Using Laser-Guided Variable-Rate Spray Technology with Reduced Rates to Control Pests and Decrease Off-Target Movement in a Tall Spindle-Trained Apple Orchard

Authors: MATTHEWS, LAUREN - University Of Tennessee; Hansen, Zachariah; LOCKWOOD, DAVE - University Of Tennessee; MCKIM, KARL - University Of Tennessee; LOPEZ, ELEANOR - University Of Tennessee; WRIGHT, WESLEY - University Of Tennessee; XIAOCUN, SUN - University Of Tennessee; Zhu, Heping; FULCHER, AMY - University Of Tennessee

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2025
Publication Date: 5/6/2025
Citation: Matthews, L., Hansen, Z.R., Lockwood, D., Mckim, K., Lopez, E., Wright, W., Xiaocun, S., Zhu, H., Fulcher, A. 2025. Using Laser-Guided Variable-Rate Spray Technology with Reduced Rates to Control Pests and Decrease Off-Target Movement in a Tall Spindle-Trained Apple Orchard. HortScience. 60(6):852-860. https://doi.org/10.21273/HORTSCI18464-25.
DOI: https://doi.org/10.21273/HORTSCI18464-25

Interpretive Summary: Apple producers in the United States rely on pesticide applications to protect crops from pests and diseases, requiring significant labor and material costs. Variable-rate technology uses sensors to detect the crop and travel speed and adjusts spray output in real time, eliminating application to voids between, under, below, and within trees. This reduces the volume of pesticide sprayed in a crop field compared to traditional air-blast orchard sprayers which are known to significantly over-apply pesticides with great off-target losses. This research evaluated spray characteristics and pest control efficacy of a laser-sensor guided sprayer operated in the variable-rate mode and compared it with the conventional, constant-rate spray mode. Spray modes were tested across two seasons at a commercial apple orchard located in Sevierville, TN. Pesticide volume was reduced by 58% in the variable-rate mode compared to the standard constant-rate mode, while pesticide coverage was maintained at or above industry standards to control pests and diseases. Overall, foliar and fruit disease and pest damage were maintained at low and commercially acceptable levels across both treatment modes. These results demonstrate the advantages of using laser-sensor guided variable-rate spray technology to decrease pesticide use and increase production efficiency in commercial apple orchards compared to standard practice.

Technical Abstract: US apple orchardists protect their crops from numerous insects and diseases using foliar pesticide applications in order to produce blemish-free produce and in doing so incur significant labor and input costs. Variable-rate spray application technology used at the default spray rate has successfully reduced pesticide volume, and consequently, input costs in orchards and nurseries while effectively controlling several diseases and insects. Our objectives were to evaluate spray characteristics and pest control efficacy of a sprayer operated in the variable-rate mode at a lower rate than the default rate and compare it with the conventional, constant-rate spray mode. Through preliminary experiments, a reduced spray rate of 0.05 L'm-3 of crop volume, which equated to 321.1 L'ha-1, was selected and compared to a conventional, constant-rate of 808 L'ha-1 by using a sprayer retrofitted with variable-rate spray technology and operated in the two different modes throughout two growing seasons. Foliage was scouted biweekly for diseases and two arthropods, and apples were scouted weekly for disease. Variable-rate mode reduced the pesticide volume applied by 58% while maintaining pesticide coverage at or above the overspray threshold in all but one canopy location. Non-target ground applications were greatly reduced in variable-rate mode. Foliar disease measured as leaf spot incidence and leaf spot count severity was not affected by spray mode. Fruit rot incidence, fruit rot severity, and disease index for fruit were also not affected by spray mode. Fruit disease index, which incorporates both incidence and severity measurements, remained low throughout both seasons. Disease progression was assessed by calculating the area under the disease progress curve (AUDPC). Foliar AUDPC was significantly higher in the variable-rate treatment at the middle of hill location, but not the bottom or the top of the hill, compared to the constant-rate treatment. Fruit AUDPC was not affected by treatment. While normally common in apple orchards, neither of the two arthropods were detected on any date. The utility and limitations of existing spray characterization metrics as well as the need for yet-to-be-developed metrics were discussed.