Abstract
A study was conducted to characterize the general features of splash droplets produced from impacting raindrops in an effort to better understand rain splash dispersal of fungal plant pathogens. A rain generator was used to produce simulated raindrops, with a distribution of drop sizes which was very similar to natural rain, that impacted on different ground covers or strawberry plants through a 100-cm 2 opening of a rain shelter. Three ground covers, i.e. soil, straw, and plastic mulch, were tested with simulated rains of 15 and 30 mm h −1 intensity. Effect of plant density was also evaluated by placing strawberry plants of different leaf area indices in the exposed area of the rain shelter. Water sensitive papers were used to collect splash droplets in order to determine droplet size distribution, number and mass flux densities over distance from the raindrop impact area, and also mass reflection. The distribution of splash droplet size was found to be highly and positively skewed and was well fitted by the Weibull distribution function. The median size of splash droplets was less than 0.26 mm in diameter, and the Weibull parameters were largely independent of rain intensity. Both flux densities of splash droplet number and mass declined with distance from the window edge, and were represented by an exponential gradient model. The steepness of the gradients was found to increase with surface roughness (i.e. steepest for straw, shallowest for plastic), and decrease with rain intensity. Mass ratio of the splash droplets to the incident raindrops was in the range of 0.29 to 0.38 without the presence of strawberry plants, and was affected by ground cover, rain intensity, and their interaction. With raindrop impactions on plants, mass reflection was greatly reduced to 0.02–0.09. Results were consistent with, and help explain, the previously demonstrated relationship between surface topography and splash dispersal of fungal spores.
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