The use of unmanned aerial spray systems (UASSs) for spot-spray applications is under investigation to control Popillia japonica clusters in vineyards. To evaluate and broad compare the UASSs performance for treatments on small-sized spots, the trials were carried out outdoor proposing a standardized methodology in absence of canopy vines and under controlled conditions. Polystyrene cubes hosting water sensitive papers (WSPs) on their faces were used as 3D collectors to measure the spray coverage (%) and stain density (No./cm2). The cubes were installed on vertical poles at two heights and aligned along the intended row(s) insisting on the spot. Two spot sizes were used, considering 1 and 3 potential vineyard row(s) insisting on them, and different flight paths were adopted accordingly. Conventional and drift-reducing nozzles were tested using the commercial UASS. Spray operational parameters were set to obtain 200 L/ha spray application rate per each spot. Results showed that spray coverage and stain density were not significantly influenced by the spot size and cube height. Conversely, significant interactions were found between the WSP positions on cube and nozzle type for the spray coverage, as well as both independent variables significantly affect the stain density without interaction. Better spray quality was measured for the top cube-face WSP, with conventional nozzle exhibiting the highest values (28% and 126 No./cm2). The lab-methodology enabled to investigate the UASS usability for small-size spot spraying in controlled conditions, providing reliable information on spray application performance related to the selection of UASS operational parameters.