Divergent droplet impact dynamics on morphologically distinct crop leaves with similar wettability

Droplet impact on plant leaves governs pesticide retention and spray efficiency; however, surfaces with similar wettability can exhibit markedly different impact dynamics due to variations in surface morphology. Here, we investigate droplet impact on wheat and canola leaves with similar wettability but distinct morphologies. Wheat leaves exhibit anisotropic hill–valley structures with uniform wax distribution, whereas canola leaves exhibit micro-bump structures with non-uniform wax coverage. Water droplet impact experiments were conducted using high-speed imaging over a Weber number range of 24–140. Both surfaces produce similar drop impact behaviour at low Weber numbers but, despite similar static contact angles with water (~150º), the droplet impact outcomes diverge significantly at higher Weber numbers. The maximum spreading factor follows distinct power-law scaling with Weber number, β max ∝ We 0.47 for wheat and ∝ We 0.40 for canola, exceeding classical inertial–capillary predictions. Classical scaling models developed for smooth surfaces fail to capture the observed spreading behaviour. The normalised contact time decreases significantly with increasing Weber number on wheat leaves, deviating from the inertial–capillary limit, while remaining nearly constant on canola leaves. These differences are attributed to morphology-induced variations in lamella spreading and recoil dynamics, demonstrating that static wettability alone is insufficient for predicting droplet impact dynamics on natural leaf surfaces.