Importance. -- Because most of the affected leaves remain on
the tree, oak leaf blisters do not cause losses under forest conditions.
Affected trees may appear unsightly, but there is little damage.
the Fungus. --
The mycelium occurs intercellularly in the leaf tissue. Dome-shaped,
microscopic, fungus cells are formed beneath the cuticle, usually on
the upper leaf surface. The distal cell becomes the sac (ascus) in which
eight ascospores are formed.
the Injury (figure 68). --
Affected leaves develop many blisters on the upper surface. The blisters
are round, raised, wrinkled and vary in color from yellow to purple.
The leaf is depressed on the corresponding lower surface.
Spores (ascospores) of the fungus are produced on the surface of the
blisters. The spores are carried by the wind to bud scales where they
remain over winter. In the spring when the buds are expanding, the fungus
enters the leaf through the natural leaf openings (stomata) and the
cycle is complete.
Collect and dispose of leaves. Plant or manage for resistant oaks such
as pin or Shumard. Properly timed fungicide sprays can control this