From: James R. Baker and Stephen B. Bambara, Extension Entomologists
We continue to receive samples of woody ornamentals infested with armored scale insects. Even though these pests are perennial and have not just suddenly appeared, dormant applications of horticultural oils are effective for armored scale insect control and soon most ornamentals will be hardening off for the winter (for maples it is best to wait until mid January before treating with oils) so this is a good time to think about armored scales. Dormant applications of pesticides for mites, aphid eggs and armored scales give horticulturists something to do during the late fall and winter. Euonymus scale, gloomy scale, juniper scale, peony scale, pine needle scale, tea scale, and white peach scale are our most frequently-reported armored scale insects in the landscape and nursery.
Horticultural oils are essentially the same chemical as plant shine
oil, baby oil or mineral oil except that horticultural oils often
have a surfactant that helps keep the oil in suspension. Because
of its relatively low toxicity to humans and low impact on the
environment (when used according to label directions), oils are
considered biorational and the use of oils for pest management has
been accepted by most organic farming certification panels.
Ornamentals and Turf Insect Information Note No. 45 has
additional information on horticultural oils and rates for use on
scales as well as aphids, mealybugs, mites and whiteflies.
Euonymus scale insects are common and sometimes very damaging pests
of euonymus and a few other ornamental plants. Male euonymus
scales have snowy white armor and are sometimes quite conspicuous
against the leaves. Females have gray, oyster-shaped armor and are
less conspicuous. Females and males can be found on stems as well
as on leaves. Ornamentals and Turf Insect Information Note No.
15 provides information on the euonymus scale and its control.
Horticultural oil or Cygon used for euonymus scale suppression
should also control spider mites and other pests of euonymus.
Gloomy scales make the bark of infested maples rough, dark and
unsightly. They also cause twig dieback. Gloomy scales are
armored scales. They overwinter as mated females and the young
scales are produced from May to the middle of August. Gloomy
scales are susceptible to horticultural oils, but infested trees
may be large and difficult to spray. Because the scales build up
in layers, it may be very difficult to obtain good control by
spraying. It is probably better to spend energy getting an
infested tree into good growing condition than to waste energy
spraying with improper equipment. First, submit a soil sample to
the North Carolina Department of Agriculture Soils Laboratory. If
the pH or nutrients are out of balance, the soil should be amended.
Second, if there is another period of prolonged drought stress this
summer, the tree should be irrigated. Third, apply Roundup on the
grass under the tree and mulch the soil to conserve soil moisture
and keep the roots cool. Every effort should be made to enhance
the vitality of the trees. Trees under stress have more simple
sugars (rather than starches) and more free amino acids (rather
than more complex proteins) in the sap. Thus, stressed trees are
more nutritious to the scales than healthy trees. The bark of an
unsprayed tree is often like a microscopic zoo with all sorts of
predaceous mites, predaceous insects, parasitic fungi, parasitic
insects and other organisms as well as the scales. A tree in top
growing condition should be less susceptible to the scales and the
scales will not reproduce as prolifically. As a consequence, the
parasites and predators may control the scales almost completely.
Ornamentals and Turf Insect Information Note No. 60 provides
additional information on the biology and control of gloomy scales.
The juniper scale is a fairly damaging pest. Infested conifers
often have dead or stunted twigs and uneven growth. The juniper
scale insect is a very small (up to 1 mm) armored scale insect.
The armor of the females is circular to oval and is white and
parchment-like. In the center is a light-yellow cast skin of the
earlier female nymph stages. The armor of the male scale is
oblong, white and about 1 mm long. At one end is the pale yellow
cast skin of the crawler stage. Adult males are tiny insects
resembling gnats with four eyes and a tiny waxy tail filament.
Little is known of the biology of juniper scale insects. If they
behave like other armored scales, these scales hatch from eggs laid
by the mother scale under her armor. The tiny crawlers emerge to
crawl about seeking a suitable place to feed. Female scales molt
twice before maturing; male scales molt three times. Males emerge
from the male armor and seek females with which to mate. The males
soon die. Females soon lay eggs for another generation. After
laying eggs, the females die. The armor of both males and females
clings to the infested shrubs long after the scales inside die
(females) or leave (males). They are found on the needles and bark
of Cedrus, junipers, cypresses, spruce and Leyland cypress.
Because they are so small, juniper scales are easily overlooked.
