Scale Insects
Contact: Eric Day, Manager, Insect Identification Laboratory
ENTOMOLOGY PUBLICATION 444-224, August 1996
Scale Insects
Scale insects are a peculiar group and look quite different from
the typical insects we encounter day to day. Small, immobile,
with no visible legs or antennae, they resemble individual fish
scales pressed tightly against the plant on which they are
feeding. There are over l50 different kinds of scales in
Virginia. Many are common and serious pests of trees, shrubs,
and indoor plants.
Damage
Scale insects feed on plant sap. They have long, threadlike
mouthparts (stylets) six to eight times longer than the insect
itself. Feeding by scales slowly reduces plant vigor. Heavily
infested plants grow poorly and may suffer dieback of twigs and
branches. Occasionally, an infested host will be so weakened
that it dies.
Control
Adult scales are protected from insecticides by waxy coverings.
Control measures, therefore, must be aimed at unprotected
immatures (crawlers) or the overwintering stage. Dormant oils
are effective on the overwintering stage of most species, but
they can only be applied in early spring before leaves appear.
During the summer, control requires accurate identification of
the pest species so that hatching dates of crawlers can be
determined. Once the pest is identified and proper timing known,
any one of several common insecticides can be used. Consult your
local Extension Agent for current insecticide recommendations.
Armored Scales
Scale insects can be roughly divided into two groups: armored
scales and soft scales. Armored scales are so named because they
secrete a protective cover over their bodies. Most species
overwinter as eggs beneath the female cover. In spring, eggs
hatch into tiny mobile crawlers which migrate to new feeding
sites. After a few days, crawlers settle, insert their
mouthparts, and begin feeding. Soon they secrete a protective
cover and lose their legs. Large populations can build up
unnoticed before plants begin to show visible symptoms. Our most
common armored scale pests are described and illustrated below.
San Jose Scale
Mature scales are circular, slightly convex, and
smoky black. They are about l/l6 inch across. Under a
magnifying glass, a conspicuous, dark gray, concentric ring is
visible. San Jose scale is perhaps the most widely distributed
and most destructive scale insect pest of fruit trees, shade
trees, and ornamental shrubs in the United States. Over 60 host
plants are known, including apple, pear, peach, cherry, ash,
poplar, lilac, elm, willow, pyracantha, and cotoneaster. There
are at least three generations a year in Virginia; broods often
overlap. When necessary, treat June l0-l5, July l0-l5, and
September l0-l5.
Oystershell Scale
These scales are shaped like the shell of an
oyster. They are chestnut to dark brown, sometimes with lighter
transverse bands. Twigs are often completely encrusted with
scales. This is a common and destructive pest of over l20
different species of fruit trees, shade trees, and woody
ornamental shrubs. Hosts include apple, lilac, dogwood, boxwood,
birch, elm, sycamore, viburnum and many others. There are two
generations per year with crawlers active May l-20 and July l5-
25.
Pine Needle Scale
Mature scales are pure white and shaped like
oyster shells. This is a common and serious pest of ornamental
pines and various spruces. Less preferred hosts include hemlock
and fir. Ornamental plants, Christmas tree plantations, and
nursery stock are more frequently infested than forest trees. In
heavy infestations, needles may be completely whitened by a
continuous layer of scales. There are two generations per year
in Virginia. Crawlers are active between April 20-May 30 and
July l0- 20.
White Peach Scale
Females are circular and white with an orange-
yellow central spot. Males are elongate and pure white with a
slight ridge down the back. White peach scale is a serious pest
of stone fruits, especially peach and cherry. Flowering cherry,
plum, and peach are also infested. There are three generations
per year. Crawlers are active April 25-May l5, July l-l5, and
August 20- September l5.
Euonymus Scale
Females are pear-shaped and blackish-brown.
Males are elongate and white. This is a common and serious pest
of evergreen euonymus, often causing defoliation and dieback.
Pachysandra and bittersweet are also suitable hosts. There are
two generations per year. Crawlers are active May 5-June l0 and
August l-25. When required, four treatments are recommended:
May l0 and 20, and August 5 and l5.
Gloomy Scale
Both sexes are circular, strongly convex, and dark
gray or black. Mature scales have a central, light-gray,
circular right which is visible with a magnifying glass. Gloomy
scale is a common and serious pest of silver maple and red maple.
It is also found on sugar maple, hackberry, elm, boxelder,
sweetgum, redbud, buckthorn, gallberry, mulberry, and soapberry.
