White Trunk Rot of Birch
From Bugwoodwiki
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USDA Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State Priv. For., For. Insect and Disease Management., Broomall, PA. p. 123, illus.
Inonotus obliquus (formerly Poria obliqua) causes a trunk rot of both yellow and paper birch. The fungus enters the tree through wounds, especially poorly healed branch stubs. Once the fungus is in the tree, decay is rapid and extensive. A tree with the typical "cinder conk" (a mass of black tissue that forms in openings on the trunk) is usually 50 to 100 percent cull. Other apparently healthy trees in the same stand may also be badly decayed. Viewed at the end of a cut log, decayed wood is yellow with a dark brown border.
The "cinder conk" is not a fruiting body, but a wedge. The structure forces the bark apart, keeping the wound open and allowing the fungus to enter uninfected wood. Every time the tree walls off the fungus, the wedge kills additional tissue; the fungus continues to infects, and a canker forms. Perhaps 6 years after a tree has died and decay has spread throughout the wood to the bark, the fungus fruits. The inconspicuous and short-lived fruiting bodies form under the bark and break through. They are flat, thin, and brown in color.
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 Photo by Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org |  Photo by Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org |
