Assessing the influence of air speed and liquid flow rate on the droplet size and homogeneity in pneumatic spraying.

BACKGROUND: The efficacy of treatments in vineyards largely depends on the necessary balance between leaf coverage and spray drift and, therefore, knowledge about droplet size is of major importance, but scarce scientific information is available on pneumatic spraying, often adopted in this crop. The objective of this work was to obtain the relationships between the droplet size spectra characterization parameters and themain affecting factors in pneumatic nozzles. RESULTS: Three liquid flow rates (LFR) and four air speeds (AS) were combined in laboratory conditions to assess their influence on the droplet size spectra (D10, D50 and D90), homogeneity (Relative Span Factor, RSF) and driftability (V100) in two different air shear nozzles (cannon-type and hand-type nozzles). The droplet size parameters were significantly affected by LFR and AS, and a model was fitted to predict droplet size in every spout type. The droplet V100 was also affected by both factors. The RSF was similar in both cases but did not follow regular trends. CONCLUSIONS: The findings obtained can help vineyard farmers and technicians to effectively increase the efficiency and, therefore, the efficacy of the pesticide treatments reducing at the same time the spray drift risk by selecting appropriately the optimal values of themain operational parameters: LFR and AS.