Scale Insects On Ornamentals

EB1552E

Daniel A. Suomi

Scale insects are common on ornamental trees andshrubs. Occasionally they build up in large enough numbersto cause serious damage or death to the host tree. Scalesdo not resemble typical insect pests, so they often gounnoticed until a large population has developed andcaused damage. To prevent damage from scale insects,maintain healthy, vigorously growing trees, monitorinsect populations, and use correct control measureswhen those populations increase.

Ornamentals, by definition, do not bear edible fruits,nuts, or berries. Chemicals labeled for use on ornamentalsdo not necessarily allow use on bearing plants. Alwayscheck the label and follow directions closely.

Hosts and DamageScale insects attack many types of trees and shrubs,

garden plants, and houseplants. Considerable damagecan occur when large numbers of these insects feedupon plants already weakened by environmentalstresses, such as drought, or disease. The scale removesplant juices with piercing-sucking mouthparts. At times,certain scale insects produce large amounts of honey-dew (an excess of liquid and sugar expelled from theirbodies). This sticky material can serve as a growth

Figure 1. Sooty Mold Fungus on Needles 1

medium for a sooty mold fungus (Figure 1). Duringtimes of high populations, some scales become soabundant that an infested portion is totally encrustedwith insects (Figures 2 and 3).

Life CycleScale insects have three distinct life stages (egg,

immature, adult), and several complete generationsmay occur in a single year. Eggs are produced by adultfemales beneath the scale covering or in a cottonymaterial, and in many cases, the cold winter monthsare passed in this stage. Tiny, six-legged crawlers(Figure 4) emerge from the eggs, move to newergrowth on the plant, insert their mouthparts, andbegin to feed. A scale-like covering produced fromwaxy filaments and feces then forms over eachindividual. Scale species are identified by the color andshape of the covering. The covering protects scales frompredation by other insects and from insecticides. Themale scale is often a slightly different shape than thefemale and passes through a tiny, winged stage(Figure 5). Casual observers seldom see this wingedstage. Females are wingless and usually remain in oneplace after inserting their mouthparts into plant tissues.

Figure 2. Scale Insects on Apple2

Figure 3. Oystershell Scale Encrusted Tree Bark 3

MonitoringA crucial step in scale control is determining when

the crawlers emerge. A hand lens or magnifying glasswill help you discover when this occurs. Apply double-sided sticky tape near adult scales to trap crawlers asthey migrate to new growth. For convenience, you mayput an infested branch in water to keep it from dryingout, and leave it outdoors in a shady place. Observe thescale eggs every few days for a hatch. You should begina control program when the crawlers appear. When youconsult the life history charts for different scale species,remember that emergence times will vary dependingon your location and seasonal weather conditions.

ControlYou can control scales in several ways. Apply dormant

(or delayed dormant) oils; they work by cutting off theinsect's oxygen supply (see PNW328 for more infor-mation). Use these oils when plants are not activelygrowing (late winter to early spring). Using too muchoil may cause burning or other damage to plants. Oilsmust be applied when temperatures are greater than40°F to prevent separation of oil and water. Apply a light,superior oil-insecticide mixture just as plants begin togrow to control emerging crawlers. This time period

usually lasts only a few days—timing is critical. The oilmust be applied before leaves open, yet late enoughso that this mixture will kill the crawlers.

The best time to apply any insecticide is when crawlersare present. These tiny insects do not have a protectivecovering and are vulnerable to almost any chemicalregistered for this use. Cyfluthrin, malathion, acephate(Orthene), or insecticidal soap are all registered forcrawler control. Cover the plant thoroughly to kill thecrawlers with one application. Read the label and usethese insecticides when bee activity is limited. Systemicinsecticides (such as Orthene) applied as a foliar sprayor incorporated into the soil, can help control adultscale insects during the growing season. Each situationis unique; it is important to know which scale speciesis present. Read chemical labels to determine if anyrestrictions apply to your particular situation and becertain the plant you intend to spray is indicated onthe label.

