Influence of weed leaves surface structures on droplet spread and evaporation

In order to reveal the difference in droplet spread and evaporation of the weed leaves with different surface structures, a series of experiments were conducted in this paper. The spray liquid was 0.5% glyphosate, the additive was organic silicon in a series of concentrations, and the sizes of tested droplets were 228 and 288 μm. The tested weed leaves had three surface structures, namely hairy, waxy and rough. The experimental evaporation process was recorded by a digital camera, so that the evaporation time and the image of maximum droplet spread area could be read from the video. The digital images of maximum spread area were segmented by using the Image Processing Toolbox of Matlab; eventually the size of the spread area was obtained. The experiment results indicated that increasing additive concentration led to an expanded spread area and a reduced evaporation time for the same leaf and droplet size. For the same droplet size and additive concentration, hairy leaves showed a largest spread area and a shortest evaporation time. The additive concentration exhibited most significant influence on spread and evaporation time when a droplet was on a leaf with waxy surface. For a leaf with rough surface, the grooves on the surface made the droplets in small size be spread relatively hard; for the droplets in large size, however, the groove structure showed less dominated effect on the spread area.