Hugh Smith and Richard Cowles
Connecticut Agricultural Experiment Station
Valley Laboratory
153 Cook Hill Road
Windsor, CT 06095
860-683-4977
Hugh.Smith@ct.gov
Richard.Cowles@ct.gov
Rose Hiskes

Scale Insect Pests of Connecticut Trees and Ornamentals

Scale insects are among the most difficult pests of woody ornamentals to manage.  There are several types of scale insect, although the most common scale pests for Connecticut growers are armored scales (Diaspididae), soft scales (Coccidae) and mealybugs (Pseudococcidae).  Armored scales tend to be smaller (2-3 mm) than soft scales (5-10 mm) and often appear as though they are part of the plant, making them difficult to detect. Armored scales secrete a hard covering that helps protect them from insecticides and natural enemies, and prevents them from drying out.  This covering can be pried away from the scale body with the tip of a blade or an insect pin.  Common armored scale pests in Connecticut include elongate hemlock scale on hemlock and fir trees, white prunicola scale on many hosts including almond, cherry, lilac and privet, and euonymus scale on euonymus, privet and other hosts.  Soft scales produce a hard layer of wax on their outermost skin that provides protection.  Unlike armored scales, this outer covering cannot easily be removed from soft scales.  Common soft scale pests in Connecticut include the cottony camellia scale on holly, yew and euonymus, Fletcher scale on arbor-vitae and yew, and tuliptree scale on linden, magnolia and other hosts.   Mealybugs are covered with cottony waxy filaments.  Common mealy bug pests of Connecticut ornamentals include the taxus mealybug on yew, and the apple mealybug and the Comstock mealybug, both of which attack many hosts.  Common scale pests of Connecticut and their hosts are presented in Table 1. 

Life cycle 
Depending on the species, scale insects can overwinter as eggs, immatures, or adults.  Females lay eggs beneath the scale covering or in a cottony mass.  Some scale species have one generation per year; some species have a few or several generations per year.  First stage immatures, called crawlers, emerge from eggs in spring and move to a feeding site.  Crawler emergence usually lasts 2-4 weeks.  For species with multiple generations per year, there are repeated emergences in the warmer weather.  Once scale crawlers settle to feed, they become immobile.  When the crawler molts into the second stage immature, it begins to produce the protective scale covering.  Mealybugs are distinct from most other types of scale insect in that they remain mobile throughout their development.  Adult male scales and mealybugs are delicate fly-like creatures that live a short time and are rarely observed. 

Damage
Even low density scale and mealybug infestations cause aesthetic damage and can make plants unmarketable. Scale insects have piercing-sucking, straw-like mouthparts which they use to feed on plant fluids.  Heavy infestations can debilitate plants, causing yellowing of leaves, leaf die-back and death of the plant.  Soft scales and mealybugs can produce copious amounts of honeydew, a sugar-rich excretion which makes plants sticky and serves as a substrate for sooty mold.  In extreme cases, the sooty mold interferes with photosynthesis and trees shed the blackened leaves.  Ants are attracted to honeydew, on which they feed.  Certain ant species will tend and protect colonies of scales in order to make use of the honeydew. Because ants will move scales from infested to uninfested plants, and will protect scales from their natural enemies, the first step in managing honeydew-producing scales is to eliminate their associated ants. Armored scales are often associated with decline or dieback of their hosts, which may be triggered by their injection of toxic saliva while feeding. The beech scale causes long-term changes in the bark which leads to eventual fungal infection causing an often-lethal canker.   

Monitoring
Incipient scale infestations can be monitored by visual inspection of the plant.  Depending on the host and the behavior of the scale species, scales can be found in bark crevices, twig crotches, leaf veins or other locations on the plant.  Black electrical tape can be placed around twigs or branches near a scale infestation in order to track the emergence of crawlers.  Wrap the tape with the sticky side facing in and double back to expose the adhesive on the outer surface, then double the tape over on itself one last time to leave a small handle to permit unwrapping the trap to observe the trapped insects.  Crawlers will appear on tape as yellowish, flattened insects about the size of a period on printed text.   Beating foliage by hand onto a light-colored surface will dislodge crawlers and make them easier to detect.  Plants and crawler traps should be checked at least once a week.  A hand lens is useful for observing crawlers. 

