Off-target spray drift deposition assessment from a knapsack application

With knapsack spray applications, off-target deposition of pesticide spray drift can be reduced by several means. The current research investigated the effects of drift-reducing nozzles, nozzle height, and nozzle shielding on spray drift deposition, using a combined approach involving modeling and experimental field trials. The drift deposition values derived from this study were compared with the regulatory values for different evaluation strips currently used for environmental risk assessments of pesticide applications in the European Union and United Kingdom. The results showed a strong impact of nozzle height on deposition at these evaluation strips. Drift-reducing nozzles reduced spray drift with at least their certified drift reduction class in almost all scenarios, and a nozzle shield additionally reduced spray drift. The combination of these three drift-reducing measures resulted in a decrease of spray drift deposition on the evaluation strips up to 99% as compared with the reference scenario. The results of the model calculations and field measurements were close for deposition values above the detection limit of the field trials. The current study provided realistic drift deposition values for a standardized band spray scenario, which can serve as higher-tier data to refine risk assessments for spot or band spray applications within the current authorization procedures for plant protection products in the European Union and United Kingdom.