Interaction of organosilicone surfactant concentration and spray application factors in glyphosate efficacy

Abstract

The interactions between the concentration of an organosilicone, Silwet L-77(R) surfactant, and spray application factors were studied. Uptake of spray solutions via stomata and the herbicidal effects of a sub-lethal rate of glyphosate generally increased with increasing Silwet L-77 concentration (0-0.4%), but the interaction between surfactant concentration and carrier volume (50-800 litres/ha) was highly significant. High surfactant concentrations induced maximal infiltration even at low spray volumes, while low concentrations provided negligible uptake via stomata, except when applied at very high spray volumes. For a constant rate of herbicide, glyphosate efficacy could be accurately predicted by total surfactant dose applied. Fine droplets (150 mu m VMD) induced greater infiltration and herbicide efficacy than coarse droplets (300 mu m VMD).