When scouting for scales insects it is important to look for evidence of natural enemies. Scales have many naturally-occurring enemies, including predators such as ladybird beetles and lacewings, and tiny parasitic wasps that lay eggs inside the scale.  Ragged remnants of scales are good evidence of predation, while neat circular holes in the scale are evidence that a parasitoid emerged.  While parasitic wasps are not often observed, it is not unusual to see ladybird beetles and other predators associated with scale infestations.  Beating samples are useful for finding scale predators, parasites, and even scale crawlers. If scouting reveals the activity of natural enemies on scales, it is advisable to delay the application of insecticides, and to continue monitoring to determine if natural enemies will suppress the infestation.  Options most compatible with integrating biological and chemical control of scales are (1) to apply a root- or trunk-absorbed systemic insecticide to limit the insecticide exposure of the beneficials, or (2) to apply a selective, insect growth regulator class of insecticide registered for control of scales (see below).  

Management
Cryptolaemus montrouzieri and Lindorus lophanthae are species of ladybird beetle that are commercially available for the suppression of soft scales and mealybugs.  Naturally-occurring and naturalized species of Chilocorus ladybird beetles will attack armored and other scale insects.  Parasitic wasps are also available commercially for suppression of scales.  However, naturally occurring populations of parasites usually will colonize sizable scale populations without having to make artificial releases.  Under favorable conditions, natural enemies can help keep scale populations below economically-damaging levels.  Natural enemies purchased from commercial suppliers tend to work best in enclosed environments, such as greenhouses, and when pest populations are low.  Natural enemies are easily decimated by many commonly used insecticides.  Broad spectrum insecticides such as acephate, bifenthrin, carbaryl, chlorpyrifos, cyfluthrin, dimethoate and malathion are not compatible with an integrated approach to managing scales or other arthropod pests.  Low density scale infestations that are being kept in check by natural enemies can flare out of control if insecticides are used inappropriately. 

The crawler stage is most susceptible to insecticides because it lacks a well-developed protective scale cover.  Furthermore, the mobility of crawlers can bring them into contact with insecticide residues on plant surfaces.  For this reason it is crucial to time insecticide applications with crawler emergence and activity.  Dormant stage horticultural oils are used to suffocate all stage of scale insect, and are typically applied in the late winter or early spring when plants are not actively growing.  Dormant oils may discolor some species of evergreen tree, and should only be applied when temperatures are above 40° F (4.4° C).  A partial list of insecticides that can be used in Connecticut to manage scale insects is presented in Table 2. 

Properties of insecticides registered for managing scales
The contact insecticides, horticultural oil and insecticidal soap, are only effective when they thoroughly wet the surface of the scale insect.  While horticultural oil will kill through suffocation any stage of scale that is adequately covered, insecticidal soap may only be effective against those scales that are less protected by a well-developed scale cover.  Some armored scales are not adequately controlled with horticultural oil, possibly because there may be an air gap between the scale cover and the live insect, which would protect it from suffocation. 

Residual broad-spectrum insecticides (carbaryl, chlorpyrifos, and malathion) are generally not compatible with integrated management of scale or mealy bug populations, although they may be effective on their own.  The very long residual pyrethroids, bifenthrin, lambda-cyhalothrin, and cyfluthrin are of special value because one thorough spray can disrupt a season of crawler activity.  Cyfluthrin is especially disruptive to IPM programs because it kills spider mite predators while not being toxic to mites; as a result, use of this product by itself or in a mixture with imidacloprid is likely to cause rust mite and spider mite outbreaks. 

Systemic organophosphate insecticides (acephate and dimethoate) have been supplanted by the neonicotinoid class of insecticides (acetamiprid, clothianidin, dinotefuran, imidacloprid and thiamethoxam).  The organophosphates are much more toxic to the applicator, birds, and fish, and so the U.S. EPA has been gradually limiting their use.  The neonicotinoids can be subdivided into two categories, based upon their degree of systematicity.  Imidacloprid, clothianidin and thiamethoxam have limited mobility in plants, and should only be used to target those species of scales (and other sucking insects) that produce honeydew.  Acetamiprid and dinotefuran have much greater solubility, and so they can be used to target armored scales.  Dinotefuran has an unusual property allowing it to penetrate bark following a bark spray and be translocated to the feeding site of armored scales; it is especially useful for targeting scales feeding in hidden locations on plants (such as Maskell scales on pines) or for reaching scales on hard-to-spray specimen trees.  

Buprofezin, fenoxycarb, and pyriproxifen are insect growth regulator insecticides, with varying impact on the predators and parasitoid natural enemies of scales.  Buprofezin is reported to have minimal impact on ladybeetles and parasitoids, while pyriproxifen has successfully been used in combination with parasitoids for integrated scale management. 

