closeup of European Fruit Lecanium Scale on twig

Cluster of mature European fruit lecanium scale on a young twig
Photo: D.K.B Cheung

Updated: August 16, 2022

Key points

  • Learn more about scale insect groups, biology, and management on Introduction to Scale Insects.
  • Inspect ailing plants and learn how to find scale insects using the information on Monitoring for Scale.
  • Numerous scale species can occur in home gardens, though they may not be noticed unless plants show signs of damage. Signs of soft scale infestation include honeydew and sooty mold. Symptoms of plant damage include leaf yellowing, stunting of growth, and branch dieback.
  • Small populations of scale are rarely a concern, and landscapes that support natural enemies benefit from a lower likelihood of outbreaks. Gardens incorporating a diverse range of plant species attract and retain populations of natural enemies.

Common soft scale species in Maryland gardens

  • white sacs created by cottony camellia scale on a leaf

    Cottony Camellia Scale

    Photo: Brian Kunkel, University of Delaware, Bugwood.org

  • A single indian wax scale on a twig

    Indian Wax Scale

    Photo: Matt Bertone, NC State University

  • Adult Tuliptree scale cluster with alive dead adults

    Tuliptree Scale

    Photo: Joe Boggs, OSU Extension

  • calico scale closeup on twig

    Calico Scale

    Photo: Joe Boggs, OSU Extension

  • closeup of European Fruit Lecanium Scale on twig

    European Fruit Lecanium Scale

    Photo: D.K.B Cheung

  • closeup of oak lecanium scale on twit

    Oak Lecanium Scale

    Photo: Joe Boggs, OSU Extension

  • a branch covered in crapemyrtle bark scale

    Crapemyrtle Bark Scale

    Photo: Jim Robbins, Univ. of Ark. CES, Bugwood.org

Occasional soft scale species in Maryland gardens

Magnolia scale (Neolecanium cornuparvum)

This is a native scale species.

Appearance

 

closeup of magnolia scale
While older growth can harbor the scale, young twigs are where infestations typically begin
Photo: Brian Kunkel, University of Delaware
  • Mature female covers are oval to hemispherical or irregularly shaped, white to yellowish to purplish-brown, and up to ½” (12.5mm) in diameter.
  • Male covers are oval, white, and much smaller.
  • Crawlers are black. 
magnolia scale crawlers on branch tended by ants
Crawlers on a branch wound callus, tended by ants
Photo: Sarah Vanek, Bugwood.org

Common Host Plants

  • Magnolias, especially star magnolia (Magnolia stellata), cucumber tree (Magnolia acuminata), lily magnolia (Magnolia liliiflora), and saucer magnolia (Magnolia x soulangiana)

Where to Look

  • All life stages will be found on the bark, especially on one- to two-year-old twigs.
  • Ants often protect colonies of this scale in order to feed on the honeydew. Examine busy ant trails on young host plants to see if they are tending a population of scale in the canopy.

 

ants tending scale on a magnolia
Mature magnolia scale tended by ants
Photo: Sarah Vanek, Bugwood.org

Plant Damage

  • Moderate to heavy infestations will produce large quantities of honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
  • Heavy or prolonged infestations can cause premature leaf shedding, reduced foliage production, reduced blooming, and potentially branch dieback.

Life Cycle

  • There is 1 generation per year in Maryland.
  • The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is September.
  • They overwinter on the bark as juveniles.
  • Juveniles can be so numerous that they appear to be normal features of the bark. They appear as numerous small, dark ovals on bark.

Timing Details for Monitoring and Treatment

No local Growing Degree Days and Plant Phenological Indicator data have been compiled for this species.

Azalea bark scale (Eriococcus azaleae)

This is a non-native scale species.

Appearance

closeup of azalea bark scale
Adult Azalea Bark Scale, with and without “felt.”
Photo: United States National Collection of Scale Insects Photographs, USDA Agricultural Research Service, Bugwood.org
  • Mature female covers are oval, dark reddish-purple covered in white felt, and up to ⅛” (3mm) long.
  • Male covers are oval, white, and smaller.
  • Crawlers are reddish.

Common Host Plants

  • Prefers azaleas and rhododendrons (both are members of genus Rhododendron) and relative Andromeda/Pieris (Pieris)
  • Several other species of flowering shrubs, trees, and evergreens, including ornamental cherry (Prunus), hawthorn (Crataegus), willow (Salix), poplar (Populus), maple (Acer), hackberry (Celtis), and arborvitae (Thuja)

Where to Look

azalea bark scale near forks in a twig

Look near twig forks for outbreaks.
Photo: Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org
  • All life stages will be found on the bark, especially in twig forks when populations are low.

Plant Damage

  • Light populations usually cause no plant symptoms but do produce honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
  • High populations can cause leaf yellowing and twig dieback. Prolonged infestations can kill plants after a few years.

Life Cycle

  • There are 2 generations per year in Maryland.
  • The crawler emergence periods depend on temperature and can vary slightly from year to year. The approximate times to monitor for them are:
    • First generation – late May to mid-June
    • Second generation – late June to mid-July
  • They overwinter on the bark as juveniles.

