Butternut canker

Ophiognomonia clavigignenti-juglandacearum
Butternut canker on a stem
Scientific classification
Kingdom:	Fungi
Division:	Ascomycota
Class:	Sordariomycetes
Order:	Diaporthales
Family:	Incertae sedis
Genus:	Sirococcus
Binomial name
Sirococcus clavigignenti-juglandacearum

Sirococcus clavigignenti-juglandacearum is a mitosporic fungus that causes a lethal canker disease of Butternut trees (Juglans cinerea). Known in the vernacular as Butternut Canker, it is also known to parasitize other members of the Juglans genus on occasion, and very rarely other related trees including hickories. The fungus is found throughout North America, occurring on up to 91% of butternut trees, and may be threatening the viability of butternut as a species.

Butternut, the primary host of S. clavigignenti-juglandacearum, is found in mixed hardwood forests throughout central North America, from New Brunswick to North Carolina.

Butternut canker was identified as an invasive species in 1967. It was first discovered in Wisconsin, but has since spread to other states and into Canada. Its native origin is unknown, but possibly in Asia given the resistance of Asian walnuts to the disease. The United States Forest Service found that 84% of all butternuts in Michigan as well as 58% of all trees from Wisconsin have been affected; later surveys by the Wisconsin Department of Natural Resources revealed that 91% of all living trees in Wisconsin were diseased or cankered. In Virginia and North Carolina, the butternut population has been reduced from 7.5 million to 2.5 million.

Broad dead areas known as cankers form on the main stem, branches, young twigs, and exposed roots. Most cankers are covered with bark cracks. The fungus forms a dark mat of branching mycelium below the bark, from which arise peg-like hypha that lift and rupture the bark. In the later stages of infection, the bark above the canker is shredded.

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Wikipedia