Butternut canker

Butternut canker is a fungal disease of butternut trees. We do not know whether this fungus is native or introduced or how long it has been in North America. Although first detected in Wisconsin in 1967, it was probably present much earlier.

Butternut trees are infected through buds, leaf scars, and possibly through insect wounds or other openings in the bark. When a tree is infected with this disease, patches of bark are killed. These dead areas, called cankers, can eventually encircle branches and stems and cut off the flow of water and food within the tree. This is called girdling. Reproductive structures of the fungus form in the cankers and are spread down the tree by rain water. As the number of infected sites on the tree increases, dieback in the crown accelerates. Heavily infected trees are killed.

Butternut is a relatively minor component of forests in the eastern United States. The nuts, when present, are an important food source for some types of wildlife, and quality butternut wood currently ranks among the highest in value of all hardwood trees. Butternut also is important as a part of biological diversity in our forest. The map below shows areas of the forest where surveys have confirmed that butternut canker is present:

During the past 10 to 15 years, butternut canker has contributed to a dramatic decrease in the number of live butternut trees found in the United States. The decrease has been as much as 80% in some states. Management strategies for butternut canker in the eastern United States include monitoring efforts to assess the general health of butternut trees, conservation of certain individual butternut trees that may have resistance to this disease, and efforts to breed resistant strains of butternut.