Potential Improvement of an Air-Conveyor Sprayer Performance Using a Spray Controller in Pear Orchard

Abstract

Highlights An orchard sprayer was equipped with a spray controller to monitor and manage the working conditions. Foliar deposits and losses of the optimized and conventional sprayer were tested on two different sized pear trees. No significant differences in leaf deposits were found between canopy positions with the optimized sprayer. Ground losses with the optimized sprayer in the target rows were 45% lower compared to the conventional sprayer. Abstract. Currently, mistblowers are the most common sprayer type used for pesticide application in orchards. However, maximizing canopy deposition with high application efficiency remained a challenge due to the intricate canopy structure. This study compares the performance of two air-conveyor sprayers on pear trees: a conventional sprayer and an optimized sprayer. The optimized sprayer was equipped with a spray controller that displays its operational conditions (forward speed, spraying pressure, etc.) during application through a user interface of the device. In addition, the controller was capable of recommending spray volume for an orchard with the operator’s inputs based on the Tree Row Volume (TRV) method. Two experimental blocks in two pear orchards, with different tree sizes referred to as 'small trees' and 'large trees', were designated to evaluate the foliage deposition and off-target losses of the two sprayers. The conventional sprayer applied a spray volume of 1160 L ha-1 on both orchards following the farmers' conventional procedure. In contrast, the spray volumes of the optimized sprayer were determined by the controller based on the TRV model, resulting in a reduction of 29% and 55% for the large and small pear trees, respectively. The foliar deposition of each block was sampled from five randomly selected trees in a central row, with leaves collected from nine different canopy positions for small trees and twelve positions for large trees. Petri dishes were placed on the ground to assess the ground losses. Poles with nylon threads were mounted at various positions to evaluate airborne drift. The results showed that the mean normalized foliar depositions of the optimized sprayer were 1.57 and 1.81 µg cm-2 / kg-1 tracer ha-1 for large and small trees, respectively, whereas with the conventional sprayer, the depositions were 0.85 and 2.11 µg cm-2 / kg-1 tracer ha-1 for large and small trees, respectively. The optimized sprayer achieved a more uniform deposition distribution throughout the canopy compared to the conventional sprayer, as no significant differences in foliage deposition were detected between positions with the optimized sprayer. The optimized sprayer was capable of providing higher normalized deposits than the conventional sprayer for the large trees with less application volume. In addition, the optimized sprayer reduced spray losses in the air by 10% and 64% compared to the conventional sprayer for small and large trees, respectively, whereas ground losses were diminished by 45% and 50%, respectively. The results of this study suggest that controlling sprayer parameters, along with the spray volume adjustment based on canopy characteristics, may increase foliar deposition and could reduce pesticide use, although its influences on off-target loss reduction were insignificant. Keywords: Air conveyor, Constant-rate application, Digital control, Off-target losses, Pear fruit, Pesticide spraying, Tree row volume.