## 1 Introduction
The main reason why this factor affects spray drift is the weight of the emitted drops: the bigger the size, the higher the weight and, therefore, the lower the drift, as the carrying effect of wind will be lower with heavier drops [34]. This was the way followed to develop drift-reducing hydraulic nozzles decades ago. These nozzles produce coarser droplets than the conventional ones do. This result is achieved either by (i) decreasing liquid pressure in the nozzles chamber (drift-guard (DG) nozzles) or (ii) by generating air-inflated drops (air-inclusion (AI) nozzles). As it is the most common strategy to reduce PPP drift, recently different studies have been focused to demonstrate that drift-reducing nozzles generate important spray savings while keeping the necessary spray deposition to ensure thebiological efficacy of treatments [44; 45]. Nevertheless, some farmers still prefer conventional nozzles as low-size drops generate higher coverage on the leaf surface. As a consequence [46], it is commonly believed they can achieve a higher efficacy against pest and diseases. Several studies have instead showed that droplet size could be increased to reduce spray drift risks without compromising the treatment efficacy [35; 47; 45], especially in unfavorable environmental conditions [48]. Pneumatic spraying is a well-known technique for its fine droplet size generation. As aforementioned, small droplets are generally requested by the farmers to achieve a uniform target spray coverage that is essential for contact PPP; thus, this technique is very widespread, especially among large-farm vine growers in America and Europe [49; 50]. In Italy there are large areas in which vineyard treatments are performed almost exclusively with pneumatic sprayers [51]. The small droplet size produced by this type of nozzle increases the drift risk with respect to the hydraulic nozzles [52]. Thus, whilst the droplet volume median diameter (VMD) generated by conventional hydraulic hollow-cone nozzles typically ranges from 100 to 200 \(\upmu\)m, for pneumatic nozzles the VMD is generally below 100 \(\upmu\)m [53; 54; 55]. This threshold of 100 \(\upmu\)m is broadly considered as the minimum diameter that droplets should have to reasonably limit the spray drift risk [56; 57]. Therefore, a droplet population with diameters below this value is subjected to losses by drift even with slow environmental air currents. In order to better understand the droplet population generated by pneumatic nozzles, [PERSON] et al. [53] investigated and quantified the effect of the main operational parameters, namely the liquid flow rate and the airflow rate, on different variables related to the droplet population, mainly their size and homogeneity. They also assessed the driftability of the drops according to the aforementioned parameters. In order to do so, they developed a laboratory test bench to simulate a real pneumatic sprayer and to test different combinations of parameters, measuring the droplet diameter with a laser device. Once the pneumatic spray behavior was well understood, the same authors planned a strategy to increase droplet size in case of high-speed environmental wind conditions [55]. The idea was to alter the liquid release position inside the air spout, taking advantage of the air speed decrease across the outermost section of the spout [55]. They obtained very promising results, recently confirmed by field trials [58], that demonstrated this strategy could have an important potential to properly reduce spray drift in pneumatic spraying thanks to the droplet size spectra increase. The main objective of this work was to develop, for the first time, drift-reducing spouts, namely cannon and hand spout types, for vineyard pneumatic sprayers. In detail we evaluated i) the possibility to increase droplets size by adjusting the water income position out of the nozzle spouts and ii) its effect on the droplet size population and homogeneity.