Experimental study of factors influencing the risk of drift from field sprayers, Part 1: Meteorological conditions.

Spray drift can be defined as the quantity of plant protection product that is carried out of the sprayed (treated) area by the action of air currents during the application process.  This continues to be a major problem in applying agricultural pesticides. The purpose of this research is to measure and compare the amount of drift for different climatological conditions under field conditions.  Sedimenting spray drift was determined by sampling in a defined downwind area at different positions in a flat meadow using horizontal drift collectors for a reference spraying.  Meteorological conditions were monitored during each experiment.  A drift prediction equation for the reference spraying was set up to predict the expected magnitude of sedimenting drift at various drift distances and atmospheric conditions.  The measurements proved the important effect of weather conditions (temperature, relative humidity and wind speed) on the amount of spray drift. A lower wind speed or a higher relative humidity decreases the amount of spray drift.  Taking into account the correlation between temperature and relative humidity, a lower temperature will also result in lower drift values due to the cumulative effect of relative humidity.  This equation can be used to quantify the effect of meteorological conditions, to compare measurements using other spraying techniques under different weather conditions to the reference spraying and to perform spray drift risk assessments.