From apples to zucchini – no matter what types
of plants you grow – it's likely spider mites will
attack. The most common spider mite, the twospotted spider mite (Tetranychus
urticae), has been recorded on more than 300 species of plants,
including all of the tree fruit crops, as well as small fruits,
vegetables, and ornamentals.
first sign of infestation by twospotted spider mite is usually a
chlorotic, stippled appearance on the leaves, although this may not be
as apparent on thick-leaved plants. As the mites feed on the underside
of leaves, they remove leaf cell contents, including the chlorophyll
that gives the leaves their green color. Without the chlorophyll, those
empty cells appear whitish or bronze. Heavily infested leaves turn
completely pale, dry up, and fall off. Large populations can severely
defoliate or kill plants.
The mites also produce fine silken webs over which to crawl. The
undersurfaces of leaves are often completely covered with webbing. When
the mites are numerous, their webbing can cover foliage and flowers,
detracting from the appearance of the plant.
Spider mites are not insects but are more closely related to spiders. These
arachnids have four pairs of legs, no antennae and a single, oval body region.
Most spider mites have the ability to produce a fine silk webbing. Spider mites
are very tiny, being less than 1/50 inch (0.4mm) long when adults.
- Spider mites are common plant pests. Symptoms of injury include
flecking, discoloration (bronzing) and scorching of leaves. Injury
can lead to leaf loss and even plant death.
- Natural enemies include small lady beetles, predatory mites,
minute pirate bugs, big-eyed bugs and predatory thrips.
- One reason that spider mites become a problem is insecticides that
kill their natural predators.
- Irrigation and moisture management can be important cultural
controls for spider mite
Spider mites are common pest problems on many plants around yards and
gardens. Injury is caused as they feed, bruising the cells
with their small, whiplike mouthparts and ingesting the sap. Damaged
areas typically appear marked with many small, light flecks, giving the
plant a somewhat speckled appearance.
Following severe infestations, leaves become
yellow and discolored, producing an
unthrifty gray or bronze look to the plant. Sometimes there can be a lot
of very fine webbing on the plant foliage. Foilage may
ultimately become scorched and drop prematurely. Spider mites frequently
kill plants or cause serious stress to them.
Generally mites feed on the undersides of leaves. They use
their sucking mouthparts to remove sap from plants, giving the upper leaf
surface a speckled or mottled appearance. Leaves of mite infested plants may
turn yellow and dry up, and plants may lose vigor and die when infestations are
severe. The undersides of affected leaves appear tan or yellow and have a crusty
texture. Heavy infestations of the two-spotted spider mite produce fine webbing
which may cover the entire plant.
Spider mites (Family: Tetranychidae) are classed as a type of
arachnid, relatives of insects that also includes spiders, ticks,
daddy-longlegs and scorpions. Spider mites are small and often difficult
to see with the unaided eye. Their colors range from red and brown to
yellow and green, depending on the species of spider mite and seasonal
changes in their appearance.
The most important spider mite is the twospotted spider mite
(Tetranychus urticae). This mite attacks a wide range of garden
plants, including many vegetables and flowers. The twospotted spider mite is
also the most important species on house plants. It is a prolific
producer of webbing.
Twospotted spider mites range in color from light yellow or green to
dark green or brown. All have two dark spots visible on the
abdomen. Males are smaller and more active than females and have a
narrower body with a more pointed abdomen, and larger legs. Females lay
relatively large eggs in webbing on the underside of the leaves. Each
female produces up to 19 eggs per day and a total of up to 120 eggs,
depending on the host plant and temperature. The spherical eggs are
transparent when first deposited, but gradually turn yellowish. The
larvae that hatch from these eggs after 3-15 days (depending on
temperature) are colorless and have only 6 legs. The next two nymphal
stages are pale yellowish to green with 8 legs, and the two dark spots
can be seen. The mites may mature into adults in as few as 5 days during
hot, dry weather.
Many spider mites produce webbing, particularly when they occur in
high populations. This webbing gives the mites and their eggs some
protection from natural enemies and environmental fluctuations. Webbing
produced by spiders, as well as fluff produced by cottonwoods, often is
confused with the webbing of spider mites.
The twospotted spider mite is an example of a 'warm season' mite. This pest
has been reported from over 180 host plants including field crops, ornamental
plants, house plants and weeds.
