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Butternut Canker

Robert L. Anderson
Forest Pathologist
USDA Forest Service
Southern Region - Forest Health
Asheville, NC 28802


-Butternut canker, caused by the fungus Sirococcus clavigignenti-juglandacearum, is killing butternut (Juglans cinerea) throughout its range in North America. First report from Wisconsin in 1967, the disease has killed up to 80 percent of the butternut in some states. The primary hope for biological control rests with genetic selections. Healthy trees, and infected trees that apparently have resistance and survived the disease, have been found in severely affected forest stands in 19 states. Clonal and seedling propagation of trees exhibiting resistance is being used to evaluate breeding and future restoration efforts. Hybrids are also being evaluated as an alternative biological control technique. A number of trees have been observed recovering from butternut canker. This pattern or major loss of tree followed by recovery of the remaining trees is typical of hypovirulent fungal strains and needs exploration.

Butternut (also called White Walnut and oilnut) is a small to medium size tree that matures around 75 years of age, is shade intolerant and reproduces by sprouting or seed germination. It grows on rich loamy soils, as well as, drier rocky soils. Butternut typically is mixed with other hardwoods such as black walnut. The species is found in New England, south to Northern Georgia, in the United States from west to central Missouri and north to the Lake State (Distribution Map). It hybridizes with other species of Juglans such as heartnut, Japanese walnut, English Walnut, little walnut, and manchurian walnut.

Butternut is valued for its wood for furniture, paneling, specialty products, carving, and nut production. It is second in value only to black walnut. Although walnut is not commonly found growing together in great numbers, there is concern to maintain a viable butternut population to preserve biodiversity.

The Disease

Butternut is being killed throughout its range in North America by a fungus (Sirococcus clavigignenti-juglandacearam). Butternut canker has been found in 55 counties in the Southern United States (Occurrence Map). Butternut trees have dramatically been reduced and it has been listed under Category 2 on the list of Endangered and Threatened Plants under the Endangered Species Act. This category implies that there is some evidence of vulnerability, but not enough data to support listing at this time.

The canker was first reported on butternut in southwestern Wisconsin in 1967. Detailed examination of cankers indicates that butternut canker has been present in the United States since the early 1960's but it was not until 1979 that the true cause of butternut canker was identified. Its origin is unknown but the evidence points to this being a recent introduction. The rapid spread of the fungus throughout the butternut range, highly aggressive nature of the disease on infected trees, scarcity of resistant trees, the lack of genetic diversity in the fungus, and age of the oldest cankers (50 years) all support the theory of a recent introduction.


The fungus causes multiple cankers on the main stem and branches. Young cankers are elongated, sunken areas commonly originating at leaf scars and buds, often with a inky black center and whitish margin. Peeling the bark away reveals the brown to black elliptical areas of killed cambium. Older branch and stem cankers are perennial, found in bark fissures or covered by shredded bark, and boardered by successive callus layers. Cankers commonly occur at the base of trees and on exposed roots. Branch cankers usually occur first in the lower crown and stem cankers develop later from spores washing down from branch cankers. The fungus can survive and sporulate on dead trees for at least 20 months.

Spores of the fungus are disseminated from fruiting bodies by rain splash and possibly by insects. Spores are produced throughout the growing season, and once airborne can survive and be dispersed long distances during favorable weather conditions of cool temperatures and overcast skies.


Butternut canker kills trees of all ages. Branches and young saplings may be killed by a single canker, however, older trees are killed by multiple, coalescing cankers that either progressively kill the crown or eventually girdle the stem. Sprouts, if they develop, also become infected and are killed usually within the first few years. The nut husk can also become infected.

USDA Forest Service Inventory and Analysis forest inventory data show a dramatic decrease in the number of live butternut trees in the United States. Live butternut decreased by 58 percent in Wisconsin and 84 percent in Michigan in the last 15 years. A recent Wisconsin Department of Natural Resources survey revealed that 91 percent of the live butternut throughout Wisconsin were diseased. Surveys in the southeast United States revealed that 77 percent of the butternut have been killed in North Carolina and Virginia, and infected trees continue to be found in new counties in most of the United States.

