Spray Deposition, Drift and Equipment Contamination for Drone and Conventional Orchard Spraying Under European Conditions

In Europe, there is a growing interest in crop spraying using unmanned aerial vehicles (UAVs, drones), although current legislation imposes significant limitations on this technique. Spraying of orchard crops with drones remains particularly challenging due to the risks of spray drift and insufficient deposition uniformity. This study evaluated spray deposition within tree canopies (in two application terms), airborne and sediment drift losses, and contamination of the spraying equipment. The performance of a medium-sized drone (ABZ Innovation L10, maximum take-off weight 29 kg) was compared at flight speeds of 1.8, 2.7, and 3.6 m·s−1 with that of a conventional orchard sprayer (Munckhof axial sprayer with column attachment, operating at 1.7 m·s−1). A fluorescent tracer (BF7G, 1200 g·ha−1) was used in all trials, with spray volume rates of 27 or 40 L·ha−1 for the drone and 400 L·ha−1 for the sprayer. In most cases, deposition within the tree canopy was significantly lower for the drone. Poor uniformity of spray distribution was observed, especially between the upper and lower surfaces of collector plates with attached filter papers and between the top and bottom canopy zones. Airborne drift increased significantly with higher drone flight speeds, while sediment drift decreased. At 1.8 m·s−1, both drift types were comparable to those from the conventional sprayer. Drone surface contamination was several times lower than that of the ground sprayer, even when accounting for differences in equipment surface area.