The females overwinter in the soil or on host plants. The females become
active in April and May when they seek out the undersides of leaves on suitable
hosts. Each female may lay over 100 eggs. A single generation may require as
much as 20 to as few as five days, depending on the temperature. These mites
prefer hot, dry weather and often do not reach damaging populations in cool,
In the summer, the adults and nymphs are white with two greenish spots.
However, overwintering females usually turn reddish-orange and can be mistaken
for other mite species.
Outdoors, twospotted spider mites overwinter as females resistant to
low temperatures. These females are bright orange or red and do not
feed. Development stops
when temperatures are below about 55°F.
The eight-legged female mites are
yellow to dark green with two to
four dark dorsal spots as shown below:
R. Bessin, Univ. of Kentucky
of the biggest problems with recognizing that spider mites are causing a
problem is the fact that they are small – usually only 1/50 inch (0.5
mm) long when mature – and they spend most of their time on the
underside of the leaves. Typically mites are discovered only when damage
on the plant becomes noticeable.
Life Cycles and Habits
Spider mite species seem to be warm weather or cool weather active pests.
Two-Spotted spider mites do best in dry, hot
summer weather. Spider mites develop from eggs, which usually are laid near the veins
of leaves during the growing season. Most spider mite eggs are round and
extremely large in proportion to the size of the mother. Left:
Twospotted spider mites, with eggs.
The eggs hatch in days to weeks into the
first stage, called a larva. Larvae are round bodied and have only three pairs
of legs. The larvae feed for a few days, seek a sheltered spot to rest and then
molt into the first nymphal stage. The first nymph now has four pairs of legs.
The first nymphs feed a few days, rest and molt into the second nymph. The
second nymphs feed, rest and molt into the adult stage. The males are usually
the size of the second nymph and have pointed abdomens. The females have rounded
abdomens and are the largest mites present.
Males are smaller with more pointed abdomens. The tiny,
spherical, eggs are laid on the undersides of leaves, often under the webbing
produced by the mites. A six-legged, colorless larva that emerges resembles the
nymph and adult, but is only the size of an egg. Both of the eight-legged
nymphal stages look like the adult, but are smaller and not sexually mature.
Under optimum conditions of high temperature and low humidity, the life cycle
may be completed in 7 days. Females can lay 200 eggs.
Most spider mites spend the winter in the egg stage but the twospotted spider
mite overwinters as adult females resting in protected places.
There is some variation in the habits of the different mites that
attack garden plants, trees and shrubs. Outdoors, the twospotted spider
mite and honeylocust spider mite survive winter as adults hidden in
protected areas such as bark cracks, bud scales or under debris around
the garden. Other mites survive the cool season in the egg stage. As
winter approaches, most mites change color, often turning more red or
orange. This habit may be why they are sometimes called "red
Most spider mite activity peaks during the warmer months. They can
develop rapidly during this time, becoming full-grown in as little as a
week after eggs hatch. After mating, mature females may produce a dozen
eggs daily for a couple of weeks. The fast development rate and high egg
production can lead to extremely rapid increases in mite populations.
Other species of spider mites are most active during the cooler
periods of the growing season, in spring and fall. This includes the
spruce spider mite and most of the mites that can damage turfgrass.
These cool-season spider mites may cease development and produce dormant
eggs to survive hot summer weather.
Dry conditions greatly favor all spider mites, an important reason
why they are so important in the more arid areas of the country. They
feed more under dry conditions, as the lower humidity allows them to
evaporate excess water they excrete. At the same time, most of their
natural enemies require more humid conditions and are stressed by arid
conditions. Furthermore, plants stressed by drought can produce changes
in their chemistry that make them more nutritious to spider mites.
Early detection of spider mites, before damage is noticed,
is important. The tiny spider mites can be detected by taking a piece of
white paper or cardboard and striking some plant foliage on it. The mites
can be seen walking slowly on the paper. If 10 or more mites per sample are
common, controls may be needed.
Various insects and predatory mites feed on spider mites and provide
a high level of natural control. One group of small, dark-colored lady
beetles known as the "spider mite destroyers" (Stethorus
species) are specialized predators of spider mites. Minute pirate bugs,
big-eyed bugs (Geocoris species) and predatory thrips can be
important natural enemies.
A great many mites in the family Phytoseiidae are predators of spider
mites. In addition to those that occur naturally, some of these are
produced in commercial insectaries for release as biological controls. Predatory mites
often have fairly high requirements for humidity, which can be limiting.
Most suppliers provide information regarding use of the predator mites
that they carry.