The juniper scale is a debilitating pest of junipers and is
considered an economic pest. Insecticide applications are often
required in commercial nurseries for control. Horticultural oils
or dimethoate (Cygon) should give adequate control of the juniper
scale. Available in the county extension centers are copies of
Ornamentals and Turf Insect Information Note No. 57, the Juniper
Pest Control Calendar.
The peony scale can be quite damaging to its host plants. Infested
plants are often stunted and have noticeable dieback. One of the
more obvious signs of the peony scale is the lower portion of the
armor which adheres to the stems of infested plants long after the
upper armor and body of the insect have fallen away leaving a white
scar. The lower portion of the armor is circular and white (3 to
4 mm in diameter), whereas the upper armor of the live scale blends
in almost completely with the bark. Because the peony scale is an
armored scale, the best chemicals for their control on azaleas,
rhododendrons and camellias are horticultural oils or dimethoate.
The pine needle scale is a small, white, narrow scale insect that
feeds on the needles of ornamental pines. The pine needle scale is
not worth treating if the population is low; however, if there are
many scales on each needle, it may wise to treat with insecticide.
Pine needle scale insects overwinter on the needles as eggs under
the armor of the dead mother scale insect. These eggs hatch in the
spring. Tiny purple crawlers emerge from under the old armor and
settle down on the needles to mature and lay eggs for another
generation which will mature later in the summer and ultimately
produce the overwintering eggs. Pine needle scales are most
damaging to ornamental pine plantings. Austrian and Mugho pines
may be so heavily infested that these shrubs become chlorotic and
suffer premature needle drop. Research performed by Dr. Warren
Johnson at Cornell University has shown that pine needle scale
insects are susceptible to oil sprays. We recommend using a 4
percent oil spray during the winter and a 2 percent oil spray now
and later in the fall.
The tea scale is a serious pest of camellias and Chinese hollies in
North Carolina, but it has also been reported from bottle brush,
dogwoods, euonymus, ferns, mangoes and other ornamental plants as
well. Infestations occur on the leaves, usually on the underside.
Heavily-infested Chinese hollies look unhealthy and may drop their
leaves prematurely. Tea scale females lay from 10 to 16 eggs each.
The eggs hatch in one to three weeks, depending on the weather.
The crawlers emerge and migrate to the newer foliage of the plant
and begin to feed. In about two months, the new generation of
scales mature and begin to lay eggs. The hatching of the eggs
occurs throughout the year, although development is much slower in
cold weather than in warm weather. Cygon (dimethoate) and several
horticultural spray oils are on the market for the control of tea
scale. However, do not use dimethoate on hollies as it can cause
leaves to drop off. These insecticide sprays should be directed
thoroughly to the underside of the leaves. The best time to spray
insecticide is in the spring after the cold weather has passed,
although it would be favorable to apply one of these insecticides
now and again in 14 days. Two applications 14 days apart should be
sufficient. Ornamentals and Turf Insect Information Note No. 54,
the Camellia Pest Control Calendar should be available in the
county extension centers in North Carolina.
White peach scale insects are pests of peaches and related trees as
well as lilac, ligustrum, walnut and other woody plants. White
peach scales can be quite damaging and infested plants may be
stunted and die back or completely killed. Because the white peach
scale is an armored scale insect, it is susceptible to the
horticultural oils. These oils can be used at a growing season
rate from bud break until late December or can be used at a dormant
spray rate during the winter to reduce the overwintering
population. Dr. John Meyer of the Department of Entomology at
North Carolina State University conducted experiments on the
control of white peach scales a few years ago and found that oils
would suppress white peach scales. It is probably best to apply
the oil once, wait two or three weeks, and apply it a second time.
The crawlers of white peach scale can be present in low numbers
throughout the year, but there are distinct peaks of crawler
emergence in early May, mid July, and early September. Another
strategy for control of these insects is to wait until early May
and apply Dursban; some formulations of Dursban are specifically
labeled for white peach scales. White peach scales have two very
effective natural parasites, Encarsia berlesi and Aphytis proclia.
However, large white peach scale populations and shrubs or trees
with dieback indicate that the parasites are not effectively
controlling the pest. Horticultural oils may be preferable because
they probably have less impact on the parasites than Dursban.
Web page last updated on October 17, 1997 by Stephen J. Toth, Jr..
