| Spidermites are among the most serious
pests of ornamental plants. Spidermites are too small to examine
without a magnifying glass. They feed on the underside of leaves
by piercing plant tissue and sucking the juice. Because of their
small size and feeding habits, spidermites may be overlooked until a large
population develops and serious damage occurs.
Description
Spidermites are more closely related to spiders than to insects.
Adult spidermites are eight-legged with soft, oval bodies. The females
are about the size of the period at the end of this sentence, and the males
are slightly smaller. Spidermites vary in color according to species.
Green, orange, red, brown, and black are common colors. Adult females
lay round eggs that hatch into six-legged larvae. Immature spidermites
develop through a series of nymphal stages before becoming mature adults.
Many generations occur per season. Two-spotted spidermites reproduce all
season long or year round in greenhouses. Southern red mites and
spruce mites are active only in the spring and fall.
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Spidermite webbing on marigolds.
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Damage
Plants infested with spidermites have off-color (yellowish or bronzed)
foliage. Close inspection reveals leaves with a speckled or stippled
appearance. Leaves infested with two-spotted spidermites may have a fine
web underneath. In heavy infestations, the web may cover the whole plant.
Heavy mite infestations result in premature leaf drop and plant death.
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Spidermite damage to holly:
affected branch on left, healthy on right.
Note spidermite infestation on left branch.
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Host Plants
Some of the most common plants infested by spidermites are azaleas,
boxwoods, carnations, hawthorns, hollies, maples, violets, pyracanthas,
oaks, privets, roses, snapdragons, junipers, and spruce.
Control
Close and regular inspection of plants is essential to the control of
spidermites. Remember, mites feed on the underside of leaves, so
thorough application of pesticides to the undersurface of leaves is necessary.
If the pesticide label permits it, another application in 7 to 10 days
may be needed to kill mites that were in the egg stage during the first
application, depending on the pesticide.
Look for phytotoxicity (plant burn) information on the pesticide label.
Use only on plants specified on the label; avoid using on plants which
the label lists as damaged by the product.
Table 1 lists pesticides recommended by the 2001 Alabama Pest Management
Handbook for homeowner use. If spidermites continue to be a problem,
alternate pesticides once or twice during the season.
Table 1. Homeowner Control
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Chemical
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Amount To Use Per Gallon Of Water
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diazinon formulations
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See Label
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dicofol
KELTHANE
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See Label
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dienochlor
PENTAC
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See Label
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horticultural oil, such as
SUNSPRAY ULTRA FINE
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See Label
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insecticidal soap
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2 teaspoons
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Use pesticides only according to the
directions on the label. Follow all directions, precautions, and restrictions
that are listed. Do not use pesticides on plants that are not listed on
the label.
The pesticide rates in this publication are recommended
only
if they are registered with the Environmental Protection Agency and the
Alabama Department of Agriculture and Industries. If a registration is
changed or cancelled, the rate listed here is no longer recommended. Before
you apply any pesticide, check with your county Extension agent for the
latest information.
Trade names are used only to give specific information.
The Alabama Cooperative Extension System does not endorse or guarantee
any product and does not recommend one product instead of another that
might be similar.
For more information, contact your county Extension office. Look
in your telephone directory under your county's name to find the number.
Issued in furtherance of Cooperative Extension
work in agriculture and home economics, Acts of May 8 and June 30, 1914,
and other related acts, in cooperation with the U.S. Department of Agriculture.
The Alabama Cooperative Extension System (Alabama A&M University and
Auburn University) offers educational programs, materials, and equal opportunity
employment to all people without regard to race, color, national origin,
religion, sex, age, veteran status, or disability.
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