Micrometeorological and operational factors affecting ultra-low-volume spray application of insecticides onto cotton and other crops

Abstract

The effect of micrometeorological variables on the travel and deposition of small droplets employed in ultra-low-volume (ULV) crop spray application has been examined in trials in Malawi. Continuous recording of meteorological factors has enabled the determination of the Richardson number, friction velocity, also intensity of turbulence characterised by coefficient of variation of wind speed measured in the horizontal plane. Spray trials have been carried out under well defined conditions in which sampling of droplets has been effected on horizontal (upward and downward aspect) and vertical (windward and leeward aspect) targets both above and within the crop (cotton and groundnuts) or over bare ground, at logarithmic intervals downwind of an approximate line source of spray (using the Micron ULVA hand sprayer carried across the wind at a predetermined height relative to the canopy and spraying a waterless ULV insecticide formulation). Counts have been made of droplet density (no. cm −2) and the net collection on horizontal upper and windward vertical surfaces has been ascertained. Correlation between droplet collection in various positions and meteorological variables (singly and in combination) has been examined. Best correlation is obtained from a combination of variables which differs according to the position of the target site.