Reducing ground and airborne drift losses in young apple orchards with PWM-controlled spray systems

Authors: SALCEDO, RAMON - The Ohio State University; Zhu, Heping; OZKAN, ERDAL - The Ohio State University; FALCHIERI, DAVIDE - Innovation In Crop Protection; ZHANG, ZHIHONG - Kunming University Of Science And Technology; WEI, ZHIMING - Shandong Academy Of Agricultural Sciences

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2021
Publication Date: 8/21/2021
Citation: Salcedo, R., Zhu, H., Ozkan, E., Falchieri, D., Zhang, Z., Wei, Z. 2021. Reducing ground and airborne drift losses in young apple orchards with PWM-controlled spray systems. Computers and Electronics in Agriculture. 189. Article 106389. https://doi.org/10.1016/j.compag.2021.106389.
DOI: https://doi.org/10.1016/j.compag.2021.106389

Interpretive Summary: In apple orchards, constant rates are commonly used to apply chemicals with little consideration of tree canopy characteristics and planting patterns. This practice is inefficient and has led to excessive pesticide waste through off-target loss to the ground and airborne spray drift in the air. The waste is even greater for applications in orchards with younger trees. The pulse width modulation (PWM) technology has been recently incorporated into conventional and intelligent orchard sprayers to improve pesticide application efficiency. In this research, two different PWM spray systems were integrated in the conventional sprayer to treat young apple trees. The two systems were a manual-controlled PWM system generating a constant-rate application, and a laser-guided intelligent spray system to automatically provide variable-rate applications. They were tested for the potential reductions in off-target losses in orchards with young trees. Compared to the standard 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 standard constant-rate spray system, respectively. 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. Thus, the research finding suggested that growers could use the new technology to spray two or more rows simultaneously with a single spray pass to reduce pesticide use, save spray time, and minimize the off-target damage to the environment.

Technical Abstract: Pulse Width Modulated (PWM) solenoid valves can be used to control nozzle flow rates for precision spray applications to reduce pesticide use, thereby reducing environmental risk and production cost. Field tests in a two-year-old young apple orchard were conducted to investigate spray losses to the ground and in the air for an air-blast sprayer equipped with three spray systems: 1) manually controlled constant-rate system enabled with the PWM spray system (Manual-PWM), 2) laser-guided variable-rate system enabled with the PWM spray system (Laser-PWM); and 3) conventional constant-rate system with disabled PWM valves (Disabled-PWM). Artificial targets (plastic plates and water sensitive papers) were placed under twelve trees randomly selected from four rows of the orchard to collect spray losses to the ground. Airborne spray losses were determined by using nylon screens, mounted at five heights on each of seven poles distributed at different distances from the first sprayed row. Laser-PWM and Manual-PWM produced significantly lower airborne and ground spray drift losses inside and outside the orchard than Disabled-PWM, and these losses decreased significantly as the distance away from the first sprayed row increased. Laser-PWM reduced the total airborne drift by 90.3% and total ground loss by 85.0% compared to Disabled-PWM whereas Manual-PWM decreased the same airborne and ground drift by 84.1% and 7.9%, respectively. Disabled-PWM produced detectable airborne losses that reached 88.4 m away from where the sprayer was operated. Thus, the air-blast orchard sprayer equipped with PWM solenoid valves controlled by either automatic laser-guided system or manual system would have great potentials to improve pesticide application efficiency with significant reductions in both pesticide consumption in young apple orchards, and off-target drift loss to the environment.