Table 1.  Primary scale pests of ornamentals in Connecticut and their hosts (Adapted from K. Welch and T. Abbey, Pesticide Guide Toward Integrated Pest Management for Connecticut Nurseries 2006)
Soft scales
Common name	Scientific name	Hosts
azalea bark scale	Eriococcus azaleae	Pieris japonica, Populus, Rhododendron, Salix
beech scale	Cryptococcus fagisuga	Fagus
calico scale	Eulecanium cerasorum.	Pyracantha
cottony camellia (taxus) scale	Pulvinaria floccifera	Acer, Cornus, Euonymus alatus, Ilex verticellata, Prunus spp., Rhododendron,  Taxus,
cottony maple scale	Pulvinaria innumerabilis	Acer, Celtis occidentalis Cornus, Crataegus, Euonymus, Fagus, Gleditsia tricanthus, Morus, Platanus occidentales, Populus, Rosa, Salix, Spiraea, Prunas persica, Pyris comunis, Quercus, Syringa, Tilia, Ulmus
cottony maple leaf scale	Pulvinaria acericola	Acer, Cornus, Lonicera, Nyssa sylvatica, Pieris japonica
European fruit lecanium	Parthenolecanium corni	Acer, Cercis Canadensis, Populus, Quercus, Ulmus
Fletcher scale	Parthenolecanium fletcheri	Taxus, Thuja
Greenhouse orthezia	Orthezia insignis (an ensign scale)	polyphagous
large hickory lecanium	Eulecanium caryae	Betula, Carya, Celtis occidentalis, Fagus, Gleditsia tricanthus, Juglans, Malus, Morus, Platanus occidentalis, Prunus persica, Quercus, Salix
magnolia scale	Neolecanium cornuparvum	Magnolia, Wisteria
pine tortoise scale	Toumeyella parvicornis	Pinus
spruce bud scale	Physokermes piceae	Picea
terrapin scale	Mesolecanium nigrofasciatum	Betula, Cercis canadensis, Crataegus,Morus, Platanus occidentalis, Populus, Prunus amygdalus, Prunus, Tilia
tuliptree scale	Toumeyella liriodendri	Hypericula cistifolium, Magnolia, Tilia
Armored scales
circular hemlock scale	Nuculaspis tsugae	Tsuga
elongate hemlock	Fiorinia externa	Abies, Picea, Tsuga
euonymus scale	Unaspis euonymi	Daphne, Euonymus, Ligustrum, Lonicera, Syringa
fern scale	Pinnaspis aspidistrae.	Filices
juniper scale	Carulaspis juniperi	Calocedrus, Chamaecyparis, Juniperus, Thuja
oleander scale	Aspidiotus nerii	Many hosts, including Buddleia, Cercis canadensis, Daphne, Elaegnus, Hypericum calycinum, Ligustrum, Nerium oleander, Taxus
oystershell scale	Lepidosaphes ulmi	Acer, Amelanchier, Calluna, Cotoneaster, Erica, Fraxinus, Hydrangea, Ilex, Malus, Populus, Spirea, Syringa, Viburnum
pine needle scale	Chionaspis pinifoliae	Picea, Pinus,
Putnam scale	Diaspidiotus ancylus.	Vaccinium
San Jose scale	Quadraspidiotus perniciosus	Many hosts, including Buxus, Cornus, Cotinus, Cotoneater, Crataegus, Jugalns, Ligustrum, Morus, Populus, Pyracantha, Rosa, Sorbus, Tilia, Viburnum lentago
scurfy scale	Chionaspis furfura	Ribes
walnut scale	Quadraspidiotus juglansregiae	Acer, Betula, Celtis occidentalis, Cornus, Fraxinus, Gleditsia tricanthus, Gymnocladius, Hamamelis, Ilex, Juglans, Ligustrum, Liquidambar, Populus, Sorbus, Tilia, Ulmus
white prunicola scale	Pseudaulacaspis prunicola	Koelreuteria paniculata, Prunus amygdalus, Prunus
Mealybugs
apple mealybug	Phenacoccus aceris	Acer, Castanea, Cinnamon, Cornus, Cotoneaster, Corylus, Crataegus, Diospyros, Kalmia, Lonicera, Magnolia, Malus, Morus, Myrica, Prunus, P. persica, P. serotina, Quercus, Tilia, Vaccinium
Comstock mealybug	Pseudococcus comstocki	Acer, Elaeagnus, Euonymus alatus, Ilex, Malus, Pinus, Populus, Ulmus, Viburnum, Weigelia, Wisteria
grape mealybug	Pseudococcus maritimus	Gingko biloba, Gleditsia tricanthus, Pyrus communis
ground mealybug	Rhizoecus falcifer	roots of anemone, chrysanthemum, gladiolus, iris, other flowers, shrubs, and ornamental grasses
Mexican mealybug	Phenacoccus gossypii	Geranium
obscure mealybug	Pseudococcus viburni	Broad host range; woody plants and vines including Malus, Pyris, Vitis, Rhododendron
taxus mealybug	Dysmicoccus wistariae	Taxus
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Table 2.  Insecticides for management of scales and mealybugs in woody ornamentals in Connecticut, 2009. (Adapted from K. Welch and T. Abbey, Pesticide Guide Toward Integrated Pest Management for Connecticut Nurseries 2006)  N = Nursery, L = Landscape, R = Restricted Use Pesticide
Insecticide	Trade name (examples)	Comments
acephate	Acephate Pro 75 (N, L), Orthene T, T and O (N, L)	not compatible with biocontrol
acetamiprid	TriStar 70 WSP (N, L)
azadirachtin	Azatrol (N, L), Ornazin 3 EC (N)
Beauveria bassiana	Botanigard ES (N, L), Botanigard WP (N, L)	mealybugs only
bifenthrin	Talstar Nursery Granular (N), Talstar Lawn and Tree Flowable (L)	mealybugs, San Jose scale crawlers
buprofezin	Talus (N, L)
carbaryl	Carbaryl 4 L (N, L), Carbaryl 50 WP (N, L),  Sevin SL (N, L)	not compatible with biocontrol
chlorpyrifos	Chlorpyrifos Pro 2 (see label for sites) R, Chlorpyrifos Pro 4(see label for sites) R, Dursban 50W (N) R	not compatible with biocontrol
clothianidin	Celero 16 WSG (N, L)	mealybugs only
cyfluthrin + imidacloprid	Discus (N)
cyfluthrin	Decathlon 20 WP (N), Tempo (L)
dimethoate	Cygon 2E (N), Dimethoate 267 (N), Dimethoate 400 (N)	not compatible with biocontrol
dinotefuran	Safari 20 SG (N, L)
fenpropathrin	Tame 2.4 EC (N)	mealybugs only
horticultural oil	Damoil (N, L), Sunspray UltraFine Spray Oil (N, L), Synergy Superfine Spray Oil (N, L)
imidacloprid	Marathon 1G (N), Marathon 60 WP (N), Marathon II (N)
insecticidal soap	Insecticidal Soap 49.52 CF, M-Pede (N, L)
malathion	Check labels for specific scales.	not compatible with biocontrol
methidathion	Supracide 2E (N) R	Scale crawlers
permethrin	Permethrin 3.2 AG (N, L) R, Permethrin 3.2 EC(N, L) R	mealybugs only, not compatible with biocontrol
phosmet	Imidan 70 W (N, L)	mealybugs only, not compatible with biocontrol
pyriproxifen	Distance IGR (N, L)
thiamethoxam	Flagship 25 WG (N)	Soft scales and mealybugs only
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Additional Resources 
Antonelli, A. L.  2003.  Scale Insects, Washington State University Cooperative Extension. http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls63scaleinsects.pdf 

