Assessing the potential efficacy and efficiency of UASS vine-targeted spray application across growth stages

Optimising of operational parameters of unmanned aerial spray systems (UASSs) remains a challenge for row crops. This paper presents the results of field trials conducted in a vineyard (Vitis vinifera cv. Ruché) using an innovative customised spray system, equipped with hollow-cone prototype nozzles (conventional and air inclusion) with a narrow 30° spray angle, mounted on a DJI Matrice 600 Pro. One way-band flights were done above a vine row at two UASS flight speeds (1.5 and 3.0 m s−1) across early, middle, and late vine growth stages. Canopy deposit, in-field ground losses, spray quality (coverage and deposit density), and spray application efficiency were measured to evaluate the tested parameters effects. Results showed that canopy deposit was mainly affected by the growth stage (14 % more deposit in late stage with respect to early), whereas the operational parameters influenced the spray quality and its vertical homogeneity in the canopy. Spray application efficiency depended on the interaction between growth stage and nozzle technology with conventional nozzles performing better at the early stage (14 % more), while air inclusion nozzles outperformed at the late stage (32 % more). The 1.5 m s−1 UASS flight speed improved coverage uniformity even if canopy deposits gains were modest. A not negligible spray amount reached the ground (at least 50 %). Through a cross-study benchmark versus 60° nozzles, it was observed that pairing a 30° angle with air inclusion nozzles doubled canopy deposit (+100 %), whereas 30° conventional nozzles reduced canopy deposit (-37 %) and increased ground losses (+87 %).