A greenhouse experiment was conducted to evaluate the herbicidal activity of five aliphatic (ethyl, propyl, butyl, allyl, and 3-methylthiopropyl) and three aromatic (phenyl, benzyl, and 2-phenylethyl) isothiocyanates (ITCs) on Palmer amaranth, pitted morningglory, and yellow nutsedge. All ITCs were applied to soil at 0, 10, 100, 1,000, and 10,000 nmol g⁻¹ of soil and incorporated. All ITCs had a deleterious effect on Palmer amaranth and pitted morningglory emergence. LC₅₀ values for Palmer amaranth emergence inhibition from aliphatic and aromatic ITCs ranged from a low of 32 nmol g⁻¹ of soil for phenyl ITC to a high of 941 nmol g⁻¹ of soil for propyl ITC. Pitted morningglory was slightly more tolerant than Palmer amaranth to each of the ITCs, with LC₅₀ values for emergence ranging from 347 to 2,855 nmol g⁻¹ of soil for 3-methylthiopropyl and butyl ITC, respectively. Yellow nutsedge was the most tolerant of the three species, with LC₅₀ values for ethyl, butyl, benzyl, and 2-phenylethyl being greater than the highest evaluated concentration of 10,000 nmol g⁻¹ of soil. Phenyl and 3-methylthiopropyl at 10,000 nmol g⁻¹ of soil were the most effective ITCs against yellow nutsedge, reducing emergence by 92%. Effectiveness of the ITCs varied across structure and species, but 3-methylthiopropyl and phenyl ITC were generally the most efficacious for the three species evaluated.

Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; yellow nutsedge, Cyperus esculentus L. CYPES.