Wind tunnel measurements to determine the efficiency of drift control agents

Spray drift is defined as the quantity of plant protection product that is deflected out of the treated area by air currents at the moment of spray application. Drift deposition outside the target field can have negative effects on the health of humans and the environment, and it also leads to economical losses. Spray drift is affected by 4 main factors: weather conditions, spray application technique, surrounding characteristics and physicochemical properties of the spray liquid. This research focuses on the importance of physicochemical properties (surface tension, viscosity, evaporation rate and density) of spray liquids on drift.
Drift control agents are typically polymer adjuvants that increase the viscosity of the spray mixture, and therefore increase droplet size of the spray. Coarse droplets are known to be less drift-prone than fine ones.
Most researchers, that examined the drift-reducing effects of adjuvants, used solutions of the adjuvant in water, while it is generally known that not the physicochemical properties of the adjuvant itself, but the physicochemical characteristics of the complete spray mixture (pesticide formulation + adjuvant) are drift-determining.
In this research, adjuvant/formulation combinations are examined, in stead of using an adjuvant/water system.
The set-up of the research is discussed. In a first part, laboratory tests are performed to measure surface tension, viscosity, evaporation rate and density of the spray liquid formulation, with and without the addition of the drift control agent. Subsequently drift experiments are performed in the wind tunnel of the International Centre for Eremology (I.C.E.) at Ghent University, Belgium.