Comments: The major threat to Juglans cinerea throughout its entire range is susceptibility to the butternut canker disease caused by the fungus Sirococcus clavigignenti-juglandacearum. The fungus disrupts nutrient flow through cambium areas, which is generally fatal. It may take trees more than 40 years to die, but in many cases, death has rapidly followed infection. Following dieback, this species does not leave live rootsprouts and usually does not leave viable seed. The wood, which is highly prized for cabinet-making and other types of woodworking, is in great demand. "Pre-emptive salvage" cutting, in which any remaining healthy trees are cut in the attempt to get full value for them before they become diseased, is common (at least in the Great Lakes states). The salvage of non-infected trees, however reduces the pool of potentially disease resistant individuals. Woodlot management is also a a form of threat to this species, since it may not involve providing the types of disturbance (e.g., soil disturbance) needed by this shade-intolerant species to successfully reproduce and establish new individuals. Unless management practices are altered to allow for open, disturbed areas, it is unlikely that there will be significant butternut reproduction (Skilling 1993).
In many areas healthy butternut trees have been found growing adjacent to diseased trees and these presumably resistant trees have remained healthy over a 12 year period (Ostr and Woeste 2004).
Butternut canker disease can be identified by the following characteristics or conditions: (1) trees with dying branches or dead tops, and tufts of shoots (epicormic shoots) below the dead portions; (2) discolored bark that in spring exudes an inky-black, thin fluid from cracks in the cankers, and in summer has sooty bark patches that commonly have a white margin; and (3) cankers of various types. In early stages, cankers are sunken and elongate, originating at leaf scars, buds, and in various tree wounds. In latter stages, cankers are visible on older stem and branch portions, many loosely covered with shredded bark and bordered by successive callus layers. Infected trees are also characterized by dark brown to blackish wood portions in elliptical patterns beneath the bark. Dieback occurs through single or coalescing cankers girdling branches, and branch suckers and stem sprouts quickly become infected and die.
An additional threat is hybridization with Juglans ailantifolia (heartnut), a species from Japan which is marketed as a nut tree (McDaniel 1979).
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