Relationship between pathogen splash dispersal gradient and Weber number of impacting drops.

We examined the potential of the dimensionless Weber number of an impacting water drop for predicting the associated gradient of pathogen dispersal. Previously shown to be related to the mechanisms of splash droplet formation, the Weber number compares the inertial forces to surface tension force of the drop. Based on new data on tomato late blight and previously published data on wheat rust diseases and on strawberry diseases, the number of spores splashed by incident drops at a given distance from the source is expressed as a negative exponential function of distance multiplied by the pathogen deposition term in the immediate vicinity of the source. Results show strong evidence that the pathogen deposition term is well described by a power law function of the Weber number