Horticultural Oil Thermotherapy Delivery System for Perennial Specialty Crops: A-Proof-of-Concept and Preliminary Results

Spray drift and residues of synthetic chemicals used in crop pest management are major concerns in agricultural industry. Therefore, exploration of alternative pest management technologies is necessary to minimize lasting pesticide residues without compromising biological efficacy. As such, this study reports the design and evaluation of a new horticultural oil thermotherapy (HOT) application system intended to increase biological efficacy of low-residue horticultural oils through addition of heat. A field-scale system has been constructed to apply thermotherapy onto tree fruit and berry crop canopies. This system uses a custom heating unit to preheat the spray liquid, reaching the nozzles at temperatures up to 99°C depending on application requirement. The spray delivery and temperature profiles generated by the prototyped HOT system were evaluated at three horizontal distances from the nozzle exit (0.6, 1.5, and 2.1 m) using a smart spray analytical system developed by our research group. Typical to tree fruit sprayers, higher spray delivery was collected at 0.6 m distance and trended to decrease with increasing distance from the nozzles. The spray plume temperature also decreased with increasing distance from the nozzle. The prototype was evaluated in a pear orchard providing adequate spray coverage at bottom (75% average at 1.2 m AGL) and middle (53% average at 2.4 m AGL) canopy zones. However, the coverage in the top canopy zone (3.6 m AGL) was less than 8% and will require adjustments to the nozzle assembly. Overall, configuration refinements and calibration adjustments will be required in the prototyped HOT system depending on the crop growth stage and canopy architecture for optimal application efficacy. The developed system, with due optimization, will be critical in providing evidence supporting the feasibility of HOT applications.