Spatial and temporal enlargement of trunk cankers of Phytophthora cinnamomi in red oak

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Phytophthora cinnamomi Rands is the agent of ink disease on northern red oak (Quercus rubra L.). Cortical cankers on the trunk are the visible symptoms. The fungus causes necrosis of the cambium and phloem, and the tree reacts by forming xylem callus curls. These features can be dated aposteriori on cross sections. The aim of this study was to describe the spatial and temporal development of cankers on cross-sectioned infected oaks. For each lesion, dates of cambium necrosis and formation of callus were recorded at different heights. The following parameters were measured for each lesion: age, height, rate of development, and length and duration of necrosis and canker. Two hundred sixty-three lesions, on 14 trees, were studied. Trees did not exhibit cankers before 9 years of age. All visible trunk cankers could be related to a collar lesion. Phytophthora cinnamomi spreads upwards and can persist for several years, being active seasonally. In this study cambium necrosis occurred preferentially during the first flush. Twenty-nine percent of the lesions were healed over at the collar after 1 year. The collar was less susceptible than the trunk. The other lesions spread rapidly in the cambium of the trunk, which was very vulnerable. They then progressively healed. Therefore, the canker progress curve was bell shaped.

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