| Description |
Turbulent dispersion is one of the most important transport mechanisms in the life cycle of many fungal plant pathogens. Without turbulent dispersion, inoculum spread would be confined to adjacent leaves, limiting the severity of epidemics. Thus, understanding the mechanisms that influence and control dispersion from disease foci are of primary importance towards improving our ability to prevent and respond to disease outbreaks. In sparse canopy environments, the influence of canopy geometry (row spacing, canopy height, and plant density) on turbulent fluxes can be problematic for traditional dispersion modeling techniques that rely on assumptions of steady or horizontally homogeneous velocity fields. Here, the link between canopy geometry, turbulent fluxes and particle dispersion gradients in sparse agricultural canopies was explored using a Lagrangian particle dispersion model linked to velocity fields from large-eddy simulations. In particular, particle dispersion from line sources in plant canopies with geometry characteristic of grape vineyards were examined. Simulations were performed with varying row spacing and plant density to characterize particle dispersion within the canopy over a large range of length scales. It was of primary importance to examine how changing plant geometry could limit the spread of pathogens over large length scales, thus limiting the speed at which epidemics spread. Unresolved particle motion was modeled by solving a form of the Langevin equation and particle deposition onto vegetation is modeled using a stochastic technique. Results show that as overall canopy density decreases, bulk velocity in the canopy increases exponentially. This has a substantial impact on particle concentrations downstream of the source, as mean particle velocity influences concentrations. Furthermore, as canopy density decreases, particles tend to travel further before being deposited. However, as canopy density decreases, fewer particles tend to escape the canopy, which corresponds to a lower probability of long-distance transport. Thus, in less dense geometries, particles tend to spread further in near-source areas inside the canopy, but transport is more likely to be confined to smaller length scales. More dense canopies tend to limit transport near the source due to increased drag and deposition, but increased canopy escape increases the probability of transport over large length scales. |
