimuron uptake in velvetleaf grown at low fertility but had no effect under high fertility.