Systemics vs. Contact InsecticidesUse systemic insecticides to control insects that feed

with piercing-sucking mouthparts inserted into planttissues. Apply the materials either as a foliar spray, wherethe insecticide concentrates in leaves, or as a root

4 Figure 4. Crawlers Emerging from Beneath Adult Scale Covering

drench, where the plant's water-conductive tissue,known as xylem, transports the material to theleaves from the roots. Scale insects found on barkfeed in the food transport tissue, called phloem,and do not feed on xylem tissue. Therefore,phloem feeders are not killed by systemics. Theexception to this occurs if an insecticide has bothcontact and systemic activity (e.g., Orthene) andis applied when the scale is vulnerable to contactpesticides. Thorough coverage is important whenusing contact insecticides since many crawlers feedon the undersides of leaves and on twigs, branches,or trunk. Scale insects feeding on leaves will bekilled by systemics, as these concentrate in leaftissue whether they are applied as direct sprays oras a root drench.

The following pages describe several major scalespecies in the Pacific Northwest. Use the photo-graphs to identify the scale insect infesting theplant(s), then determine if beneficial insects (e.g.,ladybird beetles or lacewings) are active. Thesebeneficials often will reduce scale infestations tolevels where no other controls are necessary.

If no beneficials are present and scales occur inlarge numbers, select an insecticide appropriate for

that species. Consult the chart for the best timeto apply materials. Examine the site or situation care-fully. Avoid applying insecticides in places wherethey could injure animals, such as bodies of water,vegetable gardens, or near pet food dishes.

Scale CategoriesTYPE I scales feed on foliage.TYPE II scales feed through the bark of

branches and trunk.

5

Figure 5. Male Scale Insect

Juniper ScaleCarulaspis juniperiHosts: arborvitae, chamaecyparis, cypress, juniper, redcedarDamage: loss of green luster, leaves turn dull green orbrown, no new growth on infested foliageDescription: TYPE I scale, female 1/16" in diameter,round, off-white with a central yellow dot; brightyellow crawlers migrate to newer growth to feed.Overwintering Stage: adult scales on leavesOther Factors: one female scale produces up to 40eggs under the covering; scale and crawlers can bemoved between hosts by animals or humans.Control: dormant oil in late March to early April;malathion 50% emulsifiable concentrate (EC), insecti-cidal soap, or cyfluthrin 0.75% EC when crawlersemerge; oils may cause discol-oration on certain junipers;if in doubt, test a smallarea before using oil onthe entire plant.

6

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Adult

Pine Needle ScaleChionaspis pinifoliaeHosts: all species of pine and occasionally Douglas-fir,spruce, cedarDamage: weakens and slows growth, foliage becomesyellowish; in heavy infestations foliage appears white.Description: TYPE I scale, female 1/8" long, pear-shaped, white, waxy; reddish crawlers.Overwintering Stage: eggs under female scalecoveringOther Factors: one generation per year (possibly twoin western Washington, second generation nymphsappear in July); each female produces up to 100 eggs;nymphs dispersed by wind; this species is a problemespecially along dusty roads and on stressed trees.Control: dormant oil in spring before plant growthbegins; malathion 50% EC,insecticidal soap, orcyfluthrin 0.75% ECfor crawler control.

7

Egg

Crawler

Adult

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Lecanium scaleParthenolecanium spp.Hosts: alder, arborvitae, blueberry, dogwood, elm,hawthorn, maple, linden, poplar, raspberry, rhododen-dron, willow, yew, most fruit trees, and many other plantsDamage: plant loses vigor, leaves are smaller or do not form.Description: TYPE I (overwintering and mature) andTYPE II (crawler) scale, 1/8"–3/16" long, typicallyshiny brown, turtle-shaped, clusters in large numberson small branches at leaf axils, nodes, or fruit spurs.Overwintering Stage: immature scales on branchesOther Factors: one of the most frequently encounteredspecies; a single generation each year; the immature scales,unlike most others, remain mobile throughout their life;subject to rapid increases and declines in populations.Control: many predators and parasitoids attackLecanium scale, chemical control often is unnecessary;dormant oil in late winterto early spring; immaturescale control fromJune–September usingcyfluthrin 0.75% EC,Orthene 9.4% EC, orinsecticidal soap.

8

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

Oystershell ScaleLepidosaphes ulmiHosts: over 400 broadleaf trees (including ash, maple,poplar, willow), shrubs, herbaceous plants, and fruit trees(especially apple)Damage: weakens, and if abundant and not controlled,will kill large portions of the plant.Description: TYPE II scale, 1/8" long, generally brownto ashy gray, resembling tiny oystershells; yellowish crawlerspass through a “white cap” stage; new infestations arepinkish in July–August, while old scales are gray or black.Overwintering Stage: as eggs under the female scale cover-ing; highly resistant to dormant applications of insecticidesOther Factors: probably the most readily recognizedscale as large numbers often found massed togetherencrusting bark of trunk and branches.Control: numerous predators and parasites attack thisscale, but are usually ineffective;malathion 50% EC, cyfluthrin0.75% EC, or Orthene 9.4%EC for crawler control; spraywhen crawlers first emergeand about 10 days later tokill those still emergingfrom eggs.

