Eighteen volatile monoterpenes, which are among the major constituents of essential oils from plants, were screened for phytotoxicity to several crop and weed species. Several monoterpenes containing an oxygen function severely inhibited germination of four different annual weeds while concurrently displaying little effect on soybean germination. Soybeans varied in their sensitivity to various monoterpenes (measured by seedling growth), with α-terpineol and geraniol selectivity inhibiting weed seed germination while having little or no effect on soybeans. All of the monoterpenes tested exhibited relatively high germination and growth inhibition to corn and wheat.

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 where 14C-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.