The fungus Fomitiporia punctata is primarily a saprophyte of snags and large pieces of deadfall. However, surveys conduced in 2 sites in Quebec (Canada) showed that it also causes a canker rot on living red oak (Quercus rubra L.) and red ash (Fraxinus pennsylvanica Marsh.), with necrosis of the cambium beginning around a rotten knot on the trunk. In total, 52.6% of red oaks at the Beauceville site were infected, and 11.6% of red ashes at the Duberger site, with the incidence of the disease being higher on codominant trees. The median height of cankers did not differ between species, and the average length of the canker was not an indication of the extent of the decay. However, trees with canker less than 75 cm in length and that covered less than 50% of the circumference of the trunk were free of heart rot. There was no relationship between canker size and tree diameter. Large fusiform cankers covering between 0.35 m2 to 0.61 m2 were the result of longstanding infections, and indicative of advanced heart rot and sapwood decay. The potential impact of the disease is especially of concern in riparian ash trees, theatened by emerald ash borer.