Butternut (=white walnut or oilnut), Juglans cinerea, is a highly valued eastern hardwood species. The wood is prized for veneer, cabinetry, and especially for carving. Butternut also is an important nut species and can produce copious amount of nuts for a variety of wildlife species. The nut is very palatable for human consumption, and there are a number of cultivars that have been selected for nut production (Millikan & Stefan, 1989).
Presently, butternut populations are being killed by an apparently exotic fungal disease that causes multiple branch and trunk cankers. The host tree is killed when multiple trunk cankers join and girdle the tree. Although the disease was first discovered in 1967 in southwestern Wisconsin (Renlund, 1971), coring of infected trees in the southern portion of the butternut’s range suggest that the disease was introduced into the southeast around 70 years ago (Anderson & LaMadeleine, 1978). Over three quarters of the butternut trees in the south are now dead (Burkman et al., 1998). Originally known as Sirococcus clavigignenti-juglandacearum, the latin name of this disease was officially changed in 2011 to Ophiognomonia clavigignenti-juglandacearum.
USFS scientists and managers developed a conservation priority-setting framework for forest tree species at risk from pest & pathogens and other threats. The Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) uses FIA data and expert opinion to group tree species under threat by non-native pests into vulnerability classes and specify appropriate management and conservation strategies. The scientists prioritized 419 tree species native to the North American continent. The analysis identified 15 taxonomic groups requiring the most immediate conservation intervention because of the tree species’ exposure to an extrinsic threat, their sensitivity to the threat, and their ability to adapt to it. Each of these 15 most vulnerable species, and several additional species, should be the focus of both a comprehensive gene conservation program and a genetic resistance screening and development effort.
Butternut is one of six species that face severe pest threats, are highly sensitive to that pest, but have high capacity to adapt (according to CAPTURE project). The project urges immediate conservation and the facilitation of resistance through breeding.
Butternut canker has spread throughout much of the tree’s range, reaching Canada in 1990. Unlike American chestnuts and chinkapins (Castanea spp.), butternut will not sprout from the root crown when the top is killed by cankers. Seedlings, young sprouts, and mature trees are all killed by the disease (Prey & Kuntz, 1982). Therefore, when butternut canker disease destroys a population, that particular gene pool is lost forever, as there is no possibility for natural reproduction. The rapid demise of the species has caused the U. S. Fish and Wildlife Service to declare the butternut “a species of concern.”
Despite the severe mortality from butternut canker disease, there is reasonable hope for returning butternut to eastern landscapes. Two groups of scientists and field experts from various organizations centered at the USDA Forest Service, North Central Experiment Station in Minnesota and at the University of Tennessee, have been working for a number of years on the detection of resistance and genetic resource conservation (Ostry et al., 1994, 1996; Schlarbaum et al., 1997; van Manen et al., 2002). Plantings to conserve the genetic diversity in surviving butternut populations have been established at various locations throughout the eastern states. Trees with putative resistance and immunity have been selected and are presently being evaluated for inclusion in breeding programs.
Anderson, R. L. and L. A. LaMadeleine. 1978. The distribution of butternut decline in the eastern United States. United States Department of Agriculture, Forest Service, NE Area, State and Private Forestry Report S-3-78. 4 pp.
Burkman, W. G., J. S. Vissage, W. H. Hoffard, D. A. Starkey, and W. A. Bechtold. 1998. Summary Report: Forest Health Monitoring in the South, 1993 and 1994. United States Department of Agriculture Forest Service Southern Research Station, Resource Bulletin SRS-32.
Millikan, D. F. and S. J. Stefan. 1989. Current status of the butternut, Juglans cinera L. Ann. Rep. North. Nut Growers Assoc. 80: 52-54.
Ostry, M. E., M. E., Mielke, and D. D. Skilling. 1994. Butternut – strategy for managing a threatened tree. USDA For. Ser. Gen. Tech. Rep. NC 165. 7 pp.
Ostry, M. E., M. E. Mielke, and R. L. Anderson. 1996. How to identify butternut canker and manage butternut trees. USDA For. Ser., North Central Exp. Stn., Northeast. Area State and Private Forestry, and Region 8, State and Private Forestry, HT 70.
Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/
Prey, F. J. and J. E. Kuntz. 1982. The distribution and impact of butternut canker. In Black walnut for the future. USDA For. Serv. Gen. Tech. Rep. NC-74. pp. 23-26.
Renlund, D. W. (ed.). 1971. Forest pest conditions in Wisconsin. Wis. Dept. Nat. Res. Ann. Rep. 53 pages.
Schlarbaum, S. E., F. Hebard, P. C. Spaine and J. C. Kamalay. 1997. Three American tragedies: chestnut blight, butternut canker, and Dutch elm disease. Proc. Exotic Pest of Eastern Forests, April 8-10, 1997, Nashville, TN, pp. 45-54.
van Manen, F. T., J. D. Clark, S. E. Schlarbaum, K. Johnson, and G. Taylor. 2002. A model to predict the occurrence of surviving butternut trees in the southern Appalachian region. In Predicting Species Occurrences: Issues of Scale and Accurancy, J. M. Scott, P. J. Heglund, M. L. Morrison, J. B. Haufler, M. G. Raphael, W. A. Wall, and F. B. Samson, eds. Island Press. Chapter 43, pp. 491-497.