Agricultural Research Division of IANR


Date of this Version



Fritz, B. K., Hoffmann, W. C., and Henry, R. S., “The Effect of Adjuvants at High Spray Pressures for Aerial Applications,” Pesticide Formulation and Delivery Systems: 36th Volume, Emerging Trends Building on a Solid Foundation, ASTM STP1595, C. Poffenberger and J. Heuser, Eds., ASTM International, West Conshohocken, PA, 2016, pp. 133–148, STP159520150086


Copyright 2016 by ASTM International. Used by permission.


Controlling droplet size is a critical part of making any successful agrochemical spray application. This is particularly true for higher-speed aerial applications where secondary atomization from air shear becomes the most dominant factor driving spray droplet size. Previous research has shown that higher spray pressures can result in larger droplet-sized sprays by increasing the exit velocity of the spray liquid from the nozzles, which in turn decreases the differential velocity between the spray liquid and surrounding airstream, reducing secondary breakup. This work explores the effects of higher-than-normal spray pressures on two typical aerial application nozzles in the presence of a formulated herbicide spray solution, with and without additional adjuvants. Generally, the spray solution effects followed trends seen in previous studies, with crop oil-containing adjuvants resulting in the largest droplet-sized sprays and the silicones and polymers the smallest. Increasing spray pressure increased droplet size across all combinations of nozzle, airspeed, and spray solution, without exception. The most promising results from this work showed that for typical high-end application airspeeds, increasing spray pressure from the lowest to highest pressures tested generally resulted in spray classifications increasing at least one size coarser. The results from this work demonstrate that larger, faster-flying agricultural aircraft can adopt current methods, with potentially minor equipment adjustments, to generate medium and larger spray qualities and to allow for more efficient applications while meeting agrochemical product label requirements.