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

Abstract

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.

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

“…Therefore, both models (that for cannon‐type and that for hand‐type nozzles) seem to explain almost every change in the D50 parameter. Of major importance when advising applicators who have to control droplet size in their treatments, especially when the environmental wind speed is notorious, is droplet size, which is a major concern from the drift point of view . The two fitted models are consistent with the data represented in both graphics (Fig.…”

“…According to Hofman and Solseng the factors affecting pesticide emissions to the air during the application process can be divided into technical and environmental factors (weather conditions at the time of application, namely wind speed and direction, temperature, relative humidity and stability of the air at the application site). Among the technical factors, the size of the particles has a large impact on the off‐target drift: fine spray tends to increase the drift risk . At the same time, the effect of droplet size and spray volume rate on spray deposit and coverage, which determine the technical performance and biological efficacy of spray applications in fruit crops, is recognized as crucial.…”

“…Excessive fan air volumes have also been reported to increase drift losses in apple orchards, in vineyards and in young high tree plantations . At the same time, the right adjustment of air jet (air flow rate and air direction), depending on the canopy size, leaf density, and row distance, resulted in spray drift reduction and deposition increase …”

“…When operating with hydraulic nozzles, the main available strategy to reduce spray drift is the use of air induction nozzles, which proved to substantially reduce the spray drift, compared to conventional nozzles, by maintaining similar deposition values and, in this way, ensuring consistency in the biological efficacy of treatments . On the other hand, to date no innovative environmentally friendly commercial solutions are available for pneumatic sprayers on the market.…”

Toward a new method to classify the airblast sprayers according to their potential drift reduction: comparison of direct and new indirect measurement methods

“…It provides results that are highly affected by external factors like environmental conditions during testing . Moreover, direct drift experiments that compare different spray systems cannot be performed under identical environmental conditions and crop structures . While ISO 22866 is useful to obtain information on the drift ability of a specific sprayer configuration and on the amount of drift generated within a specific crop context, the wide variation of environmental conditions and crop structures makes it unsuitable for establishing any broad ranking or classification of spray drift reduction technologies (SDRT) .…”