In addition to predatory mites there are numerous
insects (lacewings and lady beetles) that prey on spider mites. If predators are used, do not apply pesticides that will
Since rainy weather
seems to knock off spider mites, using a forceful jet of water from a
hose (syringing) can perform the same task. A regular syringing can keep
spider mites under control on most ornamental plants in the landscape.
This technique also helps conserve natural predators.
Adequate watering of plants during dry conditions can limit the
importance of drought stress on spider mite outbreaks. Periodic hosing
of plants with a forceful jet of water can physically remove and kill
many mites, as well as remove the dust that collects on foliage and
interferes with mite predators. Disruption of the webbing also may delay
egg laying until new webbing is produced. Sometimes, small changes where
mite-susceptible plants are located or how they are watered can greatly
influence their susceptibility to spider mite damage. Use of overhead-sprinkler irrigation may provide some short-
term relief of mite infestations.
Above: Twospotted spider mite injury to eggplant.
One reason that spider mites become problems in yards and gardens is
the use of insecticides that destroy their natural enemies. For example,
carbaryl (Sevin) devastates most spider mite natural enemies and can
greatly contribute to spider mite outbreaks. Malathion can aggravate
some spider mite problems, despite being advertised frequently as
effective for mite control. Soil applications of the systemic
insecticide imidacloprid (Merit, Marathon) have also contributed to some
spider mite outbreaks.
Many insecticides used for control of insect
pests severely reduce numbers of beneficial insects that keep mite populations
in check. Therefore, apply insecticides only as-needed, rather than at regularly
scheduled intervals. When possible, select pesticides which will have the least
impact on beneficial insects.
"Soft Pesticides" Most
spider mites can be controlled with insecticidal oils and soaps. The
oils, both horticultural oil and dormant oil, can be used. Horticultural
oils can be used on perennial and woody ornamentals during the summer at
the 1 to 2 percent rate. Higher rates of horticultural oil (3 to 4
percent) or dormant oil are useful for killing mite eggs and dormant
adults in the fall and spring. The insecticidal soaps are useful in the
warm season. Remember that mites are very tiny and soaps and oils work
by contact only. Therefore, thorough coverage of the plant is necessary
for good control.
Miticides Spider mites are
usually not killed by regular insecticides, so be sure to check the
pesticide label to see if "miticide" is present. Pesticides
claiming "for mite suppression" are usually weak miticides and
will not perform well. There are few products available to the
homeowner. Dicofol (=Kelthane) is registered for over-the-counter use
but is difficult to find. Acephate (=Orthene), dimethoate (=Cygon),
chlorpyrifos (=Dursban), diazinon, disulfoton (=Di-syston), and
malathion have over-the-counter product labels but are considered weak
Avermectin (=Avid), bifenthrin (=Talstar), dienochlor (=Pentac),
fenbutatin-oxide (=Vendex), fluvalinate (=Mavrik), oxamyl (=Vydate),
oxydemeton-methyl (Metasystox-R), oxythioquinox (Morestan), and
propargite (=Omite) are restricted use pesticides available only to
(Control Strategies provided by Ohio State University Extension.)
Chemical control of spider mites generally involves pesticides that
are specifically developed for spider mite control (miticides
or acaricides). Few insecticides are effective for spider mites
and many even aggravate problems. Furthermore, strains of spider mites
resistant to pesticides frequently develop, making control difficult.
Because most miticides do not affect eggs, a repeat application at an
approximately 10- to 14-day interval is usually needed for control.
Table 1 includes a summary of pesticides that may be useful for managing
Resistance to pesticides has increased the difficulty of
controlling of these pests. Because mites primarily occur on the undersides of
leaves, applications of contact miticides need to be directed at both the lower
and upper leaf surfaces. Mite eggs are resistant to some miticides, so repeated
applications are often necessary to control infestations.
Chemical control is often the best option for battling spider mites.
Frequent applications of insecticidal soap can be very effective. Soap
has no residual activity and only affects the mites it is sprayed
directly on, so thorough coverage of the foliage and repeated
applications are essential. Most of the mites are on the underside of
the leaves, so that's where the soap spray needs to be applied.
Insecticidal soaps are very effective and should be the first choice
for most spider mite problems. However, other chemicals with residual
activity can be used when there is no danger of children or pets
contacting the leaves. Most insecticides no longer work against spider
mites because of resistance problems. The product ISOTOX IV has both an
insecticide and a miticide and can be used on outdoor ornamental plants.
Products called miticides (or acaricides) are made to control spider
mites, but these products can be hard to find or are not sold to