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Modeling Disease Progression of Camellia Twig Blight Using a Recurrent Event Model

To improve control of camellia twig blight (CTB) using sanitation methods, a more complete epidemiologic understanding of this disease is necessary. Three CTB disease stages were modeled using recurrent event analysis. Wound inoculated stems were observed at regular intervals for appearance of disease symptoms. Survival times (time from inoculation until symptom appearance) for the three disease stages (mild, moderate, and severe) were regressed against stem diameter, monthly mean hours/day within a specified temperature range (15 to 30°C), and season (spring, summer, fall, and winter). For all three CTB disease stages, stem diameter had a protective effect on survival times, while monthly mean hours/day in the specified temperature range and warmer seasons were risk factors. Based upon median ratios, the mild disease stage developed 2 to 3 times faster in spring, summer, and fall than in winter. Similarly, moderate and severe disease stages developed 2 to 2.5 times faster. For all three disease stages, seasonal differences in stage development were smaller among fall, spring, and summer, varying from 1 to 1.6 times faster. Recurrent event modeling of CTB progression provides knowledge concerning developmental expression of this disease, information necessary for creating a comprehensive, integrated disease management program.