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Schmalz, Timothy F.

Forestry Program

2006

M.S.

Butternut canker, caused by the fungus Sirococcus clavigignenti-juglandacearum (Nair, Kostichka & Kuntz) (Scj), is responsible for extensive decline and mortality throughout the native range of butternut (Juglans cinerea L.). A study conducted from 1993 to 1996 in northern Vermont indicated butternut mortality and Scj infection rates of 12% and 92%, respectively, and positive associations among Scj presence, reduced crown vigor, and increases in secondary pathogens, including Armillaria sp. and other root rotting fungi. Analysis of data collected during the 2001 and 2002 summer field seasons indicated a continuing Scj-related decline in butternut health. Tree mortality increased to 41%, and Scj infection rates on remaining surviving trees increased from 88 to 96%. Also, general health indicators decreased significantly, and the incidence of secondary pathogens increased significantly during the interim. Butternut canker played a significant role in mortality increases, root rot occurrences, and crown ratio decreases. Trees that exhibited main stem or root cankering in 1996 were also more likely to be dead or exhibit Armillaria, other root rots, and/or heart rot infections, and more epicormic branching in 2002 compared to uninfected trees. Cankering and mortality occurred at similar rates across all crown classes, stocking levels, and diameter classes. Suppressed trees were most likely to die or exhibit slowest radial growth rate between 1996 and 2002, but dominant trees exhibited the highest rates of Armillaria root rot, other root rots, and heart/think rots. When buttemut canker was present, heart/trunk rots were significantly more common in under and adequately stocked stands than in overstocked stands, and epicormic branching rates were significantly higher in understocked stands. Mean diameter and incremental diameter increases were significantly lower in cankered trees than in healthy trees. Logistic regression models found tree mortality was significantly associated with canker presence, root rots, crown class, and stocking level. These data indicate that Scj is contributing to decline, increased susceptibility to secondary pathogens, and accelerated mortality of butternut in Vermont.