Joe also reported that early oak leaf blister symptoms are becoming evident in southwest Ohio on the namesake host of this fungal disease. The leaf disease is caused by the fungus, Taphrina caerulescens. Readers may recognize that this is the same genus as the fungus (T. deformans) that causes peach leaf curl.
The oak leaf blister fungus overwinters in infested buds and twigs. Leaf infections occur during moist periods in the spring as leaves emerge. Early symptoms appear as raised, blister-like, light-green to yellowish-green spots on the upper leaf surface matched with deep depressions on the lower leaf surface. Eventually, the leaf "blisters" become very apparent as they turn dark brown to brownish-black. The blisters can be evenly distributed across the leaf and are distinct from the more angular, vein-based symptoms produced by oak anthracnose.
Although the obvious blisters may reduce the aesthetic appeal of heavily infected trees, the disease typically causes little harm to the overall health of the trees. Even leaves with a relatively large number of infections will retain a significant percentage of functional tissue for photosynthesis. Thus, control measures are generally not required.