Reports on Plant Diseases |
RPD No. 663 - Oak Leaf Blister
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September 1999
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[ Symptoms ] [ Disease Cycle
] [ Control ] [ Table 1 ] [
Table 2 ]
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Leaf blister or leaf curl of oaks is caused by the fungus Taphrina
caerulescens. This common disease occurs worldwide on about 50 species
of oaks (Quercus spp.) mainly in the red and white oak groups.
Ten species of oaks are known to become infected in the Midwest (Table
1) with red oak especially susceptible. In Illinois, the disease usually
appears only during cool wet springs seldom causing serious damage. Heavy
infections of red and other oaks may be unsightly but does not endanger
the life of the trees.
Scientists believe that the causal fungus is actually a group of biologically
distinct organisms that have become specialized in the oak species which
they infect. The genus Taphrina is also responsible for leaf blisters
or leaf curls on many other plants (Table 2) with the main economic importance
on peaches, plums and cherries.
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Figure 1.
Leaf blisters on lower surface of red oak leaf (courtesy of Mark Gleason).
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Symptoms
Figure 2.
Leaf blister conspicuous due to raised, wrinkled appearance; diseased
areas turn brownish with age. (IL Natural History Survey photo).
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In late spring or early summer, young partially grown leaves
develop circular, raised, wrinkled, yellowish white spots on upper surfaces
with yellowish brown to gray depressions of the same size on the corresponding
lower surfaces (Figure 1). The blisters are 3 to 30 millimeters in diameter
and scattered over the leaf surface. Lesions later turn reddish brown with
pale yellow margins and finally become a dull brown with age. Several blisters
may merge which involve much or all of a leaf forcing it to curl (Figure
2) and can cause premature defoliation. |
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Disease Cycle
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In the Midwest the Taphrina fungus overwinters as microscopic
ascospores lodged under the bud scales. The spores germinate in the spring
as the buds break open and the young leaves are expanding. The germ tubes
of the spores penetrate young leaves directly through the cuticle as emerging
hyphae grow intercellularly mainly between the epidermal cells. A layer
of asci forms in late spring or early summer between the outer epidermal
wall and the cuticle. The asci, which contain the ascospores, push through
the cuticle and rupture releasing tremendous numbers of ascospores (Figure
3). The expelled spores cover the surface of the blisters giving them
a white to light tan, powdery appearance. They are spread about by air
currents, splashing rains, and insects to the buds, where they become
lodged under the bud scales, thus completing the disease cycle. The causal
fungus may occasionally cause one or more secondary cycles of disease
when buds open unseasonably in late spring or summer. Mature leaves are
resistant to infection.
In the southern states the Taphrina fungus overwinters as resting
ascospores on the buds, twigs and branches of oaks. The disease is more
common and severe in the southeastern and Gulf states than it is in the
Midwest, especially on the southern red oak, conceivably because populations
of ascospores remain higher throughout the winter.
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Figure 3.
Taphrina caerulescens, cause of leaf blister or leaf curl of oaks; under
high-power microscope: (a) vertical section of upper surface of leaf
showing layer of epidermal cells and compact, palisade layer of asci,
some containing ascospores, which have ruptured leaf cuticle; (b) two
asci, one with 8 ascospores, other - -ascospores budding, (c) ascospores
budding (forming secondary spores); (d) late budding of ascospores;
(e) two ascospores germinating.
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Control
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Since this disease is much more unsightly than harmful to oak trees, no
control measures are usually suggested.
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Collecting and composting or burning the leaves as they drop may be of
some benefit in reducing the inoculum for the following spring.
- A single dormant fungicide spray, applied before the buds
begin to swell in early spring, will control the disease but is not commonly
recommended. Fungicide sprays applied after budbreak are ineffective.
Suggested fungicides to use are given in Illinois Homeowner's Guide to
Pest Management. This circular is revised annually.
Table 1
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Oaks grown in the Midwest wich
are susceptible to leaf blister caused by Taphrina caerulescens
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White oak
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Pin or Spanish oak
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Scarlet oak
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Chinquapin or dwarf chestnut oak
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Jack or northern pin oak
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Post Oak
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Laurel or single oak
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Black or yellow-barked oak
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Bur or mossy-cup oak
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Blackjack or jack oak
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Table 2
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Other plants grown in the Midwest
infected by species of Taphrina
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River, silver or soft maple
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American hophornbeam |
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Red maple (Black leaf blister), (Leafblight)
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Bigtooth or large-toothed aspen (Catkin deformity) |
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Hard or sugar maple (Brown leaf blister)
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Black poplar |
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Four-speckled or white alder (Catkin deformity)
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Black or Lobardy poplar |
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Mountain or water birch (Witches' broom)
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Quaking or trembling aspen |
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Canoe, paper or white birch (Red leaf blister or leaf
curl)
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Tall cinquefoil |
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American hornbeam
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Common cinquefoil |
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American filbert or hazelnut
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Dwarf sumac |
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Brittle or fragile fern (Leaf gall)
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Skunkbush |
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Fern, no common name
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Marsh or meadow fern (Leaf gall) |
| American elm |
Cork or rock elm |
| Red or slippery elm |
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For further information concerning diseases of woody ornamentals, contact
Nancy R. Pataky, Extension Specialist and Director of the Plant Disease Clinic,
Department of Crop Sciences, University of Illinois at Urbana.
University of Illinois Extension provides equal
opportunities in programs and employment.
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