Factors Influencing the Regional Dynamics of Butternut Canker.

Butternut (Juglans cinerea) is an important component of native biodiversity in eastern North America. Of urgent concern is the survival of butternut, whose populations are declining rapidly, in large part due to an exotic pathogen, Ophiognomonia clavigignenti-juglandacearum, that causes butternut canker. The disease presently occurs throughout the range of butternut in North America, causing branch and stem cankers, dieback, and tree mortality. Despite the existential threat posed by O. clavigignenti-juglandacearum to butternut, a detailed understanding of the factors that drive cross-scale disease patterns is lacking. Therefore, we investigated the association of a range of factors, including tree attributes, topography, and weather, with butternut canker spatial dynamics at different scales using data collected in the province of Quebec, Canada. Trunk canker damage and dieback showed distinct geographic patterns. Bark phenotype was not significantly associated with trunk canker damage. Results suggest that open or dominant trees may show less dieback than intermediate or suppressed trees. Probability of the presence of trunk canker and percent dieback were proportional to the tree diameter at breast height. Temperature was positively associated with disease severity at a 1-km scale. Our results provide strong evidence that multiple factors, notably weather, influence butternut canker epidemiology.