To prevent the fungus, the plants would need to be sprayed with a fungicide just prior to buds opening, and perhaps again 10 days later. Oak Leaf Blister. This is another leaf fungus that appears nearly every spring. As the name suggests, oaks are the host for this fungus. Nearly all oak varieties can get oak leaf blister, though some species seem to get it more than others.
Symptoms first appear as round, cupped or distorted areas of the leaves, giving a puckered look.
Later the spots turn brown, and look similar to blisters. If spots are numerous on a leaf, it could fall prematurely in the summer. This fungus overwinters on dormant buds, ready to infect leaves as the buds break dormancy in the spring. When wet, cool conditions occur during bud break, fungal infection can occur. Symptoms usually don't appear until several weeks after initial infection.