PRECISION SPRAYING IN ORCHARD CROPS: FROM CANOPY PERCEPTION TO CROP PROTECTION OUTCOMES - A CRITICAL REVIEW AND INTEGRATED FRAMEWORK

Abstract

Precision spraying is increasingly being developed to address the limitations of uniform-rate pesticide application in orchard crops, where substantial spatial variation in canopy structure can lead to excessive application, inadequate deposition and off-target losses. This review critically examines the transition from conventional orchard spraying toward canopy-responsive precision spraying, with emphasis on the complete pathway from canopy sensing to crop-protection outcomes. Technologies including ultrasonic sensors, LiDAR, RGB/RGB-D vision, multispectral sensing and artificial intelligence are evaluated for their ability to characterize canopy size, density and three-dimensional structure. The review further examines how canopy information is converted into spray prescriptions through variable-rate strategies, including flow regulation, pulse-width modulation, solenoid valve control and spatial prescription mapping. Particular attention is given to the interaction between spray-rate adjustment, droplet deposition, coverage, drift and biological efficacy, highlighting that pesticide-volume reduction alone is insufficient to demonstrate successful precision crop protection. Recent developments in intelligent, autonomous and UAV-based spraying are also assessed alongside their environmental, energy and economic implications. A cross-study synthesis identifies persistent gaps in sensor generalization, canopy-to-spray modelling, sensing-to-actuation synchronization, standardized performance assessment and biological validation. Based on these findings, a Canopy-to-Crop-Protection (C2CP) framework is proposed, linking canopy perception, canopy interpretation, spray prescription, real-time execution, deposition assessment and biological feedback. The framework provides a system-level perspective for developing precision spraying technologies that deliver the required crop protection while minimizing unnecessary pesticide use and off-target losses.