New Methods Using Simulated Rain to Study the Splash Dispersal of Plant Pathogens

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Abstract
Methods were developed for studying the effect of simulated rain on splash dispersal of fungal plant pathogens. Spray nozzles were mounted on a horizontal boom that was rotated at 2 rpm by a motorized chain-drive assembly. Water volume distribution was found to be about uniform within a 1-m2 target area. Low, medium-, and high-volume spray nozzles produced water-drop volume distributions that closely approximated natural rains with intensities of 15, 30, and 60 mm/hr, respectively. A test of the rain simulator was conducted using spread of leather rot of strawberries [Phytophthora cactorum] as a model disease system. Potted strawberry plants were arranged in concentric circles within a specially constructed wood frame. Ten infected strawberry fruits, placed at the center of the circle of plants, served as the inoculum source. ANOVA results demonstrated that percentage of fruit infection differed significantly in response to rainfall intensity, distance of plants from inoculum, and position of fruit within a plant crown (P = 0.05). The only significant interaction was distance by position. Mulch generally reduced infection, but this effect was not significant (P = 0.05).