Oak Leaf Blister

ANR-945, Web Only, Revised Sept 2003. Jacqueline Mullen, Extension Plant Pathologist and Diagnostician, and Austin Hagan, Extension Plant Pathologist, Professor, Entomology and Plant Pathology, Auburn University

Oak leaf blister is a fungal leaf spot disease caused by the fungus Taphrina deformans. It is a spring disease common in Alabama on all oak species. Severe leaf blister can result in widespread early defoliation. With well-established trees, early defoliation will not cause tree death, but it will reduce tree vigor and aesthetics.

Early symptoms of leaf blister on white oak.

Symptoms. Early in the spring, small, rough (concave-convex) spots will begin to appear as the leaves expand. Gradually, the spots will become pale green in color and somewhat thickened. Older spots are brown or greenish brown. Leaves with numerous spots will fall prematurely to the ground. If well-established trees defoliate before midsummer, they will sometimes leaf out later in the season. When defoliation occurs in the late summer, leaf loss will have little impact on the tree's health.

Persistence and Transmission. Microscopic spores are produced in leaf spots during midspring. These spores are carried by wind and splashing rain drops to bud scales and twigs where they remain in a resting stage until the following early spring. At this time, rain washes the spores onto young leaves where infection takes place. After 2 to 4 weeks, depending on weather conditions, small circular depressions (spots) will begin to develop. Spores produced on these spots will lodge in bud scales and, again, remain dormant until the following spring.

Control. Because oak leaf blister does not seriously affect the overall health of the tree, chemical control measures are usually not recommended. Likewise cultural controls are ineffective because of the nature of the fungus and its method of infection and transmission. The following strategies for limited control of oak leaf blister are recommended:

• Collect and discard fallen leaves.
• On small, newly established or especially valuable specimen oak trees previously damaged by leaf blister, apply a protective fungicide. Apply the fungicide at bud swell.
• The following fungicides are labeled for use on oak to control oak leaf blister: Bordeaux mixture, Daconil Ultrex, Daconil Weather Stik 6F, Rose and Shrub Disease Combo, Dithane M-45 80W, Fore 80W. Always follow label recommendations and precautions.

Trade names are used only to give specific information. The Alabama Cooperative Extension Service does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.

For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.