Oak Leaf Blister

This disease, caused by the fungus Taphrina caerulescens (a relative of the peach leaf curl fungus) is quite noticeable this late spring and into summer on a range of oak species. The fungus overwinters in infested buds and twigs and causes infection during moist periods in the spring as leaves emerge. On upper leaf surfaces the “blister-like” somewhat raised spots are greenish to yellow-green, eventually turning brown. On lower leaf surfaces these blistered areas appear as depressions in the leaves. Damage is typically not severe and controls (which to be effective would have to be applied in spring as leaves emerge) are generally not recommended. Some leaf drop may occur and releafing is common in such situations.  

Oak Leaf Blister