Butternut Canker

Butternut canker is a lethal fungal infection of butternut trees (Juglans cinerea).
Photographer: Mike Ostry, US Forest Service.
Butternut canker (Sirococcus clavigignenti-juglandacearum) is currently eliminating entire populations of butternut trees (Juglans cinerea, also called white walnut) throughout its range in the United States.

The origin of the fungus is unknown, but it was probably introduced from outside the United States in the mid 1900s.1

Infected trees typically have dead branches or a dying top. Cracked, sunken, discolored bark may ooze black inky fluid in spring, or appear sooty with whitish margins in summer. Where the bark has come loose, dark oval stains may be visible on the wood beneath.2 Controls currently do not exist.3

Rain splash and wind (and possibly insects and other animals) spread the spores to other butternut trees and to black walnut (Juglans nigra). However, black walnut, which is related to butternut and overlaps part of its geographic range, appears to be resistant to the fungus.

Butternut has prized edible nuts. Never a very common tree, butternut is becoming hard to find. Since some trees in the U.S. seem to display resistance, there is hope that the species can outlive the disease.