Movement of plant pathogens in the crop canopy

Many spores released by plant pathogens are deposited within a few metres of their source. The distribution pattern within this zone influences the rate of spread of disease, and also controls the number of spores that leave the canopy and contribute to long-range dispersal. It would thus be valuable to develop a theory to describe the movement of spores within crop canopies, and explain the effects of airflow, crop structure, and height and mode of spore release. Conventional diffusion theory gives serious errors when used within a crop, and a random-walk theory, in which individual particle trajectories are simulated, provides a promising alternative. The three components of velocity are generated as Markov sequences with mean statistics that relate to the Eulerian windfield, and with correct Lagrangian timescales. This theory can readily incorporate the release of spores in gusts, and some implications for spore distribution are explored.

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