Foliar deposition and off-target loss in young apple orchard with PWM-controlled spray systems

Authors: Zhu, Heping; OZKAN, ERDAL - The Ohio State University; SALCEDO, RAMON - The Ohio State University; Jeon, Hongyoung; FLACHIERI, DAVIDE - Innovation In Crop Protection

Submitted to: Aspects of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2022
Publication Date: 4/10/2022
Citation: Zhu, H., Ozkan, E., Salcedo, R., Jeon, H., Flachieri, D. 2022. Foliar deposition and off-target loss in young apple orchard with PWM-controlled spray systems. Aspects of Applied Biology. 147:149-155.

Interpretive Summary: The pulse width modulation (PWM) technology has been used in both conventional constant-rate and intelligent laser-guided variable-rate orchard sprayers to control spray outputs for delivery of pesticides. However, there is very little research conducted in young tree orchards to document how far spray droplets can travel beyond the first sprayed row, and how much spray is lost to the ground and in the air. In this research, spray deposition quantities and spray losses were evaluated in young apple orchards with an intelligent PWM spray system, a manual-controlled PWM spray system and a conventional constant-rate system. Test results showed the intelligent spray system used 67% less spray volume than the manual-PWM system and 76% less than the conventional spray system. The intelligent spray system had such great volume reductions because it stopped spraying gaps between trees and its spray outputs were automatically adjusted based on the individual tree foliage volume. Also, compared to the conventional system, the intelligent system reduced the total airborne drift by 90.3% and total ground loss by 85.0% while the manual-PWM system reduced the total airborne drift by 84.1% and ground loss by 7.9%. Moreover, the spray systems equipped with the PWM control technology could have sufficient deposition on young trees by spraying every other row or even three rows instead of spraying every row, so as to save pesticide and application time with minimized risk of polluting the environment. Thus, orchard sprayers equipped with PWM technology would significantly improve spray application efficiency with great reductions in pesticide use and off-target loss in young apple orchards.

Technical Abstract: Pulse width modulation (PWM) technology has been recently introduced into constant-rate and variable-rate orchard sprayers to improve pesticide application efficiency. In this research, two different PWM spray systems were integrated in a reference air-blast sprayer for comparisons of foliar spray deposition quantity and potential reduction in off-target losses in orchards with young trees. The two systems were a manual PWM -controlled constant-rate system and a laser-guided PWM-controlled variable-rate system. The same laser-guided spray system was also used with deactivation of PWM valves to produce a conventional constant-rate application as reference for the tests. The PWM technology improved application efficiency to treat two or more rows of trees with a single spray pass, and also reduced variations in the relationship between foliar deposition and spray drift loss. Compared to the conventional constant-rate spray system with comparable foliar deposition quality, the laser-guided spray system reduced the total airborne drift by 90.3% and total ground loss by 85.0% while the manual-controlled PWM system reduced the total airborne drift by 84.1% and ground loss by 7.9%. However, the laser-guided spray system used 67% and 76% less spray volume than the manual-controlled PWM system and the conventional constant-rate spray system, respectively. The research findings suggested that growers could use the new technology to spray two or more rows of young trees simultaneously with a single spray pass to reduce pesticide use, save spray time, and minimize the off-target damage to the environment.