A Fuzzy Disease on Oak Tree Leaves

Leaf Blister

• A fungus is responsible for fuzzy disease on oak tree leaves. The condition, which is known as leaf blister, is caused by the Taphrina caerulescens fungus and results fuzzy patches forming on the leaves. These patches are the fungi's fruiting bodies that produce millions of spores capable of floating through the air and infecting adjacent leaves or trees.

Life Cycle

• While all species of oak are vulnerable to leaf blister, red and black oaks are the most susceptible. The fungus overwinters on the leaves or on fallen leaves or twigs on the ground. It comes to life in the spring. Especially wet spring conditions increase the likelihood of the disease becoming problematic, as the spores more easily spread in wet weather. Infection begins immediately at bud break with more mature leaves able to stave off the fungi.

Damage

• The first signs of damage occur in the early part of the summer as bulges or blisters develop on the upper surface of the leaves along with the accompanying depression on the underside. The depressions often appear light green or yellow and then turn gray as the leaves age. Eventually, the damaged leaves fall and the entire tree may defoliate prematurely. A leaf blister infection is primarily a cosmetic problem and rarely threatens the oak's overall health.

Management

• Oak leaf blister usually does not require chemical control. If chemical applications are utilized, the spraying must occur before bud break in the spring. Complete coverage of the entire tree is vital. Cultural control methods include raking and destroying the fallen leaves and twigs of infected trees in the fall, which minimizes the likelihood of reinfection in the spring.