9

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

San Jose ScaleQuadraspidiotus perniciosusHosts: alder, apple, birch, cherry, cotoneaster, elm, maple,peach, pear, poplar, willow, and many other deciduoustrees and shrubs, especially damaging to fruit treesDamage: found on twigs, branches, leaves, and fruit,often killing the infested portion of the tree, reddishspots appear where the scales are feeding; bark appearsshaggy or rough.Description: TYPE I and II scale, 1/16" in diameter, femalescale gray with a central, yellow dot; crawlers are yellow.Overwintering Stage: as black-colored immature scaleson bark, very susceptible to dormant applications ofinsecticides.Other Factors: very common and destructive scale;crawlers can be moved by wind, birds, or humans.Control: predators will help keep small scale populationsin check, but when largenumbers of scales arepresent, chemical controlis necessary; use a dor-mant oil to suffocateoverwintering forms;cyfluthrin 0.75% EC orinsecticidal soap forcrawler control.

10

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Nymph

Adult

Spruce Bud ScalePhysokermes piceaeHosts: spruce (certain pines also have been recordedas hosts)Damage: found especially on lower branches of spruce,young feed on needles, adults feed on small branches;abundant honeydew produced.Description: TYPE I and II scale, 1/8" in diameter,mature scales reddish brown and globular, found inclusters of three to eight at the base of new twig growth;crawlers are olive brown.Overwintering Stage: young scales on the undersideof needlesOther Factors: these scales so closely resemble sprucebuds that they often are overlooked; excessive honeydewproduction leads to growth of black sooty mold thatgives the tree an unhealthy appearance, honeydewattracts many bees, wasps, andants.Control: delayed dormantoil in spring (Coloradoblue spruce will discolorwhen oil is used); Orthene9.4% EC, or insecticidalsoap for crawler control.

11

Egg

Crawler

Nymph

Adult

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Cottony Maple ScalePulvinaria innumerabilisHosts: primarily maple, but will attack many ornamentalsincluding alder, apple, dogwood, elm, lilac, pear, poplar, andwillowDamage: withdrawal of sap causes dieback of twigs andbranches, and in large infestations, causes tree death;honeydew and sooty mold accompany large populations.Description: TYPE I and II scale, fully developed scale 1/4"long, dark; flattened scale produces large white, cottony eggsac; crawlers are green-yellow.Overwintering Stage: as immature scales on twigs andbranches, this stage is susceptible to dormant insecticidalapplications.Other Factors: one of the largest scale insects on ornamentals;females can produce up to 1,000 eggs; crawlers feed on leavesthroughout the summer and move back to twigs in the fall.Control: many predators andparasites attack cottony maplescale and often reducepopulation numbers tolevels that will not dam-age the tree; dormant oilin late winter before treegrowth begins; Orthene9.4% EC, or insecticidal soapfor crawlers on leaves.

12

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

13

Brown Soft ScaleCoccus hesperidumHosts: camellia, dogwood, daphne, holly, but especiallya pest of greenhouse ornamentals and houseplantsDamage: build up in large numbers on leaves and maykill the host plant; produce abundant honeydew.Description: TYPE I scale, 1/8"–3/16" in length, oval,flattened, soft shell, green-brown in color; crawlersyellow-brownOverwintering Stage: as immature scales on leavesOther Factors: these scales feed on leaf undersurfaceand often are overlooked; primarily a pest of indoorornamentals; two generations per year outside, up tosix generations indoors.Control: numerous predators and parasites controlthese insects in ornamentals outdoors, predators canoffer relief from scale infestations if introduced intogreenhouse settings; cyfluthrin0.75% EC can be appliedto control adult scales,but thorough coverageis necessary; Orthene9.4% EC or insecticidalsoap for crawler control.

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Nymph

Adult

European Elm ScaleGossyparia spuriaHosts: elmDamage: causes premature yellowing and loss of leaves,then twigs and branches die back, small trees may bekilled; abundant honeydew produced.Description: TYPE I and II scale, 1/8" long, reddishbrown with a conspicuous fringe of white cottony wax;crawlers are brown.Overwintering Stage: as immature scales in cracks ofbark on small branches and branch crotches, susceptibleto dormant insecticide applications.Other Factors: immature forms resemble mealybugs;this insect can cause extensive damage to elms.Control: apply dormant oil to twigs and branchesbefore buds swell in spring; for crawler control, applyOrthene 9.4% EC (only for Siberian and Chinese elm),cyfluthrin 0.75% EC, orinsecticidal soap.