There is one generation per year in Virginia with crawlers active
June l0-20.
Obscure Scale
Mature scales are dark gray, often identical to
the color of the bark. Crawlers tend to settle close together,
resulting in patches of scales several layers deep. This is a
serious pest which causes dieback of branches, limbs, and
sometimes entire trees. Oaks, especially pin oak, are the
primary host, but it has also been reported on chestnut, pecan,
beech, English walnut, willow, maple, hickory, and other trees.
Crawlers on red oaks are active in mid-July, but on white oaks in
mid-August.
Juniper Scale
Females are round and dirty-white with yellow
centers. Under a magnifying glass they resemble miniature fried
eggs. Males are also white, but smaller and narrower. Hosts
include junipers, arborvitae, incense cedar, and cypress. There
are two generations annually. Crawlers are active April 5-20 and
June 5-20.
Japanese Scale
Mature scales are grayish white, long, and
narrow. Japanese scale is a pest of maple, privet, boxwood,
holly, Japanese quince, and rose. Use dormant oil sprays or
treat for crawlers every two weeks between June l and September l.
Other Armored Scales
Fern Scale: Males white and narrow; females brown and pear-
shaped. On ferns, African violet, begonia, camellia, citrus, fig,
geranium, hibiscus, liriope, orchids, palms, violet, and many
others. Greedy Scale: Attacks apple, birch, cactus, camellia,
cherry, cotoneaster, English ivy, English walnut, euonymus,
grape, locust, magnolia, maple, oak, palm, pyracantha, redbud,
rose, willow, and many others. Grape Scale: Found on grape,
peach, hickory, and sycamore. Latania Scale: On palms, orchids,
canna, gladiolus, raspberry rose, and other plants. Hemlock
Fiorinia Scale: On hemlock, fir, spruce, and yew. Hemlock
Scale: On hemlock, Douglas-fir, Monterey, yellow, and some other
pines. Elm Scurfy Scale: Found on elm and hackberry. Scurfy
Scale: Attacks pear, apple, quince, cherry, peach, black
raspberry, dogwood, mountain ash, black walnut, elm, hickory,
maple, willow, and others. Dogwood Scurfy Scale: On dogwoods.
Soft Scales
In general, soft scales are larger and more convex than armored
scales. Many resemble miniature tortoise shells. Soft Scales
usually cover themselves with wax, but they lack the detachable
protective cover for which armored scales are named. Most soft
scales overwinter as immature, fertilized females. In spring
they resume feeding, mature, and lay eggs. These hatch into tiny
crawlers. After locating suitable feeding sites, crawlers settle
and begin feeding. Some species lose their legs once they've
settled, but others retain them and are able to crawl short
distances to find suitable overwintering sites in the fall.
Except for soft scales which infest indoor plants, most have only
a single generation per year at our latitude. Our most common
soft scale pests are described and illustrated below:
Magnolia Scale
Our largest scale insect, this species reaches
l/2 inch in length. Color ranges from dark brown to pink-orange
and older scales are covered with a white waxy powder. Large
amounts of a sticky waste product called honeydew are secreted by
the scales. Wasps and ants are attracted to the honeydew and
black fungi called sooty molds grow on surfaces where honeydew
collects. There is one generation per year with crawlers active
from September l-20, much later than most other species.
Tuliptree Scale
This is our second largest scale, reaching l/3
inch in length. Color varies from gray-green to pink-orange,
mottled with black. It is easily mistaken for magnolia scale but
lacks the white, waxy powder. Both tulip tree and magnolia are
attacked and may be seriously weakened. Large amounts of
honeydew are produced. There is one generation per year with
crawlers active September l-20. A single female can produce over
3000 young!
European Fruit Lecanium
Typical scales are l/8 inch long, oval,
and very convex. Color varies considerably with age and host,
but usually they are brown to reddish-brown, smooth and shiny.
The host list of this insect includes a wide range of fruit and
shade trees, shrubs, and other woody ornamentals. Favorite hosts
include peach, cherry, plum, apple, ash, blueberry, black walnut,
boxelder, elm, grape, hickory, locust, magnolia, maple, oak,
redbud, willow, and many others. There is one generation per
year with crawlers active between June l-20.
Oak Lecanium
This species is similar in appearance to European
fruit lecanium. Oak is the favored host, but hickory and birch
are also attacked. There is one generation per year with crawlers
active from May 25-June 25. When necessary, treat June l5 and
20.
