Ground Deposition and Airborne Spray Drift Assessment in Vineyard and Orchard: The Influence of Environmental Variables and Sprayer Settings

Spray drift assessment encompasses classification of the capacity of each sprayer/ technology/setting combination to reduce or avoid the spray drift risk, as well as drift measurement to define buffer zones mandated during pesticide application. Compounding the challenge of these tasks is the great variability of field evaluation results from environmental conditions, spray application technology, canopy structure, and measurement procedures. This study, performed in Spanish context, evaluates the effects of different parameters on comparative measurements of ground and airborne spray drift employing the ISO22866:2005 protocol. Four configurations of air blast sprayers, derived from two fan airflow rates and two nozzle types (conventional and air-induction), were tested in orchard and vineyard at late growth stage. Spray drift curves were obtained, from which corresponding Drift Values (DVs) were calculated using an approximation of definite integral. Both sprayer settings and environmental variables statistically affect spray drift total amounts and result variability. PCA analysis showed that nozzle type and wind speed characteristics explained 51% and 24% of the variance, respectively. In particular, mean wind direction influence ground sediments (Pr < 0.01) and maximum wind speed strongly influence airborne drift value (Pr < 0.0001). The wind characteristics concealed the influence of adopted fan airflow rates on final spray drift assessment results. The effect of uncontrollable environmental conditions makes objective and comparative tests difficult.