A systematic literature review on recent unmanned aerial spraying systems applications in orchards

In a context of global population growth, modern agriculture is required to optimize crop production efficiency. Precision agriculture (PA) can contribute to this by optimizing production and quality standards. PA has implemented the use of advanced technologies such as unmanned aerial system (UAS) that enable the implementation of resource use efficiency. UAS due to their feasibility and versatility, play a key role in orchard monitoring and plant protection product (PPP) distribution. The aim of this review is to explore the crucial role of unmanned aerial spraying systems (UASS) as innovative tools to optimize management, resource efficiency and sustainability of orchards. The review involved the analysis of a range of studies published in the period of 2019-2024. This study provides a comprehensive review of the scientific literature, focusing on the effect of aerial spray drift, considering the main parameters that could influence the application of PPP with UASS. A comparison of the operational parameters of UASS and their different configurations was examined in depth. The efficiency of droplet deposition quality of UASS on different canopy layers of trees was also examined, exploring the findings of these systems in orchards. The comparison between UASS and traditional orchard spraying methods was explored, and global legislative regulations and future perspectives were discussed. The literature highlights that using a flight height of 2 m above the canopy level (ACL), the downwash effect ensures efficient deposition of PPP while effectively limiting drift. The results show that approximately 60% of UASS spraying treatments in orchards use hydraulic nozzles, significantly more common than centrifugal nozzles. The 4-rotors UASS performed better than the 6-rotors and 8-rotors UASS in terms of deposition efficiency due to the 1.5 m working width corresponding to the canopy diameter, minimizing drift and ground losses while optimizing lateral coverage. Although UASS application of PPP still has to overcome several challenges, the review highlighted the importance of aerial spraying applications in orchards and the huge potential of this technology.