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

Authors: You, Kyusuk; Zhu, Heping; GULER, H - Ege Forestry Research Institute; MEHTA, S - University Of Florida

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2025
Publication Date: 10/31/2025
Citation: You, K., Zhu, H., Guler, H., Mehta, S. 2025. Spray deposition and coverage on nursery trees from precision applications of a laser-guided variable-rate spray system. Precision Agriculture. 12. Article 101589. https://doi.org/10.1016/j.atech.2025.101589.
DOI: https://doi.org/10.1016/j.atech.2025.101589

Interpretive Summary: Traditional pesticide sprayers apply chemicals at a fixed rate across entire field, regardless of individual plant needs, leading to excessive pesticide use, high costs, and unintended environmental pollution. To address the challenge, a conventional air-assisted sprayer retrofitted with a newly developed laser-guided variable-rate intelligent spray control system was developed. The retrofit allowed the sprayer to automatically adjusting spray outputs based on the presence and canopy volume of each tree. The sprayer was investigated for precision delivery of adequate spray deposition inside 5 m tall trees in a nursery field. Test results demonstrated that the retrofitted sprayer provided comparable spray deposition quality inside tall nursery trees and improved spray coverage uniformity, compared to the same sprayer without using the spray control system. At the same time, the retrofitted sprayer reduced spray volume by 41% to 52%, which can be translated to the same percent reductions in pesticide use and cost savings. In addition, the retrofitted sprayer reduced spray loss to the ground by 55%. Thus, the intelligent spray technology has great potential to enhance spray application efficiency with reduced pesticide use and minimized environmental risk for tree nursery applications.

Technical Abstract: A laser-guided variable-rate spray control system was retrofitted onto a conventional air-assisted sprayer, allowing the operator to switch between constant-rate mode (CRM) and variable-rate mode (VRM). To evaluate the performance of the retrofitted spray system, field experiments were conducted in a nursery field to compare spray deposition and coverage within fully foliaged ash tree canopies and on the ground between VRM and CRM treatments. CRM maintained a constant application rate of 445 L ha-1, while the VRM automatically adjusted rates between 212 and 255 L ha-1 based on tree shape, size, and foliage density. Spray deposits were collected with stainless steel screens and plastic plates, and spray coverage levels were accessed with water-sensitive papers. Test results showed that VRM reduced spray volume by 40.8% to 52.4% compared to CRM, while achieving similar canopy deposition (0.92±0.57 µL·cm-2 for VRM vs. 1.13±0.57 µL·cm-2 for CRM) and coverage (42±3% for VRM vs. 52±6% for CRM). VRM also demonstrated more consistent deposition across both canopy and ground locations. Moreover, the ground deposition under target trees with VRM was much lower (0.17±0.10 µL·cm-2 and 4±3% coverage) than CRM (0.38±0.18 µL·cm-2 and 9±6% coverage). Multiple linear regression and Pearson correlation analyses indicated that wind conditions with average wind speeds in the range of 0.55 to 1.04 m s'¹ and wind directions between 130° and 229° were not able to significantly influence 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 variable-rate spray control system could potentially reduce chemical usage by 50% and reduce spray loss to the ground by 55% while maintaining comparable levels of spray deposition and coverage inside canopies. This new technology would be greatly beneficial to growers to minimize pesticide input into the production field and the environment.