Field evaluation of spray quality and environmental risks of unmanned aerial spray systems in mango orchards

Abstract

Unmanned Aerial Spraying Systems (UASS) have garnered substantial market attention as efficient tools for applying Plant Protection Products (PPPs). However, their application has primarily focused on low-growing crops such as rice and wheat. This study emphasizes the need for additional UASS field trial data, specifically addressing spray quality and environmental risks associated with 3D fruit trees. The research aims to quantitatively assess the impact of canopy structure characteristics of mango trees and droplet size on spray quality. Simultaneously, it explores the exposure risks of UASS spraying in orchards to applicators, bystanders, and machine residue, comparing these risks with traditional ground machinery. Research findings reveal substantial differences in the distribution of UASS among mango tree canopies, with variations linked to the size of the canopy. Contrary to expectations, as tree volume increases, droplet deposition does not exhibit exponential growth. More droplets are deposited in the upper part of the canopy rather than the bottom. Altering droplet size significantly influences the deposition and distribution of droplets within the mango tree canopy. Notably, the coverage effect of fine droplets at the bottom of the canopy is 2.5 times that of coarse droplets. The ground loss from ground spray guns was lower than that of UASS, but the exposure risk was higher. Specific body parts with elevated operator exposure risks are identified as the legs and chest. UASS operators are advised to remain vigilant regarding the risk of pesticide adhesion on the equipment rack.