Butternut canker is caused by a fungus (Sirococcus clavigignenti-juglandacearum) that infects butternut (Juglans cinerea) through openings such as buds, leaf scars, and insect wounds. Spores of the fungus enter the tree and create cankers that are elongated, sunken, often with an inky black center and whitish margin. When large cankers form (or many smaller cankers coalesce), twigs and branches become girdled, resulting in dieback. Trunk and buttress roots can also become girdled, ultimately killing the tree. The spores can be carried on the nuts and infect the tree upon germination. The fungus is spread by rain-splashed spores, wind, and insects. Spores can remain viable on dead trees for at least two years. Armillaria root rot is often associated with trees infected with butternut canker and may hasten mortality.

Signs and symptoms

• Dead or dying branches at the tops of butternut trees

• Cankers in the bark will ooze black fluid in the spring and have a dark center and whitish margin in the summer.

• Young cankers often appear around leaf scars, buds, or wounds and may be elongated and sunken into the bark.

• Old cankers may have layers of overgrown trunk tissue and loose bark covering them.

• Stained wood beneath the bark that is dark brown to black and oval shaped.

See image slideshow above for signs and symptoms.