E-29-W

Ornamentals & Turf

Department of Entomology

SCALE INSECTS ON SHADE TREES AND SHRUBS

Clifford S. Sadof, Extension Entomologist

Scale insects are common pests of shade trees and Soft scales, are not covered by a waxy shell. Crawl-
shrubs. More than 60 different kinds occur in Indiana, yet ers that hatch from eggs in mid-summer will usually crawl
they are often overlooked or ignored until tree or shrub directly to leaves. They spend most of the summer feeding
branches “mysteriously” start to die. Upon closer examina- on leaves and excreting honeydew. They return to the
tion, these branches are likely to be covered with small twigs and bark where they spend the winter as settled
bumps that are actually scale insects. They damage plants second stage scales. They continue to grow on twigs in
by sucking out plant juices. the spring until winged males mate with wingless females,
From a damage standpoint, there are two types of who swell with up to 1,000 eggs.
scales, those that excrete a sugary liquid (honeydew), and
those which do not. Honeydew is both a nuisance and a CONTROL MEASURES
threat to plant health. Parked cars, walks, and benches Inspection
beneath infested trees often become a sticky mess. The Check plants for live scale infestations. Flip over
sugary liquid attracts ants, flies and wasps. Plants become suspicious looking bumps on twigs and branches with a
unsightly when this liquid becomes a food for a black thumbnail. Bark is usually intact beneath a scale. When a
fungus called sooty mold. This mold can shade leaves soft body is beneath a cover, the plant is likely to have live
and reduce plant growth. armored scales. When the bump itself can be squashed
Soft (Lecanium), kermes, and bark scales produce it is likely to be some other type of scale. When honeydew
honeydew. These scales feed directly on plant parts that falls from a tree, leaves should be inspected for live soft
transport fluid and nutrients. Armored scales and pit scales or mealybugs.
scales do not produce honeydew. The armored scale's
straw-like mouth moves like a plumber’s snake to burst Cultural Control
plant cells and feed on their contents. Pit scales are likely Scales will thrive on trees that are under stress. Plant
to do the same to the raised plant tissue that surrounds trees that are correctly suited to your landscape site.
them. Slower growing plants with variegated leaves can require
more care. Keep them watered. Carefully inspect newly
GENERAL SCALE LIFE CYCLE purchased plants for scales. If a twig is unusually bumpy
Scales spend most of their lives feeding on the same and leaves are somewhat yellowed it may have scales.
spot of a plant, and unable to walk. After the eggs hatch If a plant is normally a rapid grower, such as red-osier
beneath females the young scales are called crawlers dogwood, or wintercreeper euonymus, consider cutting
because they can walk at this time. Crawlers are small out heavily infested branches with a pruning shears to
(<1/32”) and flattened, looking like dust on the plant sur- foster growth of uninfested shoots.
face. Scale infestations spread when crawlers walk or are
blown by the wind to nearby plants or plant parts. Biological Control
After an armored scale crawler begins to feed, it be- The stationary life of scales makes them easy targets
comes very flat and covered with a clear wax shell. As it for many natural enemies including lady beetles and mi-
continues to grow, it remains beneath its waxy armor. This croscopic wasps. These beneficial insects can keep the
armor is difficult to penetrate with insecticides. Winged numbers of scales quite low in a natural woodland setting.
males crawl out from beneath their cover and mate with For more on biological control please visit <http://www.
covered females who produce eggs. Females can produce cips.msu.edu/hcr125/GuideScales.htm>.
about 100 eggs each.

PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, IN 47907

http://www.entm.purdue.edu/Entomology/ext/targets/e-series/e-list.htm
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Chemical Control kill scales after they have settled while the scale body is
Conventional pesticides cannot penetrate a scale’s still somewhat clear. After it dries, it is not toxic to natural
tough skin or waxy cover. Scale crawlers are killed by enemies that can fly back to an infested plant and feed
these pesticides when they are covered during foliar on the remaining scales. When applied in winter at the
application, or as they walk along treated surfaces. To dormant rate, horticultural oil kills scales that do not
achieve maximum kill, pesticides in this group should be winter as eggs beneath the scale cover (See Table 1 for
sprayed at the begining of the crawler period. Several winter stage).
obstacles make conventional materials undesirable for For persistent scale problems or those scales that
managing scales. Thorough coverage on tall trees is winter in the egg stage (pine needle or oystershell scle)
difficult and these materials do not kill scales after they insect growth regulators can be a promising biorational
settle. More importantly, these materials kill the scale’s alternative. Apply when scales are crawling or when the
natural enemies responsible for lasting control in the scales are still clear. These materials (e.g., Pyriproxifen)
landscape. Soil-applied systemic insecticides may have kill insects as they molt.
less of an impact on natural enemies but some are only To get the most from both natural enemies and pes-
effective on scales feeding on leaves, or those that are ticides, do the following:
actively producing honeydew. 1. Identify the scale. Use picture sheet and Table 1.
Conserve scale natural enemies and kill scales on 2. Inspect plants for live scales in early spring and for
infested trees by using a biorational material like horti- active crawlers in summer.
cultural oil. This material works by smothering scales. 3. Use Table 2 to make decisions about pesticide use,
Unlike other conventional pesticides, this material can and Table 3 to select a pesticide.

