Effects of flight height, flight speed and spray volume of a UAV based spraying system on droplet deposition in cashew trees

• For the first time, effects of flight height (FH), flight speed (FS) and spray volume (SV) of a UAV based spraying system on spray performance in cashew orchard was investigated. • FS, FH and SV had a significant effect on all the studied parameters of spray performance. • The effects of FS, FH and SV on spray performance were in the order of FS > SV > FH, FS > SV > FH, FH > SV > FS, FS > FH > SV, respectively. • The most optimal combination for spray performance was flight speed 3 m/s, height 7 m, and spray volume 60 L/ha. Cashew is an important commercial tree cultivated for its edible nuts. In cashew, mainly the tractor-operated airblast sprayers and High-pressure triplex (HTP) power sprayers are used for agro-chemicals applications. These methods are inefficient, and pose risks to operators, especially in high-density planting orchards. Recently, Unmanned Aerial Vehicles (UAVs) or drones are drawing attention in spray applications for tree crops as they offer high spray efficiency, and reduce risk of environment and operators. However, effects of spray parameters of drone on the droplet distribution and off-target losses in cashew orchard have remained unexplored. In the present study, spray experiments were conducted in cashew orchard using hexacopter drone with Box–Behnken design (BBD) for three factors [flight speed (FS), flight height (FH), and spray volume (SV)] at three levels forming a total of 17 treatments. The spray performance of the UAV was evaluated based on response variables viz., volume mean diameter (VMD), droplet density (DD), droplet deposition penetration (DDP) and droplet distribution uniformity (DDU) by using water sensitive papers combined with an image processing software. The results showed that FS, FH and SV had a significant effect on all the studied parameters (p<0.001). The effects of three factors on VMD, DD, DDP, DDU were in the order of FS > SV > FH, FS > SV > FH, FH > SV > FS, FS > FH > SV, respectively. The optimal combination for spray performance was FS2-FH1-SV3 (flight speed 3 m s -1 , height 7 m, and spray volume 60 L ha -1 ) having a VMD of 308.48 µm, DD of 57.28 drops/cm², droplet penetration of 44.57%, and distribution uniformity of 77.21%. The results of this study showed the great potential of UAVs in enhancing the spray efficiency and sustainability of crop protection in cashew orchards and provides valuable data for future innovation in this area.