Summer 1995
Search Continues for Canker-Resistant Butternut
R. Todd Culp
IDNR Division of Forestry
The butternut, or white walnut (Juglans cinerea) is being killed by a fungus called Sirococcus ctavigignenth juglandacearum. Commonly known as butternut canker disease, the fungus is decimating the population of already scarce butternuts. The Division of Forestry is still engaged in the hunt for healthy butternuts that are near cankered butternuts. Thus far, the search has yielded a few possibilities. The pioneers of the Indiana butternut survey, Phil Marshall and Mark Coggeshall, hope to locate more candidates to ensure success and to maintain genetic diversity within the pool of resistant trees.
The Sirococcus fungus causes cankers to form on the butternut. These cankers can be found on the branches, the trunk, and the buttress roots. In the first stages of infection, the disease can be most easily observed by black sooty patches on the surface of the bark. In the summer, the cankers will exude a black fluid from forming cankers. The fluid will dry during the summer but will leave behind the dark stain on the bark. Eventually, the fungus will cause gaps in the branches and trunk that are often covered by deteriorating bark. These cankers can eventually girdle the tree, causing death. Presently, no silvicultural methods are known to prevent the further spread of the disease. Even infected trees that are felled continue to exhibit Sirococcus sporulation for over a year.
The most promising way of increasing the population of butternuts is to find trees that resist the fungi. Healthy butternut trees that are found near diseased butternut trees may prove to have a natural resistance to the fungus. The effort by the Division of Forestry is concentrating on finding these healthy butternuts that are close to diseased butternuts. After these trees are located, cuttings will be taken around February and grafted onto rootstocks. The trees will then be inoculated with the disease to determine if they are resistant or if they have just not been directly exposed to the fungus. If you know of healthy butternuts that are close to cankered butternuts, please write to: Butternut Survey, c/o Phil Marshall - Forest Health Specialist, VatIonia State Tree Nursery, 2782 West County Road 540 South, Vallonia, Indiana 47281 or call (812) 358-3621 .