Table 1. Most Common Scales of Indiana

Approx. Crawler
Plants Most Seriously Activity
Photo of Insect Kind and Description of a Scale Affected (Winter Stage)
SCALES THAT DO NOT PRODUCE HONEYDEW
Armored scales with dark covers:
Obscure Scale (Melanaspis obscura): Small Pin-oaks, and red oaks, espe- July
(1/16"), round gray scales. Twigs appear covered cially in urban areas (immature)
with silver shells when rubbed. Black central
nipple.

Oystershell Scale (Lepidosaphes ulmi): Small Lilac, birch, dogwood, ash, elm, May and July
(1/8" long) gray or brown scales shaped like oys- poplar, soft maple, privet, wil- (eggs)
ter shells. May completely encrust branches. low, walnut, hemlock

San Jose Scale (Quadraspidiatus perniciousus): Flowering ornamental fruit Mid-June to mid-July
Tiny (1/16") gray circular scales about the size of trees, rose, quince, mountain (immature)
a pinhead and having a yellow central nipple. ash, pyrancantha, and others
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Table 1. Most Common Scales of Indiana

Approx. Crawler
Plants Most Seriously Activity
Photo of Insect Kind and Description of a Scale Affected (Winter Stage)
Winged Euonymus Scale (Lepidosaphes yanan- Burning bush (Euonymus May, July, September
gicola): Small oystershell shaped (1/16") covers alatus) (eggs)
found along ridges of winged euonymus branches
(Burning bush). Much thinner than oystershell
scale.

Armored Scales with white covers:

Euonymus Scale (Unaspis euonymi): Elongated Euonymus, pachysandra, bit- Late May to early
(1/16") white ridged scale covers of males on tersweet June, late July to
leaves. Females on stems resemble oystershells August
but are more flattened. (adult female)

Pine Needle Scale (Chionaspis pinifoliae and Pines, fir, spruce May, July
C. heterophyllae): Small elongated (1/8") white (eggs)
scales attached to needles of overgreens. C. June
heterophyllae feed on pine only, while C. pinifolae (adult female)
feed on other conifers as well. Can winter as egg,
or adult female.

Scurfy Scale (Chionaspis furfura): Small elon- Young elms, apple, willow, May, July
gate (1/10"), dirty white, pear shaped scales. Lie dogwood (adult female)
flat on bark. Purplish-red crawlers.

Juniper Scale (Carulaspis juniperi): Tiny (1/16") Juniper and arborvitae May, July
circular grayish-white scales with a yellow cen- (adult female)
ter. Packed between leaf scales of Juniper and
arborvitae.
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Table 1. Most Common Scales of Indiana

Approx. Crawler
Plants Most Seriously Activity
Photo of Insect Kind and Description of a Scale Affected (Winter Stage)
Pit Scales (Pit shaped bumps on twigs): Oaks, especially pyramidal June
Golden Oak Scale (Asterolecanium variolosum): English oak (adult)
This scale makes a circular pit (1/8") around its
gold colored body. Edge of body is surrounded by
a waxy fringe.

SCALES THAT PRODUCE HONEYDEW

Cottony Maple Scale (Pulvinaria innumerabi- Soft maple, boxelder, linden June
lis) (soft scale): Large (3/8") scales attached to (adult)
undersides of branches. In spring, when deposit-
ing eggs, scales on twigs resemble strings of
popcorn. Crawlers are found on the undersides of
branches.

European Elm Scale (Gossyparia spuria) (bark Elms of all ages Mid-May to mid-June
scale): Oval shaped (1/4"), reddish brown scales (immature)
surrounded by a white waxy fringe. Found on
bark, often in the crotch of small banches.

Fletcher's Scale (Parthenolecanium fletcheri) Yew (Taxus) Mid-June to mid-July

- Formerly Taxus Lecanium (soft scale). Round (immature)
(3/8") deep brown scales found on yews.

Magnolia Scale (Neolecanium cornuparvum) Magnolia only September

(soft scale): Large female up to 1/2 inch long. Skin (crawler)
is covered with white waxy powder.
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Table 1. Most Common Scales of Indiana

Approx. Crawler
Plants Most Seriously Activity
Photo of Insect Kind and Description of a Scale Affected (Winter Stage)
Pine Tortoise Scale (Toumeyella parvicornus) Pines only Mid-June to mid-July
(soft scale): Deep brown to black scales (3/8") (adult female)
with light colored spots in a pattern that gives
them a turtle like appearance. If cream colored
stripes are present, then it is the Striped Pine
Scale (T. pini). Life cycle of T.pini is poorly under-
stood.

Spruce Bud Scale (Physokermes hemicryphus): Spruce June

Brown adult females (1/4") closely resemble (immatures on under-
spruce buds late in the season. Black crawlers. side of needles)

Tuliptree Scale (Toumeyella liriodendri) (soft Tuliptree, poplar, magnolia, September (crawler)
scale): Females up to 3/8" long with orange ridges walnut, linden
on a brown body. Black crawlers.

