SURFACTANT EFFECTS ON GLYPHOSATE EFFICACY

Field and greenhouse studies were performed to examine the influence o f various surfactants with glyphosate on whole plant efficacy. Relatio nships were examined between glyphosate phytotoxicity and surfactant p roperties, including ionic form, degree of ethoxylation, and hydrophob e composition. Cationic tertiary amine surfactants enhanced glyphosate performance in both field and greenhouse studies. Nonionic allinol an d octoxynol surfactants were not effective in combination with glyphos ate. In field studies, glyphosate efficacy increased with increasing s urfactant ethylene oxide (EO) content. Soybean and velvetleaf responde d similarly to glyphosate-surfactant spray applications, as both demon strated significant linear and quadratic relationships between increas ing surfactant ethoxylation and phytotoxicity, while common lambsquart ers showed a significant linear relationship only, Cationic surfactant s were evaluated in the greenhouse and a significant quadratic regress ion of glyphosate phytotoxicity to common lambsquarters on increasing surfactant ethoxylation indicated an optimum surfactant EO content of about 10 moles, Both tertiary and quaternary ethoxylated fatty amines were effective with glyphosate in decreasing common lambsquarters' fre sh weight, Fatty amine hydrophobe composition did not correlate with g lyphosate phytotoxicity to common lambsquarters. Nomenclature: Glyphos ate, N-(phosphonomethyl)glycine; common lambsquarters, Chenopodium alb um L. #(3) CHEAL; velvetleaf, Abutilon theophrasti Medicus # ABUTH; so ybean, Glycine max (L.) Merr. 'Elgin.'