Oak Leaf Blister (Oak Leaf Curl) This is a fungal leaf disease caused by the fungus Taphrina caerulescens. During cool wet springs, almost every variety of Oak is susceptible. During mid-spring, microscopic spores are produced in leaf spots. These spores are carried by wind and splashing raindrops onto bud scales and twigs where they remain in a dormant stage until the following early spring. At this time, rain washes the spores onto young leaves where infection takes place. Depending on weather conditions, small circular spots begin to develop in 2 to 4 weeks. Spores produced on these spots will lodge in bud scales and again remain resting until the following spring. Cool wet weather is required for germination on young leaves, and if these conditions continue, severe infection can occur.
Though aesthetically unpleasing, this fungus does not pose enough of a problem to require a fungicide treatment. If a well established tree has a premature leaf drop in early to mid summer, it will usually flush back out before fall. If a tree defoliates in late summer or fall, it will have little to