The dark discoloration is the Ceratocystis sp. Mortality of bitternut and shagbark hickory has been observed in Wisconsin since the late 1980's. This is similar to occurrences in the 1960's. The fungus can be isolated from sunken bark cankers and discolored wood associated with beetle attacks. In field and greenhouse studies done at the University of Wisconsin, the fungus was found to be highly virulent to bitternut and shagbark hickory, pecan, butternut and black walnut.
Recent reports indicate hickory mortality is apparently widespread across the eastern United States.
It has not been determined if this mortality is always associated with the hickory bark beetle or with the Ceratocystis sp. You can help us delineate the extent of the problem by reporting any hickory mortality. Fungal development deep into the wood on a cross-section of shagbark hickory about one year after bark beetle attack.