Submitted to: American Society for Testing and Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2016
Publication Date: 12/15/2016
Citation: Fritz, B.K., Hoffmann, W.C., Henry, R. 2016. The effect of adjuvants at high spray pressures for aerial applications. American Society for Testing and Materials. doi:10.1520/STP159520150086.

Interpretive Summary: As agricultural aircraft get larger and fly faster, maintaining droplet sizes required by most agrochemical product labels becomes a challenge with currently available spray nozzles and application methods. Scientists with the USDA ARS in College Station, Texas have demonstrated that adapting spraying system to use higher than normal spray pressures results in larger droplet sprays at higher airspeeds that meet chemical product label requirements. While implementation of higher pressure spraying may require modifications to current aircraft pump and circulation systems, the standard plumbing and nozzle technologies are sufficient to operate at the higher pressures tested. Higher pressure spraying offers aerial applicators a ready method for overcoming the effects of higher airspeeds on spray droplet breakup and allow them to make more efficient application while adhering to agrochemical application requirements.

Technical Abstract: 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 dominate 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 which reduces 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 combination 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 allow for more efficient applications while meeting agrochemical product label requirements.