Oak leaf blister is a fungal leaf spot disease caused by the fungus
Taphrina deformans. It is a spring disease common on all
oak species. Severe leaf blister can result in widespread early
defoliation. On well-established trees, early defoliation will not
cause tree death, but will reduce tree vigor.
Early in the spring, small, rough (concave-convex) spots appear
as the oak leaves expand. The spots 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.
of Robert L. Anderson, USDA Forest Service
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 spring. At this time, rain washes the spores onto young
leaves, where infection takes place. After two to four 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.
oak leaf blister does not seriously affect the overall health of
the tree, chemical control measures are usually not recommended.
Cultural controls tend to be ineffective because of the nature of
the fungus and its method of infection and transmission. On small,
newly established or especially valuable specimen oak trees previously
damaged by leaf blister, apply a protective fungicide at budswell.
from Jacqueline Mullen and Austin Hagan, Alabama Cooperative Extension