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Predicting epidemics: Risk assessment and role of host susceptibility in cucurbit downy mildew outbreaks
P. OJIAMBO (1). (1) North Carolina State University, Raleigh, NC, U.S.A.

Cucurbit downy mildew, caused by the oomycete <i>Pseudoperonospora cubensis</i>, has resurged in the US resulting in a significant impact on cucurbit production and management of the disease at different spatial scales. Understanding the spread of cucurbit downy mildew epidemics at a local and regional scale is fundamental in the management of the disease at multiple scales. In the US, the seasonal spread of the disease that is characterized by typical extinction-colonization makes it possible to quantify the dynamics and risk of disease outbreaks in northern latitudes based on epidemic conditions and inoculum dispersal from the overwintering habitat in the south. Risks of disease outbreaks in the continental US are quantified using Bayesian hierarchical spatial models and risk of disease outbreak is estimated to be high in the mid-Atlantic region. Disease dynamics indicate that the rate of spread of the epidemic wave front in spring-planted annual crop is limited by the seasonal advance of host planting and the epidemic wave is estimated to advance northward at a rate of 12 km/day. Weather factors that influence the risk of disease outbreak at a local scale have been quantified and used to estimate the potential risk of infection based on forecasted temperature and leaf wetness. Host susceptibility can influence risk of disease outbreak at different scales but estimated risk based on most susceptible hosts are probably more practical decision support tool for growers.

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