Synergistic enhancement of glyphosate uptake into grasses by adjuvant combinations

Abstract

The influence of various adjuvant combinations on the uptake of glyphosate was examined using a model grass species, wheat. Compared with each of 6 surfactants used alone, a greater uptake enhancement was observed when an aliphatic amine surfactant of higher ethylene oxide (EO) content was mixed with either a linear alcohol or an octylphenol non-ionic surfactant of lower EO content, at equivalent concentration. Surfactant ratio in a mixture was also important in the case of one combination. Three of the positive surfactant combinations were also tested on barnyard grass and their synergistic effect on glyphosate uptake was confirmed. The performance of one of the best surfactant combinations was further compared with a commercial glyphosate formulation by measuring the uptake rate of glyphosate into both wheat and ryegrass plants over a 24-h period. The surfactant mixture provided much faster uptake into both species and also significantly higher overall uptake into ryegrass. Whereas ammonium sulfate could also improve glyphosate uptake into wheat when used at high concentrations and in combination with certain non-ionic surfactants, the enhancing effect of a humectant, glycerol, on uptake was of much lower magnitude and observed only in the presence of super-spreading surfactants. The practical value of using surfactant mixtures is discussed.