Introduction
Azalea gall is a problem of widespread occurrence in this
country. Pale green, pink, white, or brown fleshy galls,
caused by the fungus Exobasidium vaccinii, may
develop on leaves, branch tips, flower parts, and even on
seedpods. 'Pinkster apples' is a term applied to these
abnormal growths by those who enjoy them as a food
delicacy. Exobasidium vaccinii also infects
species of Vaccinium including cranberries where
it produces bright red, swollen spots on the leaves and
fruits. Infected stems become thickened.
Symptoms
The fungus overwinters within the infected plant. In
the late spring and early summer, a whitish coating
appears on the swollen plant tissue. This coating is
composed of many microscopic fungal structures which
produce spores capable of infecting more plants during
moist weather. This disease is not usually a serious
problem unless wet conditions prevail for long periods of
time.
Figure 1: Foliar symptoms
of azalea leaf gall disease. (provided
by the Plant Disease Diagnostic Clinic,
Cornell University) |
Figure 2: A close up of a leaf gall on azalea .
(provided by the Plant Disease Diagnostic
Clinic, Cornell University) |
|
Disease Cycle
The disease develops on the leaves of azalea. The severity of
symptoms varies depending on the weather conditions. Spores are produced
on the leaves during the spring and summer. The spores are dispersed
on air currents and splashed by rain drops on to healthy leaves where
they can cause new infections. This normally occurs during cool, wet
weather. The symptomatic galls are not visiable until the following
spring.
Management Strategies
To control this problem, the galls should be hand picked and destroyed
before they turn white. Most native and horticultural azalea and rhododendron
plants are susceptible. Some species and cultivars are more susceptible
than others. Rhododendron maxium L., R. catawbiense Michx, and their hybrids, are listed as being
particularly susceptible, as are the Indica azalea group. Susceptible
plants growing in poorly aerated soils are more subject to infection
by the fungus than those growing in well-aerated soils.
Last updated, KLS, 8/99
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
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