Hypoxylon Canker
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Importance
Hypoxylon tinctor is a fairly common saprophyte of dead sycamores and other hardwood species. The fungus occasionally produces cankers on live sycamores, taking advantage of trees in “decline” or under stress. In Georgia, it has been associated with cankers caused by the canker stain fungus Ceratocystis fimbriata f. platani.
Identifying the Disease
Irregularly defined, somewhat inconspicuous cankers tend to follow the wood grain, occurring mostly on the main stem and larger branches (fig. 31a). Older, decayed cankers may have holes from insect borers or woodpeckers (fig. 31b).
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| Figure 31a. - Hypoxylon canker with bark removed to reveal fungal stromata. |
Identifying the Fungus
The darkbrown to black fungal stromata (1 to 5 cm x 2 to 30 cm) may be evident through sloughing bark or may be partially concealed by bark (fig. 31c). Ascospores are produced in tiny cavities embedded in the hard surface of the stromata.
Biology
The occurrence of H. tinctor seems to be associated with extensive thinning in natural stands, where other fungal pathogens and sun scald may be weakening trees. Infection by windblown or rain-splashed ascospores probably occurs through wounds in the bark.
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| Figure 31b. - Dead, decaying limb showing dark fungal stromata and a woodpecker using the limb as a nesting site. |
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| Figure 31c. - Closeup of H. tinctor fungal stromata. |
Control
H. tinctor apparently is less able to infect healthy, vigorously growing trees. Therefore, maintaining good tree vigor and minimizing bark wounds should prevent cankers caused by this fungus.
References
Leininger, T.D; Solomon, J.D.; Wilson, A. Dan; Schiff, N.M. 1999. A Guide to Major Insects, Diseases, Air Pollution Injury, and Chemical Injury of Sycamore. Gen. Tech. Rep. SRS-28. Asheville, NC: USDA Forest Service, Southern Research Station. 44 p.
