Evaporation and spread of droplets with various types and concentrations of adjuvants on waxy and hairy leaves

Abstract

Adjuvants have been used to improve pesticide application efficiency and effectiveness for many years. However, knowledge on quantitative reactions of adjuvant-amended pesticide droplets on foliage is lacking. Evaporation rate and wetted area of 500 m droplets with four different adjuvants on waxy and hairy leaves were measured inside an environment-controlled chamber. The adjuvants included Crop Oil Concentrate (COC), Modified Seed Oil (MSO), Nonionic Surfactant (NIS), and Oil Surfactant Blend (OSB). Droplet evaporation rate and spread on either waxy or hairy leaves varied greatly with the type of adjuvants. On waxy leaves, droplets containing COC had significantly smaller wetted area than those containing MSO, NIS or OSB while the evaporation rate was opposite. On hairy leaves, droplets containing COC remained on top of hairs and did not reach the epidermal surface of leaves. When the relative concentration was 1.50, the wetted area of droplets with NIS was 9.2 times lower than that with MSO and 6.1 times lower than that with OSB. The wetted area increased as the concentration increased. Droplets with MSO or OSB spread extensively on the hairy leaf surface until they dried completely. Results of this study demonstrated that addition of MSO, NIS or OSB into spray mixtures with proper concentrations improved homogeneity of spray coverage on both waxy and hairy leaf surfaces, leading to pesticide reduction strategies.