A portable rainfall simulator for evaluating the wet deposition of plant pathogens

A portable, single nozzle rainfall simulator was designed for evaluating the wet deposition of plant pathogens within field crop canopies. The simulator consisted of a black iron and galvanized pipe frame with a single nozzle (24WSQ or 50WSQ) centered at least 3 m above the upper plant canopy surface and had an attachment that allowed for fungal spores to be injected into the simulated rainfall. At the operating nozzle pressure of 34.5 kPa, the water volume distribution was relatively uniform (coefficients of uniformities of 85% and 86%) within the 2- × 2-m sample area. Drops ranged in size from 0.2 to 3.3 mm with median drop diameters of 1.0 mm for the 24WSQ nozzle and 1.6 mm for the 50WSQ nozzle. The measured rainfall intensities were 45 and 85 mm h ^-1, however the calculated kinetic energy and cumulative drop volume distribution values indicate that the rainfall produced by the 24 and 50WSQ nozzles was equivalent to long periods (>20 min) of natural rainfall at the intensities of 20 and 75 mm h^-1, respectively. The rainfall simulator is easily transported, set up, and operated within a field environment by two individuals and is an effective tool for examining plant pathogen wet deposition processes.