Intelligent sprayer spray rates optimization to efficiently apply chemicals in modern apple orchards

Authors: RATHNAYAKE, A - Washington State University; SAHNI, R - Washington State University; KHOT, L - Washington State University; HOHEISEL, G - Washington State University; Zhu, Heping

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2022
Publication Date: 10/10/2022
Citation: Rathnayake, A.P., Sahni, R.K., Khot, L.R., Hoheisel, G.A., Zhu, H. 2022. Intelligent sprayer spray rates optimization to efficiently apply chemicals in modern apple orchards. Journal of the ASABE. 65(6):1411-1420. https://doi.org/10.13031/ja.14654.
DOI: https://doi.org/10.13031/ja.14654

Interpretive Summary: The efficacy of spray treatment with air-assisted sprayers in apple orchards is dependent on several factors including sprayer configuration parameters, chemical compatibility, weather condition, and orchard characteristics. The application rate, the amount of liquid sprayed, is one of the primary factors for achieving best pest control in the vertically structured perennial crops. However, there is no consensus on a single method to decide application rates until the intelligent spray technology is developed. In this research, input spray rates estimated by the tree-row-volume and unit crop row methods were investigated for future practices of the intelligent orchard sprayers with variable-rate applications in modern apple orchards. The spray deposition and coverage data showed similar or better spray efficiency compared to the constant 935 L ha-1application rate commonly adapted by growers for conventional orchard sprayers. The test results demonstrated the suitability of both methods to estimate spray rates for future spray applications with intelligent air-blast sprayers in western apple orchards trained in fruiting wall at fully foliated canopy growth stage.

Technical Abstract: The efficiency of air-assisted sprayer based chemical applications in horticultural crops is dependent on several factors including that of the application rate as the amount of liquid per ground area (L ha-1 or gal acre-1 [GPA]). In contrast to the conventional GPA based application rates, recently developed intelligent and precision sprayers use the input spray rate (SR) as the amount of liquid volume (L) required to spray one cubic meter of crop canopy (L m-3 or ounces per cubic feet). This input rate ranges between 0.09 and 0.13 L m-3 depending on the architecture and canopy size. However, exact value of input SR is decided based on growers’ experience and manufacturer recommendation and often can be a broad estimation. Therefore, this study was conducted to explore methods that could be used to have precision estimate of the input SR related to canopy being sprayed for optimal spray applications. Tree row volume (TRV) and unit canopy row (UCR) methods were used to estimate input SRs and the sprayer efficiency was evaluated in a vertical fruiting wall trained commercial apple orchard, typical in the Washington State, USA. The amounts of spray deposition and spray coverage at various positions inside tree canopies were quantified for TRV and UCR and were compared with the grower adapted application rate (935 L ha-1). Test results demonstrated that both TRV (SR: 0.09 L m-3) and UCR (SR: 0.10 L m-3) had comparable spray deposition and coverage to the grower adapted application rate. While the spray rates calculated by both methods provided better application efficiency, adjustments to these estimates and crop specific further evaluations were suggested for different canopy training systems.