SCALE RELATIVES
Hawthorn Mealybug (Phenacoccus dearnessi): Hawthorn May-June
All stages covered with white waxy filaments. (immature)
Adults up to 3/16" and all stages are mobile. Black
crawlers.

Oak Kermes Oaks September

Pubescent Leaf Kermes (Nanokermes pubes- (immature)
cens)
Pin Oak Kermes (Allokermes galliformis): Adults
of both species are up to 3/8" long and are often
present near terminal buds.
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Table 2. Assessing the Scale Infestation1

Situation Response Comment

Live scales on plant in spring when plant is dormant. Dormant season spray Low impact on natural enemies
Live armored or pit scales on plant. Crawlers are present Summer biorational spray Low to moderate impace on natural en-
or have recently settled. Some new leaf discolor or branch emies. Some parasitic wasps active at this
dieback. time.
OR
Live honeydew producing scales on plant. Crawlers are pres- Wash honeydew from cars, benches, and
ent or have recently settled. Some new leaf discolar or branch patios to manage honeydew nuisance.
dieback.
Live armored or pit scales on plant. Crawlers are present or Summer conventional spray High impact on natural enemies. Do not
have recently settled. New leaf discolor or branch dieback is use in combination with summer systemic
severe. spray.
OR
Live honeydew producing scales on plant. Crawlers are
present or have recently settled. New leaf discolor or branch
dieback is severe.
Live honeydew producing scales on plant. Scales are feeding Summer foliar systemic High impact on natural enemies. Most
on leaves. New leaf discolor or branch dieback is severe. spray or systemic soil effective soon after crawlers arrive on
insecticide leaves. Soil applied systemic kills all feed-
ing stages of honeydew producers, or stem
feeding scales.
1
Always conserve natural enemies when plant health and customer satisfaction can be maintained.

Table 3. Chemical Responses to Scale Infestations

Use in 100
Response Insecticide Use in 1 Gal. Gal. Comment
Dormant season sprays Superior Oil (Sunspray, Volk 2.5 oz. or 5 Tbsp. 3 gal. Use before spring growth whtn temperature is above
Oil, Clean Crop, Scalecide, 40°F. Do not follow with Captan, Pyrene, Karathane,
and others) or Morestan, Sevin, or Cygon for 1 month. Use ultra-
fine oil at low rate for soft maples. Can temporarily
Ultra-fine Oil (Ultra-Fine, 4-5 oz. or 8-10 Tbsp. 3-4 gal. remove "bloom" from blue-needled conifers.
Sunspray 6E Plus, Rock-
land, and others)
Summer biorational Ultra-fine oil (Ultra-Fine, 2.5 oz. or 5 Tbsp. 2 gal. Can temporarily remove "bloom" from blue-needled
spray (soon after crawl- Sunspray 6E Plus, Rock- conifers. Drought stressed plants, dwarf Alberta
ers settle, while they still land and others) spruce and soft maples can be sensitive. Do not fol-
appear clear) low with compounds as listed above. Avoid spraying
OR on wet foliage.

Pyriproxifen (Distance 1-1.5 cups Professional use only. Do not use more than twice a
season. Does not kill adults.
Summer conventional deltamethrin (Suspend SC) 3/4 - 1.5 tsp. 4-8 oz. For licensed applicators only
spray (when crawlers are
active) malathion (Malathion 57EC) 4 tsp. 2 pts. Injury may ocur on hickory, virburnum, lantana and elm
OR
acephate (Orthene 75S) 2 tsp. 10 oz. May injure some crabapples and virburnums
OR
lambda-cyhalothrin (Battle - 1.5-5 fl. oz. For licensed applicators only
WP, Scimitar WP)
OR
bifenthrin (Talstar 10WP) 2 tsp. 2 1/4 cup For licensed applicators only
OR
cyfluthrin (Tempo, Decatha- See label See label For licensed applicators only
lon)

cyfluthrin (Bayer Lawn & 2 Tbsp. - Homeowner use

Garden)
Summer systemic spray acephate (Orthene 75S) 2 tsp 10 oz. Foliar spray.

imidacloprid (Merit 75WSP) See label See label Apply to soil according to label 3 weeks before crawl-
(Bayer tree & shrub insect ers emerge
control)
READ AND FOLLOW ALL LABEL INSTRUCTIONS. THIS INCLUDES DIRECTIONS FOR USE, PRECAUTIONARY STATEMENTS (HAZARDS TO HUMANS, DOMESTIC ANIMALS, AND
ENDANGERED SPECIES), ENVIRONMENTAL HAZARDS, RATES OF APPLICATION, NUMBER OF APPLICATIONS, REENTRY INTERVALS, HARVEST RESTRICTIONS, STORAGE AND
DISPOSAL, AND ANY SPECIFIC WARNINGS AND/OR PRECAUTIONS FOR SAFE HANDLING OF THE PESTICIDE.
Revised 7/2005
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