Regulating the Entire Journey of Pesticide Application on Surfaces of Hydrophobic Leaves Modified by Pathogens at Different Growth Stages.

Under the background of the strategy of reducing pesticide application and increasing efficiency, the mechanism and common technology of efficient and accurate target deposition of chemical pesticides are the key development direction. The interaction between pesticide droplets and a leaf surface affects the deposition behavior of pesticides. However, cucumber leaf surface modified by powdery mildew pathogens at different growth stages is more hydrophobic than a normal leaf surface, which hinders the accurate deposition of pesticides on cucumber powdery mildew leaves. Here, an effective strategy for controlling pesticide efficiency for the entire journey of pesticide application is proposed. Based on the impact dynamics of droplets, the dynamic direction of droplet bounce is determined, the trajectory of droplet rebound is preliminarily determined, and the pinning sites formed by droplets on the surface of cucumber leaves with powdery mildew are confirmed. By analyzing the dynamics in the retraction stage and the energy dissipation rate for droplets after impact, the basic parameters that can be used to simply characterize droplet rebound are screened out, and the effect of addition of an effective surfactant is determined by characterizing the basic parameters (energy dissipation rate, retraction rate, recovery coefficient). The molecular structure formed by the addition of nonionic surfactant in pesticide solution is more appropriate to the interaction between the powdery mildew layer and the pesticide solution, which ensured that the droplets are well wet and deposited on cucumber powdery mildew leaves. Meanwhile, a force balance model for the pesticide droplet wetting state is established to calculate the pinning force for the droplet and predict the transition direction for the droplet wetting state. Impact dynamics combined with force balance model analysis provides a constructive method to improve pesticide utilization during the entire journey for pesticide application on hydrophobic plant surfaces.

Fungal artillery of zombie flies: infectious spore dispersal using a soft water cannon.

Dead sporulating female fly cadavers infected by the house fly-pathogenic fungus Entomophthora muscae are attractive to healthy male flies, which by their physical inspection may mechanically trigger spore release and by their movement create whirlwind airflows that covers them in infectious conidia. The fungal artillery of E. muscae protrudes outward from the fly cadaver, and consists of a plethora of micrometric stalks that each uses a liquid-based turgor pressure build-up to eject a jet of protoplasm and the initially attached spore. The biophysical processes that regulate the release and range of spores, however, are unknown. To study the physics of ejection, we design a biomimetic 'soft cannon' that consists of a millimetric elastomeric barrel filled with fluid and plugged with a projectile. We precisely control the maximum pressure leading up to the ejection, and study the cannon efficiency as a function of its geometry and wall elasticity. In particular, we predict that ejection velocity decreases with spore size. The calculated flight trajectories under aerodynamic drag predict that the minimum spore size required to traverse a quiescent layer of a few millimetres around the fly cadaver is approximately 10 µm. This corroborates with the natural size of E. muscae conidia (approx. 27 µm) being large enough to traverse the boundary layer but small enough (less than 40 µm) to be lifted by air currents. Based on this understanding, we show how the fungal spores are able to reach a new host.