Butternut canker symptoms
Joseph O'Brien, USDA Forest Service, Bugwood.org
Butternut (Juglans cinerea), also known as white walnut, commonly grows on rich loamy soils in mixed hardwood forests. It is being killed throughout its range by Sirococcus clavigignenti-juglandacearum, a fungus most likely introduced from outside of North America.
Keywords: fungus, rainsplashed spores, perennial cankers, annual cankers, pegs, girdling, Juglans cinerea, white walnut
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Butternut canker distribution
The fungus initially infects trees through buds, leaf scars, and possibly insect wounds and other openings in the bark, rapidly killing small branches. Cankers develop throughout a tree, but commonly occur on the main stem, at the base of trees and on exposed roots. Young, annual cankers are elongated, sunken areas usually originating at leaf scars and buds, often with an inky black center and whitish margin. Under the bark, the fungus forms pegs that break through the outer bark surface, exposing the spores. Spores produced on branches are carried down the stem by rain, resulting in multiple perennial stem cankers that eventually girdle and kill infected trees. Older perennial branch and stem cankers are often found in bark fissures, or covered by bark and bordered by successive callus layers. Butternut is the only natural host known to be killed by the fungus. The disease has contributed to as much as an 80 percent decrease in living butternut in some States. The fungus can survive on dead trees for at least 2 years.