Buss, E. A, and J. C. Turner.  2006. Scale Insects and Mealybugs on Ornamental Plants, Institute of Food and Agricultural Sciences, University of Florida, Gainesville.  http://edis.ifas.ufl.edu/document_mg005

Gilrein, D. Tipping the Scales.  http://www.groundsmag.com/mag/grounds_maintenance_tipping_scales/

Hodges, G.  Scale Insects.  Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville, Fl. http://www.ent.uga.edu/peach/peachhbk/insects/scaleinsects.pdf

Johnson, W. T. and H. H. Lyon.  1994.  Insects that Feed on Trees and Shrubs.  Cornell University Press, Ithaca, New York.

Muegge, M. A. and M. Merchant.  Scale Insects on Ornamental Plants.  Texas Agricultural Extension Service.  Texas A&M University. http://theurbanrancher.tamu.edu/retiredsite/bugs/b6097.pdf  

Please consult the Plant Pest Handbook and other fact sheets available on the Connecticut Agricultural Experiment Station website, www.ct.gov/caes for additional information on crop health and Connecticut agriculture.

Mention of a chemical or product is for informational purposes only and does not constitute an endorsement by The Connecticut Agricultural Experiment Station 

This fact sheet is not a substitute for the pesticide label. The applicator assumes all responsibility for the proper use of any pesticide and must always thoroughly read, understand, and follow all label directions.
 

fact sheet posted July 2009