Surfactants Differ in Their Effect on Droplet Retention, Droplet Spread, and Herbicide Efficacy

Abstract

Spray solution must be retained by the leaf before foliar absorption of an herbicide can occur. Once retained, spray droplets can spread on the leaf surface. Experiments were conducted in the greenhouse to determine the effect of twelve surfactants on spray droplet retention, droplet spread, and efficacy of glyphosate [N-(phosphonomethyl) glycine] and imazethapyr {2-[4,5-dihydro-4-(1-methylethyl-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid}. Green foxtail (Setaria viridis) and barley (Hordeum vulgare) were the bioassay species. Spray droplet retention, droplet spread, and herbicide efficacy varied with surfactant. Surfactant enhancement of spray retention did not relate with droplet spread for either herbicide or plant species, nor did spray retention relate with glyphosate or imazethapyr efficacy for green foxtail and barley. Further, efficacy of glyphosate and imazethapyr on green foxtail and imazethapyr on barley did not relate with droplet spread. Glyphosate efficacy on barley generally increased as droplet spread decreased. However, the lack of droplet spread did not always result in a high level of surfactant-enhanced glyphosate efficacy.