Introduction
Oak leaf blister caused by the fungus Taphrina caerulescens
is a common disease affecting many species of oaks. Members of the
red oak group are particularly susceptible to infection. Disease development
is favored by cool, wet springs and, in years when such conditions
occur, noticeable leaf deformity results. White oaks are rarely infected,
even in years with cool, wet springs. Heavy infections of red oaks
impair their appearance but do not endanger the tree health.
Symptoms
Symptoms appear in early summer as yellow, blisterlike,
circular, raised areas, 1/16 to 1/2 inch in diameter. The
blisters are scattered over the upper leaf surface with
corresponding gray depressions on the lower surface. They
turn from yellow to reddish brown with pale yellow
margins, then become dull brown with age. Several
blisters may merge and cause the leaves to curl.
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Figure 1: Oak leaf blister
symptoms on upper and lower leaf surfaces.
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Figure 2: Oak leaf blister
symptoms.
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Disease cycle
By midsummer, microscopic ascospores are produced by the fungus
on the upper epidermis of the leaf. Expelled asci and ascospores sometimes
cover the upper and lower surfaces of the blister giving them a white
or light tan, powdery appearance. Some of these spores are carried
by wind and rain to the buds and become lodged under the bud scales.
Here they overwinter. The following spring, they germinate and cause
new infections. Infection occurs in the spring when tender, young
leaves are exposed. Cool, wet weather is required for ascospore germination
on young leaves, and if these conditions prevail, severe infection
can occur. If weather conditions are not favorable for spore germination
shortly after bud break, only minor infection will occur. As the leaves
mature, they become more resistant to infection.
Management Strategies
This disease does not pose a threat to
tree health but can mar the tree's appearance. In special cases where
it is highly desirable to prevent the unsightly infections, a single
application of chlorothalonil, maneb, or mancozeb in early spring
just before the buds begin to swell will effectively manage this disease.
Fungicides will not be effective if applied after bud break.
Homeowners are strongly discouraged from
trying to treat large landscape trees. If treatment is required, consider
hiring a professional applicator.
Updated, SLJ, 3/05
This publication contains pesticide recommendations. Changes in pesticide
regulations occur constantly, some materials mentioned may no longer
be available, and some uses may no longer be legal. All pesticides distributed,
sold, and/or applied in New York State must be registered with the New
York State Department of Environmental Conservation (DEC). Questions
concerning the legality and/or registration status for pesticide use
in New York State should be directed to the appropriate Cornell Cooperative
Extension Specialist or your regional DEC office. READ THE
LABEL BEFORE APPLYING ANY PESTICIDE. __________________________________________________________________________________
The Plant Disease Diagnostic Clinic
at Cornell University is located at 334 Plant Science Building,
Ithaca, NY, 14853. Phone: 607-255-7850, Fax: 607-255-4471,
Email: kls13@cornell.edu
or slj2@cornell.edu |