Identifying droplet size predictors of spray drift using wind-tunnel droplet tracking

Authors: BATISTA DE OLIVEIRA, RONE - State University Of Northern Paraná (UENP); RODRIGUES DA CUNHA, JOAO PAULO - Federal University Of Uberlandia; Zhu, Heping; Jeon, Hongyoung

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2026
Publication Date: 4/25/2026
Citation: Batista De Oliveira, R., Rodrigues Da Cunha, J.A., Zhu, H., Jeon, H. 2026. Identifying droplet size predictors of spray drift using wind-tunnel droplet tracking. Crop Protection. Article 107661. https://doi.org/10.1016/j.cropro.2026.107661.
DOI: https://doi.org/10.1016/j.cropro.2026.107661

Interpretive Summary: Spray drift remains a major concern for regulators and farmers due to its risks to farming safety, community health, and crop protection effectiveness. Although several indicators have been used for prediction of spray drift potentials, their practical sensitivity and reliability are uncertain. In this research, droplet size parameters were investigated as potential spray drift predictors in a controlled wind tunnel environment. Investigations included spray drift of various sized droplets produced from different types of nozzles under various wind conditions. Test results revealed that volume median diameter and volume fraction of droplets smaller than 150 µm were the most reliable predictors among spray parameters evaluated. This framework would provide a new approach for researchers, manufacturers, farmers and regulators to refine spray drift assessment and enhance crop protection efficiency. It would also assist farmers to predict spray drift risks ahead of pesticide applications to minimize farmland contamination and neighboring crop injuries.

Technical Abstract: Predicting spray drift using droplet size parameters is not well understood, especially encountering with varying wind speeds and downwind distances. Although some indices have been proposed, their sensitivity and reliability for drift assessment remain unclear. The objectives of this research were to evaluate drifted droplet sizes at various downwind distances and determine different droplet size parameters as spray drift predictors by analyzing the movement of spray droplets inside a wind tunnel under various wind speeds and nozzle types. Experiments used a laser diffraction system to measure droplet size distributions at distances of 1, 2, 3, 4, and 5 m downwind from the nozzle within a wind tunnel featuring a 2 m × 2 m × 7.5 m test section. These measurements involved with four nozzles (TXA8002, TXA8004, XR11002, and XR11004) tested under wind speeds of 2, 3, 4, 5, and 6 m·s-1. Key metrics included Dv10, Dv50, Dv90, the Relative Span index (RSI), and the volume percentage of droplets smaller than 100 µm (V100), 150 µm (V150), and 200 µm (V200). Test results identified Dv50 and V150 as the most reliable indicators for predicting spray drift potential, while V200 and RSI showed limited value under different wind conditions and drift distances. This pattern was consistent regardless of the type of nozzle. This spatial analysis of droplet movement proved robustness in identifying key factors that influence spray drift, offering a valuable framework to optimize nozzle selection and operational conditions, ultimately reducing drift risks and improving application efficiency and environmental safety.