Timing Details for Monitoring and Treatment

 

European Elm Scale (Gossyparia spuria)

This is a non-native species.

Appearance

european elm scale on branch

Males and adult females on the underside of a branch.
Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
  • Mature female covers are oval, dark reddish-brown with a white margin, and up to ⅛” (3mm) long.
  • Male covers are elongated, white, and smaller.
  • Crawlers are yellow.

Common Host Plants

  • Prefers elm (Ulmus) and may occur more rarely on its relative zelkova (Zelkova); also redbud (Cercis)

Where to Look

  • In winter, juveniles and adult females will be found on twigs, especially in branch forks (adults) and in bark cracks (juveniles).
  • In summer, juveniles will feed on foliage alongside the veins.
european elm scale crawlers along leaf veins
Juveniles (crawlers) along leaf veins
Photo: Whitney Cranshaw, Colorado State University, Bugwood.org
  • Trees under stress. Recent transplants or young trees growing in challenging conditions are more prone to damaging infestations of this scale.

Plant Damage

  • Moderate to heavy infestations will produce large quantities of honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
  • Heavy or prolonged infestations can cause premature leaf shedding, stunted growth, and dieback.

Life Cycle

  • There is 1 generation per year in Maryland.
  • The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is early May through mid-October.
  • They overwinter on the bark as juveniles.

Timing Details for Monitoring and Treatment

Just before the expected emergence period, start monitoring for crawlers. Since weather trends can shift date ranges, a more reliable prediction of timing can be made using Growing Degree Days and Plant Phenological Indicators. A refined estimate of egg hatch and the beginning of crawler emergence is:

831 degree days

After the peak flowering of Virginia spiderwort (Tradescantia virginiana)

purple spiderwort
Spiderwort flower
Photo: Miri Talabac

Before the peak flowering of smokebush (Cotinus coggygria)

smokebush in bloom
Smokebush bloom
Photo: Miri Talabac

Natural enemies usually provide adequate control without the need for pesticides.

Cottony maple scale (Neopulvinaria innumerabilis)

This is a native species.

Appearance

closeup of adult scale with ovisac
Mature female producing an ovisac.
Photo: D.K.B Cheung
  • Mature female covers are oval, black, and up to 3/16” (4.75mm) long. The cottony white ovisac (egg case) they produce behind their covers are about ¼” (6 mm) in length.
  • Crawlers are tan.

Common host plants

Twenty-nine plant families are used by this species.

 

  • Preferences among flowering and shade trees include maple (Acer), elm (Ulmus), hawthorn (Crataegus), dogwood (Cornus), sycamore (Platanus occidentalis), poplar (Populus), and linden (Tilia)
  • Preferred vines include grape (Vitis) and its relatives (Parthenocissus)

Where to look

  • In winter, juveniles and adult females will be found on bark.
  • In summer, juveniles will feed on foliage alongside the veins.
closeup of cottony maple scale nymphs on a twig

Nymphs on a Hawthorn twig.
Photo: Raymond Gill, California Department of Food and Agriculture, Bugwood.org

Plant damage

  • Light to moderate populations usually cause no plant symptoms but do produce honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
  • Heavy or prolonged infestations can cause premature leaf yellowing, stunted growth, and dieback.
     

Life cycle

  • There is 1 generation per year in Maryland.
  • The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is June.
  • They overwinter on the bark as juveniles.
    brown cottony maple scale adult
    Cottony maple scale mature female.
    Photo: D.K.B Cheung

Timing details for monitoring and treatment

Just before the expected emergence period, start monitoring for crawlers. Since weather trends can shift date ranges, a more reliable prediction of timing can be made using Growing Degree Days and Plant Phenological Indicators. A refined estimate of egg hatch and the beginning of crawler emergence is:

872 degree days

  • After the peak flowering of Smokebush (Cotinus coggygria)
  • Before the first flowering of Japanese Stewartia (Stewartia pseudocamellia)
smokebush in bloom
Smokebush bloom
Photo: Miri Talabac
white bloom of Japanese stewartia tree
Japanese Stewartia bloom
Photo: Miri Talabac

Fletcher Scale (Parthenolecanium fletcheri)

 This is a native species.

Fletcher scale (Parthenolecanium fletcheri)

This is a native species.

 

Appearance

fletcher scale adult closeup
Fletcher scale adult.
Photo: D.K.B Cheung
  • Mature female covers are hemispherical, yellow-brown, and up to 3/16” (4.75mm) in diameter.
  • Crawlers are amber to pinkish-orange. 

Common Host Plants

  • Yew (Taxus), arborvitae (Thuja), juniper (Juniperus), cypress (Cupressus), and hemlock (Tsuga)

Where to Look

fletcher scale on baldcypress tree new growth
Fletcher scale on baldcypress
Photo: Joe Boggs, OSU Extension

 

  • All life stages can be found on twig tips.
  • From summer through winter, juveniles can also be found on foliage.

