Oak Leaf Blister on Willow Oak: Identification and Dormant-Season Control

Diagnosing the Raised Growths

Brown, solid, raised bumps on 80% of leaves are oak leaf blister (Taphrina caerulescens), a fungal disease. Water and willow oaks are highly susceptible; pin and Shumard oaks are resistant.

Disease Cycle

Spores overwinter in bud scales. Infection occurs only during early spring leaf expansion. Summer symptoms are the result of spring infection.

Control Window

Single dormant fungicide application (January–mid-March) coats buds and prevents infection. Effective products:

• Chlorothalonil (Bravo, Daconil)
• Mancozeb, captan, or tri-basic copper sulfate

Apply just before bud break for best coverage.

Impact

Mostly cosmetic. Severe cases may cause early leaf drop but rarely threaten tree health.