Spray deposition and coverage on nursery trees from precision applications of a laser-guided variable-rate spray system

A conventional air-assisted sprayer was retrofitted with a laser-guided variable-rate spray control system, allowing operation in either constant-rate mode (CRM) or variable-rate mode (VRM) to improve spray efficiency. Field experiments in a fully foliaged ash tree nursery compared canopy and ground deposition between VRM and CRM. CRM applied a constant 470 L ha⁻¹, while VRM automatically adjusted 212–255 L ha⁻¹ based on tree size, shape, and foliage density. Spray deposits were measured with stainless-steel screens and plastic plates, and coverage was evaluated using water-sensitive papers. VRM resulted 40.8–52.4% of spray volume reduction relative to CRM while achieving comparable canopy deposition (0.92 ± 0.57 vs. 1.13 ± 0.57 µL cm⁻²) and coverage (42 ± 3% vs. 52 ± 6%). Ground deposition was notably lower with VRM (0.17 ± 0.10 µL cm⁻², 4 ± 3% coverage) than CRM (0.38 ± 0.18 µL cm⁻², 9 ± 6% coverage), indicating reduced spray loss. Deposition was more uniform with VRM across canopy and ground locations. Pearson correlation and multiple regression analyses indicated that average wind speeds (0.55–1.04 m s⁻¹) and directions (130–229°) were not able to significantly influence on the variability of average spray deposition inside the canopy and on the ground while the airflow from the sprayer was the dominate factor to carry droplets. Thus, the conventional sprayer retrofitted with the laser-guided VRM system could potentially reduce chemical usage by 50%, reduce ground spray loss by 55%, while maintaining comparable level of spray deposition and coverage inside canopies. This new technology would be greatly beneficial to growers to minimize pesticide waste into the production field and the environment. This study represents an applied field validation of a laser-guided variable-rate intelligent sprayer under commercial nursery conditions. It demonstrates pesticide savings, deposition uniformity, and environmental benefits, providing practical evidence for the real-world adoption of a commercialized smart spraying system (SmartApply™ integrated into John Deere sprayers) and advancing sustainable precision agriculture.