Fletcher Scale
Mature scales are shiny, dark brown, and very
convex. They are similar in appearance to European fruit
lecanium and oak lecanium which are close relatives. Arborvitae
and yew are the most frequently attacked hosts, but pachysandra
and Eastern Red cedar are also susceptible. Honeydew excreted by
the scales supports unsightly, sooty molds. There is one
generation per year with crawlers active June 5-25. When
necessary, treat between June l0-l5.
Hemispherical Scale
Mature scales are brown, smooth, glossy, and
very convex (thus the name), with a slightly flared margin. They
measure about l/8 inch in length. Hemispherical scale does not
overwinter outdoors at our latitude and is, therefore, primarily
a pest of houseplants and greenhouse plants. Among the most
commonly attacked host plants are ferns, palms, avocado, begonia,
citrus, chrysanthemum, fig, lily, orchids, and many others. In a
constant indoor environment, reproduction is continuous and
generations overlap. Successful treatment requires two to three
insecticide applications at l0-day intervals. When feasible,
large numbers of these scales can be physically dislodged by
gently wiping the leaves with a dilute mixture of water and
dishwashing detergent. Combine manual and chemical control for
best results.
Brown Soft Scale
Adults are oval, soft, rather flat, and l/8
inch long. Color is usually yellowish-brown or greenish-brown.
Brown soft scale is found indoors throughout the state and
outdoors along the eastern seaboard. It has a very long host
list and is common on gardenia, fern, camellia, oleander, fig,
and many others. Reproduction is continuous with overlapping
generations. Recommended controls are the same as for
hemispherical scale.
Pine Tortoise Scale
Mature scales are shaped like miniature
tortoise shells, thus the name. They are reddish-brown, mottled
with dark spots. Scots, Austrian, jack, and red pines are
preferred, but several other species of pines are susceptible.
There is one generation per year with crawlers active June l0-
July 5. When necessary, treat between June 20-25.
Wax Scale
Immature scales have spots of wax on the back and
around the margin. As they mature, more and more wax is produced
until it eventually covers the entire scale in a thick, white,
irregular coat. Wax scale is found only in eastern Virginia.
Hosts include azalea, blueberry, camellia, Chinese holly,
mulberry, pear, persimmon, plum, quince, and others. There is
one generation per year with crawlers active June l-25. When
necessary, treat June l0-30.
Cottony Camellia Scale,
Cottony Taxus Scale
Long, white, cottony
egg sacs produced by this scale are much more conspicuous than
the scales themselves. After completion of the egg sac, the
female dies, dries up, and falls to the ground. Host plants
include camellia, holly, taxus, rhododendron, hydrangea, maple,
and English ivy. There is one generation per year with crawlers
active June l- l0. When necessary, treat June l0-20.
Cottony Maple Scale
Large, conspicuous, white egg sacs are
produced on the twigs and small branches of host plants. During
summer, immature scales feed on leaves, but they migrate to twigs
as fall approaches. Honeydew excreted by the scales supports
unsightly, sooty mold growth. Cottony maple scale is most common
on silver maple, but also found on other maples, boxelder,
linden, black locust, red mulberry, white ash, apple, beech,
cherry, dogwood, elm, hickory, holly, honeylocust, peach, plum,
sycamore, willow, and others. There is one generation per year
with crawlers active June 5-25. When necessary, treat on both
June l0 and 20.
Cottony Maple Leaf Scale
Conspicuous, cottony egg sacs, similar
to cottony maple scale, but produced on the leaves. Occurs on
maple, dogwood, holly, andromeda, and gum. There is one
generation per year with crawlers hatching June l-l0. When
necessary, treat between June l5-30.
Oak Kermes
Mature scales are tan, globular, and hard. They are
easily mistaken for galls or buds. Oak is the only host. This
species is not particularly injurious to host trees, but, if
necessary, treat between June l0-l5.
Other Soft Scales
Golden Oak Scale: Injurious to young oak trees and older trees
when drought-stressed. Pit-making Scales: Form shallow pits in
the bark of oak and holly. Azalea Bark Scale: On azaleas,
rhododendron, andromeda, hawthorn, poplar, and willow. Calico
Scale: On elm, Zelkova, maple, pyracantha, pear, sweetgum,
Boston ivy, Virginia creeper, dogwood, buckeye, and flowering
crabapple. European Elm Scale: Reddish-brown with a white
fringe. On elms.
Revised by Eric Day. Department of Entomology, Virginia
Polytechnic Institute and State University, Blacksburg, Virginia
2406l-03l9.