Plant Damage

baldcypress with brown needles caused by fletcher scale
Adult Fletcher scale nestled among juniper needles (leaves)
Photo: Bruce Watt, University of Maine, Bugwood.org
  • Light to moderate populations usually cause no plant symptoms but do produce honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
  • Heavy or prolonged infestations can cause premature needle yellowing and shedding; small shrubs may die.

Life Cycle

  • There is 1 generation per year in Maryland.
  • The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is June.
  • They overwinter on twigs and needles as juveniles.

Timing Details for Monitoring and Treatment

Just before the expected emergence period, start monitoring for crawlers. Since weather trends can shift date ranges, a more reliable prediction of timing can be made using Growing Degree Days and Plant Phenological Indicators. A refined estimate of egg hatch and the beginning of crawler emergence is:

1105 degree days

After the peak flowering of Japanese stewartia (Stewartia pseudocamellia)

white bloom of Japanese stewartia tree
Japanese stewartia bloom
Photo: Miri Talabac

Before the first flowering of bottlebrush buckeye (Aesculus parviflora)

white bottlebrush buckeye blooms
Bottlebrush buckeye bloom
Photo: Miri Talabac

    Spruce bud scale (Physokermes piceae)

    This is a native species.

    Appearance

    closeup of spruce bud scale
    Aptly named, spruce bud scale looks much like spruce buds
    Photo: Steven Katovich, Bugwood.org
    • Mature female covers are globular, reddish-brown, and up to ⅛” (3mm) in diameter. They may be lightly dusted in wax, resembling the dried resin that coats spruce buds.
    • Male covers are oval, transparent to white, and smaller.
    • Crawlers are pinkish or yellow-orange.

    Common Host Plants

    • Prefers spruce, especially Norway spruce (Picea abies), black spruce (Picea mariana), red spruce (Picea rubens), and white spruce (Picea glauca, which includes the popular cultivar ‘Conica’, called dwarf Alberta spruce)
    • Some pines (Pinus)

    Where to Look

    A cluster of Spruce Bud Scale can look like buds
    A cluster of Spruce Bud Scale resembling buds at the base of young growth
    Photo: Edward H. Holsten, USDA Forest Service, Bugwood.org

     

    •  Near the tips of young growth, especially since mature females look very similar to spruce needle buds. Inspect bud scales (the protective coverings over developing or dormant buds) for scale nestled behind them as camouflage.
    • Lower branches are attacked more often than upper branches.

    Plant Damage

    • Light populations may not cause plant symptoms but do produce honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
    • High populations can weaken trees, reducing vigor, stunting growth, and making them more vulnerable to infection and winter burn.

    Life Cycle

    • There is 1 generation per year in Maryland.
    • The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is late June into July.
    • They overwinter at the base of foliage as juveniles.

    Timing Details for Monitoring and Treatment

    No local Growing Degree Days and Plant Phenological Indicator data have been compiled for this species.

    Pine tortoise scale (Toumeyella parvicornis)

    This is a native species.

    Appearance

    closeup of pine tortoise scale
    Mature female with small crawlers on top
    Photo: Jill O'Donnell, MSU Extension, Bugwood.org
    • Mature female covers are hemispherical, dark brown to black with mottling in tan or cream, and up to ¼” (6mm) in diameter.
    • Male covers are elongate, flat, translucent, and smaller.
    • Crawlers are reddish.

    Common Host Plants

    • Prefers pine, especially Scotch pine (Pinus sylvestris), Virginia pine (Pinus virginiana), and Jack pine (Pinus banksiana). Also utilizes Austrian pine (Pinus nigra), mountain pine (Pinus mugo), red pine (Pinus resinosa), eastern white pine (Pinus strobus), loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), and slash pine (Pinus elliottii)

    Where to Look

    pine tortoise scale at the base of the needles
    Mature females at the base of needles
    Photo: D.K.B Cheung
    • All life stages will be found on the twig tips. Look for adult females at the base of needles.
    • Abundant ants seeking honeydew are often associated with populations of this scale.

    Plant Damage

    • Light to moderate populations usually cause no plant symptoms but do produce honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold.
    • High populations can cause needle yellowing and branch dieback. Prolonged infestations can kill small plants, especially when combined with environmental stress (such as drought or wind desiccation).

    Life Cycle

    • There is 1 generation per year in Maryland.
    • The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is June through early July.
    • They overwinter on twigs as juveniles.

    Timing Details for Monitoring and Treatment

    No local Growing Degree Days and Plant Phenological Indicator data have been compiled for this species.

    References:
    Adapted from
    Managing Insects and Mites on Woody Plants: an IPM Approach by Dr. John A. Davidson and Dr. Michael J. Raupp

    The Pest Predictive Calendar
    - Scale Crawler Emergence Period chart compiled by Stanton Gill, Suzanne Klick, and Sarah Kenney.

    Compiled by Miri Talabac, Horticulturist Coordinator, HGIC 2022