Foliar deposition and coverage on young apple trees with PWM controlled spray systems

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

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2020
Publication Date: 10/1/2020
Citation: Salcedo, R., Zhu, H., Zhang, Z., Wei, Z., Chen, L., Ozkan, E., Falchieri, D. 2020. Foliar deposition and coverage on young apple trees with PWM controlled spray systems. Computers and Electronics in Agriculture. 178. Article 105794. https://doi.org/10.1016/j.compag.2020.105794.
DOI: https://doi.org/10.1016/j.compag.2020.105794

Interpretive Summary: In apple orchards, spray applicators usually select a constant rate to apply chemicals with little consideration of tree canopy characteristics and planting patterns. This practice is inefficient and has caused excessive use of pesticides, which becomes even much worse for young trees. The pulse width modulation (PWM) technology has been recently incorporated into constant-rate and variable-rate orchard sprayers to maintain the required spray pattern to achieve significant reductions in pesticide waste. In this research, three different PWM spray systems were integrated in the same reference sprayer to treat young apple tree crops. The three systems were: a manual-controlled PWM system generating a constant-rate application, a laser-guided PWM-controlled variable-rate spray system, and the same laser-guided spray system with PWM valves disabled to produce a constant-rate application. Spray deposition quantities with the three PWM spray systems were compared to determine if a single spray pass would provide adequate spray deposition and coverage on young apple trees in the first and downwind rows. Test results demonstrated the increased efficiency of spray systems equipped with the PWM technology for spray applications in young apple orchards. A single spray pass with the three spray systems could achieve an adequate amount of spray deposits and coverage on trees in the first two rows for fungicide applications and four rows for insecticide applications. Compared to the disabled PWM system, the manual-controlled PWM system and the laser-guided PWM system reduced the application rate by 27% and 76%, respectively. Thus, sprayers equipped with the PWM technology could reduce production costs and reduce the number of spray passes required for effective pest control in young apple orchards while the laser-guided PWM system presented the most efficient method to save chemical costs and minimize environmental risks.

Technical Abstract: Pulse width modulation (PWM) technology is recently introduced into orchard air-blast sprayers to achieve precision applications of plant protection products and reduce risks to the environment and ecosystems. Field tests in a two-year old apple orchard were conducted to evaluate spray deposition quality of three systems attached to an air-blast orchard sprayer: 1) a manually-PWM-controlled spray system producing a constant-rate application (Manual-PWM), 2) a laser-guided PWM-controlled intelligent spray system producing a variable-rate application (Laser-PWM), and 3) the same laser-guided spray system with disabled PWM control producing a constant-rate application (Disabled-PWM). Spray deposition distributions on multiple-row trees were quantitatively evaluated for the three spray systems. Test results showed that the Manual-PWM and Disabled-PWM produced greater leaf deposits and coverage with over-sprayed potentials on the first row trees than Laser-PWM. However, spray coverage results indicated that Laser-PWM provided higher uniformity across the tree canopy and a stronger relationship between spray deposits and coverage for all the rows than other two systems. Moreover, Laser-PWM used 67% and 76% less spray volume than Manual-PWM and Disabled-PWM, respectively. Test results also demonstrated that spray deposit densities on trees in the first two rows discharged from all three spray systems exceeded thresholds for effective fungicide and insecticide applications. A single spray pass from each of the three systems could provide adequate spray deposits and coverage on the two-year old young trees in the first two rows, thereby offering opportunities to save pesticides and reduce labor costs.