Butternut Canker
Ophiognomonia clavigignenti-juglandacearum
A lethal, introduced fungal disease that has devastated butternut (white walnut) across its range. It kills trees from the bark inward, forming sunken, oozing cankers that multiply and girdle branches and trunk, and there is little natural resistance.
🔎 How to spot it
Look for elongated, sunken cankers on branches, the stem, and the trunk, often with a black, inky center and a whitish margin, plus sooty-black staining of the bark. Cankers may ooze a dark fluid, especially in spring, and as they expand and merge they girdle limbs, causing branch dieback in the upper crown first. A newly infected tree can look healthy until the inner bark is killed.
🥀 Damage it causes
Individual cankers enlarge, run together, and girdle branches and finally the trunk, cutting off the flow of water and nutrients and killing the tree. The disease is usually fatal, and because butternut has very little resistance it has wiped out the species across much of its native range.
🔬 What causes it
The fungus Ophiognomonia clavigignenti-juglandacearum, an introduced pathogen of unknown origin first found in the U.S. in 1967. Spores spread by rain splash and wind in wet weather, and possibly by insects, infecting through buds, leaf scars, and bark wounds. Repeated infections build many cankers on a single tree.
🛡️ Prevent it
There is no cure, so protect healthy trees by avoiding wounding, and remove and destroy heavily cankered trees that serve as spore sources. Where butternut is replanted, favor the rare trees that show tolerance and any disease-resistant hybrids, and keep trees vigorous and uncrowded.
🧯 If it is already here
No fungicide controls butternut canker in the landscape. Management is sanitation and selection: on minor infections prune cankered branches six to eight inches below the canker, disinfecting tools between cuts, remove severely infected trees, and conserve and propagate the occasional surviving, canker-free tree, since natural tolerance is the best long-term hope.
💡 Good to know
A tree is generally worth saving only if cankers are few and confined to branches; once the trunk is girdled the outcome is fatal. Surviving healthy butternuts in heavily diseased stands are valuable and worth protecting as a source of resistance.
For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.