Comparative Spray Performance of a Solid Set Canopy Delivery System and an Airblast Sprayer in Modern Apple Orchards

Highlights Airblast sprayer applications in modern apple orchards can produce high off-target drift. A pneumatic spray delivery based solid set canopy delivery system (PSD-SSCDS) can be an alternative solution. PSD-SSCDS had comparable spray deposition, but lower spray coverage compared to airblast sprayer. Airblast sprayer had significantly higher losses to the ground and aerial drift. PSD-SSCDS confined ground drift within 4.1 m with minimal spray losses to air. Abstract. A pneumatic spray delivery-based solid set canopy delivery system (PSD-SSCDS) has been successfully configured for efficient spray applications in modern apple orchards typical of the state of Washington state. This study investigates the spray performance of optimized PSD-SSCDS against an axial-fan airblast sprayer in terms of spray deposition, coverage, and off-target drift in a tall spindle architecture of a commercial apple orchard. For field evaluation, mylar cards and water sensitive paper samplers were placed in different canopy zones on either side of the leaf surface, and 500 ppm of biodegradable fluorescent tracer solution was sprayed with PSD-SSCDS and an airblast sprayer. Additionally, aerial and downwind samplers were installed to evaluate ground runoff and drift, as well as aerial drift. The spray deposited on the mylar cards was analyzed using fluorometry, and spray coverage on WSPs was evaluated using image processing techniques. PSD-SSCDS (645.0 ± 94.7 ng cm -2 , mean ± standard error) and an airblast sprayer treatment (661.6 ± 26.9 ng cm -2 ) had comparable mean spray deposition with no significant difference in different canopy zones for both treatments. However, the spray coverage was significantly higher for the airblast sprayer (32.7 ± 2.4%) compared to PSD-SSCDS (22.5 ± 3.1%). These differences are likely due to air-assist in airblast spraying, which is absent in PSD-SSCDS. Evidently, the airblast sprayer had significantly higher losses to the ground and aerial drift compared to PSD-SSCDS, as the ground drift for the latter was mostly confined within 4.1 m downwind of the sprayed row and spray losses to air were minimal. Keywords: Crop protection, Fixed spray delivery, Off-target drift, Pneumatic spray delivery, Spray coverage, Spray deposition.