The influence of leaf surface roughness on the spreading of oil spray drops

Abstract
SUMMARY: The effect of surface roughness of leaves on the retention and spreading of oil drops is considered. Three types of roughness have been recognized. Leaf hairs and protruding or recessed veins underlying the cuticle constitute a macroscopic roughness. Microscopic roughness is determined by epidermal cell size and arrangement, which influence the geometry of the grooves between these cells. Ultra‐microscopic roughness is determined by the size, shape and organization of the epicuticular wax system. The effect of environmental conditions on surface roughness is also considered and the significance of the spreading of spray drops is discussed in relation to the application of pesticides.