Problem: Oak Leaf Blister
Leaf blister is caused by a fungus (Taphrina caerulescens) that is unsightly but rarely harms the tree. It is a problem on various species of oak, particularly red, black, scarlet, and live oaks. The fungus spends the winter in bud scales on the tree. During cool, wet spring weather, it enters the leaves as they develop. Green blisters form where the fungus has entered and the infected tissue eventually turns brown and dies. In the fall, the fungus produces overwintering spores. If the following spring is cool and wet, the cycle begins again.
If leaf blister was a problem the previous year and the weather the current spring is cool and wet, apply a fungicide labeled for this disease, following label directions.