14

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

15

Azalea Bark ScaleEriococcus azaleaeHosts: andromeda, azalea, blueberry, hawthorn,rhododendron, willowDamage: found on the bark of twigs and stems; whenlarge numbers are present, plant becomes yellow,stunted, or weakened; abundant honeydew on whichsooty mold thrives.Description: TYPE II scale, adult female is red, 1/16"long, round, and covered by a white, waxy sac; crawlersare red.Overwintering Stage: as partially developed nymphson barkOther Factors: usually one generation per year, but haspotential for two in the southern part of Washington.Control: this scale often is heavily parasitized; whenchemical control is necessary, apply cyfluthrin 0.75%EC, malathion 50% EC,or Orthene 9.4% EC tobranches for crawlercontrol.

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

Cottony Camellia (Taxus) ScalePulvinaria flocciferaHosts: camellia, English ivy, holly, hydrangea, maple,rhododendron, yewDamage: causes off-colored or light green foliage;weakens plant over time; honeydew and sooty moldbecome abundant.Description: TYPE I scale, mature form light brownto yellow, oval, 1/8" long, after laying eggs, female scalehas a white sac attached, in time the brown coveringdisappears leaving only the egg sac attached to plantsurfaces; egg sacs are 1/4" long and may contain up to1,000 eggs; light yellowish tan crawlers.Overwintering Stage: as immature nymphs, usuallyon twigs and leavesOther Factors: eggs hatch in early summer in mostparts of its range.Control: apply Orthene9.4% EC, malathion 50%EC, or insecticidal soapfor crawler control.

16

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

17

Hemlock ScaleAbgrallaspis ithacaeHosts: spruce, hemlockDamage: particularly in Colorado blue spruce, the treeloses vigor and sheds large numbers of needles, creatingextensive bare areas, severe infestations result in deathof host.Description: TYPE I scale, 1/16" in diameter, oblong toelliptical, female scale brown to gray with a prominent,central dot; crawlers are green to yellow.Overwintering Stage: as dark brown to dark grayimmature scales on needles, susceptible to dormantapplications of insecticides or oilsOther Factors: very common and destructive in centralWashington on spruce, especially Colorado blue spruce,most common on trees under stress.Control: predators are not effective in reducing popu-lations; control with dormantoil sprays just before budbreak (be cautious ofneedle discoloration onblue spruce); cyfluthrin0.75% EC, malathion50% EC, or insecticidalsoap for crawler control.

DEC JANFEB

MA

RA

PR

M

AYJUNJULAUG

SE

PO

CT

N

OV

Egg

Crawler

Nymph

Adult

Daniel A. Suomi, former entomologist at WashingtonState University, Pullman, furnished the photographsfor pages 2, 3, 4, 20, and back cover. Roger D. Akre,Washington State University entomologist (deceased),provided the photographs for page 1 (sooty mold),page 6 (juniper scale) and page 14 (European elmscale). Photographs on pages 11 and 15 provided byArt Antonelli, Extension Entomologist, WSU.Front cover photograph by Brandon Burch, © 1990.

Use pesticides with care. Apply them only to plants,animals, or sites listed on the label. When mixing andapplying pesticides, follow all label precautions toprotect yourself and others around you. It is a violationof the law to disregard label directions. If pesticides arespilled on skin or clothing, remove clothing and washskin thoroughly. Store pesticides in their originalcontainers and keep them out of the reach of children,pets, and livestock.

College of Agricultural, Human, and Natural ResourceSciences

Issued by Washington State University Extension andthe U.S. Department of Agriculture in furtherance ofthe Acts of May 8 and June 30, 1914. Extension pro-grams and policies are consistent with federal and statelaws and regulations on nondiscrimination regardingrace, sex, religion, age, color, creed, national or ethnicorigin; physical, mental or sensory disability; maritalstatus, sexual orientation, and status as a Vietnam-eraor disabled veteran. Evidence of noncompliance maybe reported through your local Extension office. Tradenames have been used to simplify information; noendorsement is intended. Revised May 1996. Slightlyrevised by Art Antonelli, June 2006. Subject codes255, 352. EB1552