National 4-H Forestry Invitational Training Reference
in Cooperation with the US Forest Service
Forest Health Protection Unit, Northeastern Region
WHITE TRUNK ROT of BIRCH,
Inonotus obliquus
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 infect, 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.
(a & b) The "cinder conk", the blackish-red tissue mass that forms on the trunk, is a not the fungus's fruiting body, but a wedge that separates the wood fiber inside the trunk allowing the fungus to enter uninfected wood. Eventually a canker forms on the trunk (right) as additional wood tissue is repeatedly killed.