Biological Control Potentials

There is no known control for butternut canker. Fungicides have been tested with some success but are not ready for field use. Agents which would be antagonistic to the fungus such as hypo virulent fungal strains have not been detected. However, a number of trees have been observed recovering from butternut canker. This pattern or major loss of tree followed by recovery of the remaining trees is typical of hypovirulent fungal strains and needs exploration.

The fungus is not known to occur in other counties, so the potential for finding a biological control from another geographic area is limited The primary potential for biological control of the butternut canker is through genetics.

Disease free trees are rare but have been found in 19 states. These trees are growing along side of severely cankered trees. The rapid spread of the fungus also indicates that these trees have received prolonged exposure to the fungus. Each tree is tagged and placed into a superior tree selection program. Scion wood is collected from each of the disease free trees in February to March. The scion wood is grafted on root stock at the University of Tennessee and at the North Central Forest Experiment Station in St. Paul, Minnesota. Nuts are also collected and grown in a nursery when available.

These tree selections, grafted and seedling are placed into progeny tests and evaluated for growth traits, screening tests for relative resistance and placed in seed orchards for future use. It is too early to evaluate the success of selecting for disease resistance but the preliminary data is promising.

Butternut also hybridges with trees such as heartnut. Some of these hybrids have been located in the field and are being evaluated. These trees provide the potential for using back crosses to produce progeny which contain a small amount of heartnut but are resistant.

Retaining Trees for Genetic Selections

In the late 1980's the need for identification and conservation of butternut for tree selection and breeding was recognized. The following guidelines have been prepared:

Literature Sources

Clark, F. 1965. Juglans cinerea L. Butternut. In Fowells, H.A. [ed.] Silvics of Forest Trees of the United States. USDA For. Serv., Agric. Handb. 271, p. 208-210.

Fleguel, V. Rosemary. 1996. A Literature Review of Butternut and the Butternut Canker Ontario Ministry of Natural Resources, Eastern Ontario Model Forest, Information Report No. 20. 32 pp.

Kuntz, J.E., A.Prey, and V. Nair. 1979. The etiology, distribution, epidemiology, histology, and impact of butternut canker in Wisconsin. In Proceeding of the Symposium on Walnut Insects and Diseases. Gen. Tech. Rept. NC-52. USDA For. Serv., North Cent. For. Exp. Stn., p. 69-72.

Nair, V.M.G., C.J. Kostichka, and J.E. Kuntz. 1979. Sirococcus clavigignenti-juglandaceearum: An undescribed species causing canker on butternut. Mycologia 71:641-646.

Nicholls, T.H. 1979. Butternut canker. In Proceedings of the Symposium on Walnut Insects and Diseases, Gen. Tech. Rept. NC-52. USDA For. Serv., North Cent. For. Exp. Stn., p. 73-82.

Orchard, L.P. 1984. Butternut canker: host range, disease resistance, seedling-disease reactions, and seed-borne transmission. PhD. Thesis. Univ. WI, Madison. 145 pp.

Orchard, L.P., R.P. Guries, and J.E. Kuntz. 1981. Butternut canker: Screening seedlings for disease resistance (Abstr.) Phytopathology 71:247.

Ostry, M.E., M.E. Mielke, and R.L. Anderson. 1996. How to identify butternut canker and preserve butternut. St. Paul, MN. U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station.

Ostry, M., M. Mielke, and D. Skilling. 1994. Butternut - Strategies for managing a threatened tree. Gen. Tech. Rept. NC-165. USDA For. Serv., North Cent. For. Exp. Stn. 7p.

Tisserat, N. and J.E. Kuntz. 1982. Epidemiology of butternut canker. In Proceedings of the Symposium on Black Walnut For the Future. Gen. Tech. Rept. NC-74. USDA For. Serv., North Cent. For. Exp. Stn., p. 18-22.

Tisserat, N. and J.E. Kuntz. 1983b. The etiology and epidemiology of butternut canker. In Ann. Rept. NNGA No. 74, p. 30-36.

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