Oak Leaf Blister
Oak leaf blister is a fungal disease which can affect many varieties of oak, but is rarely harmful to the tree. The affected leaves develop blister-like bumps on the leaf surface where the fungus enters the leaf tissue. The tissue around the blisters eventually dies and turns brown. The fungus produces spores in the fall which overwinter in bud scales. The fungus will have the best opportunity for regeneration when the following spring is cool and humid.
To break the annual leaf blister cycle, infected trees should be treated with an appropriate fungicide in the spring, just before bud break. The tree should be thoroughly saturated, which may require specialized high-pressure spray equipment for larger trees.