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Introduction
Sooty mold
is a charcoal black fungus that appears as a black coating on the surface
of leaves, fruits, twigs and branches of many deciduous and evergreen
shrubs and trees. This fungus is not pathogenic to plants but obtains its
nourishment from insect honeydew.
Symptoms
Honeydew is a
sweet, clear, sticky substance secreted by insects such as aphids,
mealybugs, scales, and whiteflies. The honeydew drops from the insects to
the leaves and twigs. Wind blown sooty mold spores (seeds) that stick to
the honeydew then have a suitable medium for growth. When spores
germinate, they send out black fungus strands (mycelial threads) that
bring about the discoloration. A heavy coat of black mold may build up on
needles (Figure 1) and twigs over more than one growing season.On leaves, this coat
of mold screens out light and reduces the plants capacity to produce food.
On some trees no obvious damage can be noticed. Shrubs under trees that
are heavily infested with honeydew producing insects may be seriously
damaged or killed because the leaf chlorophyll cannot function properly.
Azalea, Rhododendron, Pieris, Cotoneaster, holly and other low-growing
shrubs, growing under shady conditions are susceptible to serious damage.
Figure 1: Heavy building
of Sooty Mold on needles. |
Figure 2: Sooty Mold on
a
branch. | |
Management Strategies
To prevent sooty mold, control the insects. The insects
involved are small and may be present in large numbers before the black
strands of sooty mold appear. Trees and shrubs should be observed
frequently during the growing season for honeydew and insects. At the
first sign of aphids, mealybugs or whiteflies an insecticide spray may be
used. Insecticides with the active active ingredients such as malathion,
diazinon (Spectracide) or an insecticidal soap are approved for use on
Sooty Mold. Follow the manufacturer's recommended rates for application.
If scale insects are present, consult your county agricultural agent or
professional arborist for the proper time to spray.
Remember --
look for insects not only on the affected plants, but overstory plants as
well for infestation when sooty mold appears.
Sooty mold can be
washed off plants, but unless the causal insects are controlled, it will
reappear.
Last updated, KLS, 10/99
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 |
