of Rhode Island GreenShare Factsheets
Red Mite & Two-Spotted Spider Mite
red mite is an introduced pest in the US. It is a pest of nut,
pome and stone fruits, as well as some berries, damaging leaves
and causing fruit russetting. All active stages of the European
red mite injure the foliage by feeding with piercing mouthparts
and removing cell contents, including chlorophyll. Moderate to
high numbers of mites can cause the leaves to initially turn
pale, then bronze as feeding continues. Heavy mite feeding early
in the season can reduce tree growth, yield, and also affect
fruit bud formation for the following year. Some apple cultivars,
such as 'Red Delicious' and 'Braeburn', are especially prone
to mite buildup and injury.
female mites are brick red with white spots at the base of six
to eight hairs on their back. The male mite is more slender and
lighter in color than the female, with a more pointed abdomen.
Eggs are red, globular and somewhat flattened (onion-shaped)
with a slender stalk on the upper side.
red mites overwinter as eggs laid in roughened bark around the
bases of buds and spurs on small branches. During the summer,
eggs are laid on the underside of leaves. Egg hatch in the spring
is closely correlated with bud development and begins close to
the tight cluster stage. During the summer, eggs require 7 to
14 days to hatch. European red mites can have six to eight generations
per year, depending on the temperature. Summer generations may
develop in as few as 14 days.
for mites, examine five hardened-off leaves from each of four
scaffold limbs per tree. Commercial orchardists should examine
at least five trees per acre. Certain varieties, such as Red
Delicious, are more likely to develop large numbers of mites,
so be sure to make samples representative of the varieties in
the orchard. Using a hand lens, count all active stages of pest
and predatory mites. Predatory mites are more active and are
tear-drop shaped. Determine the average number of mites per leaf.
The economic threshold for the mites varies with the time of
year. A miticide is recommended early in the year (until April
1) if numbers of active mites exceed an average of five per leaf,
during April and May when mite numbers exceed 10 per leaf, or
the rest of the season if mite numbers exceed 15 per leaf.
mites are rarely a problem on backyard apple trees. Predatory
mites help to maintain the European red mite at nondamaging levels.
This mite is considered a secondary pest, as it typically only
builds to damaging levels after its natural enemies have been
depleted by insecticide applications used to control codling
moth or other pests. Minimizing insecticide usage and selecting
insecticides that are least toxic to beneficial organisms will
help to minimize problems with this mite.
mite eggs should be controlled through the use of a delayed-dormant
oil treatment, anytime between just before bud swell until 12
mm (1/2 inch) green. Control with dormant oil improves the closer
to egg hatching.
of mites during the growing season is based on scouting and the
use of miticides or summer oil treatments as needed. Often when
heavy summer infestations exist, a second miticide treatment
may be required 10 to 14 days later. Horticultural oils provide
an alternative to traditional synthetic miticides, are able to
kill all mite life stages, and are less toxic to the applicator.
While effective control can be obtained with summer horticultural
oil treatments, caution is advised as these may be incompatible
with some other pesticides within seven to ten days of application
(particularly products containing sulfur and the fungicide Captan),
are phytotoxic at higher temperatures (above 90 degrees F and
high humidity), and may affect fruit finish on some varieties.
spider mite is widely distributed and a common pest of orchards
and nursery plants. When environmental conditions are hot and
dry, spider mites multiply rapidly and become a pest of fields
crops such as corn, soybeans and cotton. Initial infestations
tend to occur in fields bordering clover fields or grassy areas.
Field perimeters and corners tend to exhibit the earliest symptoms
of infestation. Dispersal over a wide area occurs when spider
mites are carried on a balloon of their webbing by the wind.
spider mites feed on the underside of the foliage with sucking
mouth parts and may be very destructive when abundant. Under
hot and dry field conditions, spider mites thrive on plants that
are under stress. The juices which the mites obtain from stressed
plants are rich in nutrients and the mites multiply rapidly.
spider mites are only about .35 mm (1/60 inch) in length, and
have a black spot on each side of their bodies, which range in
color from white to light red. The eggs of the mites appear like
small clear or pale marbles when viewed through a hand lens.
spider mites overwinter as adult females. Egg laying begins in
late April or May; the eggs hatch in five to eight days into
the protonymph stage, which later molts to a deutonymph stage.
These nymph stages have four legs. The time from egg to adult
normally requires about three weeks, but may take less time under
hot and dry conditions. Depending on weather conditions, 5 to
10 generations may occur within a growing season. Spider mite
reproduction and population multiplication will persist until
cool weather of late summer leads to a reduction of population
the degree of a spider mite infestation, it is important that
one recognize the stippling or speckled effect on green foliage
which is the early sign of mite feeding. It is essential to use
a good hand lens to view the relative abundance of mites in egg,
nymph and adult stages.
are optimal for spider mite outbreaks, early detection facilitates
timely and effective treatment. Since mite development is linked
to host plant stress, cultural practices and varieties which
limit plant stress in times of drought will also minimize the
development of spider mites. Narrow-range oil sprays should provide
effective control. Twospotted spider mites are known to have
developed resistance to miticides quite rapidly if a miticide
is applied repeatedly to a population. Alternate miticides and
avoid unnecessary spraying.
from Ric Bessin, University of Kentucky College of Agrictulture
and Harold Willson, Ohio State University Extension, 1999
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
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