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Oral: Dispersal at Multiple Scales: A Key to Outbreak of Disease Epidemics


Dispersal of Pseudoperonospora cubensis: Basis for Forecasting Cucurbit Downy Mildew Epidemics
P. OJIAMBO (1) (1) North Carolina State University, U.S.A.

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In the United States, Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, is largely thought to overwinter in subtropical areas in southern Florida where mild winters allow for year-round survival of its host. Thus, epidemics in northern states, annually depend on the dispersal of sporangia from the south during periods of strong southerly winds. To facilitate forecasting of initial outbreaks, the Cucurbit ipmPIPE Forecasting system integrates information on known disease sources, outputs from trajectories of sporangia transport, weather conditions along trajectory pathways and host availability, to predict the risk of disease outbreak. The Lagrangian particle dispersion model FLEXPART is used to calculate long-range and mesoscale dispersion of sporangia from known sources. The FLEXPART has been modified to account for survival of P. cubensis sporangia during aerial transport. This modification has involved inclusion of a multiplier factor described by an exponential decay model relating sporangia survival to cumulative solar radiation dose during dispersal. The source strength input into the FLEXPART model now accounts for disease severity at the source and this has resulted in better estimates of the standing crop of sporangia that can escape and be available for dispersal. Incorporating of information on biology of P. cubensis in the dispersal framework has resulted in realistic forecasts of disease outbreaks in the eastern United States.