Leaf-to-leaf~spore dispersal of rust induced by rainsplash*

Rainsplash is an important dispersal mechanism for plant pathogens, but the underlying fluid dynamics are poorly understood. We studied how spore-laden satellite droplets, ejected from rainsplash on a diseased leaf, can subsequently stick to healthy leaves. This natural process was mimicked by rebounding microscopic droplets from an angled superhydrophobic substrate onto an adjacent wheat leaf that was horizontally oriented. The droplets either skipped along the wheat leaf or became stuck, depending upon the droplet's inertia, the orientation of the anisotropic leaf structure with respect to the droplet's path of motion, and whether the leaf was untreated or sprayed with a fungicide. A model successfully demarcated skipping versus sticking behavior by comparing the droplet's inertia against the surface energy required for dewetting to occur upon impact.