heavy infestation of Japanese maple scale

Infestation on flowering dogwood bark
Photo: Brian Kunkel, University of Delaware, Bugwood.org

 

Updated: August 16, 2022

Key points

  • Japanese maple scale (Lopholeucaspis japonica) is a non-native type of armored scale insect that can be difficult to manage. Their waxy body covering shields them from predators and certain pesticides. Learn more about scale insect groups and biology in Introduction to Scale Insects.
  • This is a pest of a very broad range of trees and shrubs and can cause plant decline, dieback, or death when populations are high.
  • Target monitoring and control efforts to the vulnerable crawler stage. Learn more about what to look for in Monitoring for Scale.

Appearance

  • Mature female covers are oystershell-shaped, dark brown with a thin white coating, and less than ⅛” (3 mm) in length.
  • Male covers are similar and smaller.
  • Crawlers are purplish.
    magnified image of Japanese maple scale
    Magnification helps to detect scale that are wedged into bark cracks
    Photo: John .A. Davidson, Univ. Md, College Pk, Bugwood.org

Common host plants

Dozens of species in over 27 plant families are used by this species. This is not an exhaustive list.

  • larger-statured trees, including maple (Acer), elm (Ulmus), zelkova (Zelkova), birch (Betula), honeylocust (Gleditsia),beech (Fagus), chestnut (Castanea), sweetgum (Liquidambar), tulip poplar (Liriodendron), magnolia (Magnolia), willow (Salix), and linden (Tilia)
  • smaller-statured trees, including serviceberry (Amelanchier), redbud (Cercis), crabapple (Malus), hornbeam (Carpinus), dogwood (Cornus), hawthorn (Crataegus), silverbell (Halesia), snowbell (Styrax), stewartia (Stewartia)
  • broadleaf evergreens, including holly (Ilex), boxwood (Buxus), privet (Ligustrum; invasive), Japanese euonymus (Euonymus japonicus), firethorn (Pyracantha), and camellia (Camellia)
  • deciduous shrubs and vines, including chokeberry (Aronia), cotoneaster (Cotoneaster), lilac (Syringa), flowering quince (Chaenomeles), panicle Hydrangea (Hydrangea paniculata), Smokebush (Cotinus coggygria), and Wisteria (Wisteria)
  • fruit trees and shrubs, including apple (Malus), Pear (Pyrus), Persimmon (Diospyros), Jujube (Ziziphus), Quince (Cydonia and Pseudocydonia), and Fig (Ficus)

Where to look

  • Mature females and immature males will be found on the bark of branches of all sizes.
  • Light infestations often start in the bark cracks and rough areas of the trunk and branches. 
  • Japanese maple scale near wound callus tissue

    Look near wound callus tissue for new scale populations

    Photo: David L. Clement, University of Maryland, Bugwood.org

    Click on image to enlarge.

  • Well-camouflaged Japanese maple scale on an elm tree

    Scale can begin accumulating in bark fissures and will be very well-camouflaged. This is an elm.

    Photo: Joe Boggs, OSU Extension

    Click on image to enlarge.

  • large population of Japanese maple scale on elm twig

    Even large scale populations can blend in with the bark

     For host trees with smoother young bark (such as maples), look for a texture difference and rough areas when monitoring for scale outbreaks.
    Photo: Joe Boggs, OSU Extension

    Click on image to enlarge.

Plant damage

  • Moderate infestations may result in leaf yellowing and loss, stagnated growth, or stunting.
  • Heavy infestations can result in the death of branches or entire plants.

Life cycle

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

Management

Refer to our general scale management recommendations (link below) for both chemical-based and pesticide-free options. When pesticides are warranted, a combination of dormant oil applications and the use of systemic or growth-regulating insecticides is the most effective approach. For large populations, scale suppression may require more than one year of intervention, and professional pesticide applicators will be needed to apply certain treatments. Mature trees should be evaluated by a certified arborist.

The long egg-laying and crawler emergence period for this species means that monitoring and treatment will need to occur several times a year to be effective. If you do not wish to use pesticides and are not obtaining good control from manual removal efforts alone, remove and replace the infested plants.

When not too weakened, several of the deciduous and evergreen shrubs listed as hosts will regenerate well from harsh pruning. Cut back heavily-infested plants almost to the ground so regrowth will be easier to monitor; this also greatly reduces pesticide use since there will be fewer plant surfaces to spray.

Pesticide sprays should be avoided when red-spotted black lady beetles are present, as they are a scale predator. Similarly, at least four species of parasitoids are known to attack this scale in the mid-Atlantic area. Look for holes in scale covers as an indicator natural enemies are present.

Introduction to Scale Insects
Timing details for monitoring and pesticide use

Just before the expected emergence period for each generation, 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. Here are refined estimates of egg hatch and the beginning of crawler emergence:

  • First generation – 815 to 829 degree days
    • During the peak flowering of Smokebush (Cotinus coggygria) and Chinese Lilac (Syringa chinensis)
  • white smokebush blooms

    Smokebush bloom

    Photo: Miri Talabac

  • lilac shrub flower

    Lilac bloom

    Photo: Miri Talabac

  • Second generation – 2220 to 2508 degree days
    • Before the flowering of Devil’s Walkingstick (Aralia spinosa)
    • Before the peak flowering of Natchez Crapemyrtle (Lagerstroemia ‘Natchez’)
    • After the first flowering of Hollow Joe-Pye Weed (Eutrochium fistulosum)
  • Devil's walking stick in bloom

    Devil’s Walkingstick colony in bloom

    Photo: Miri Talabac

  • Crapemyrtle 'Natchez' with white flowers

    Crapemyrtle bloom

  • blooming joe pye weed

    Joe-Pye weed bloom

    Photo: Miri Talabac

References:
Adapted from, Managing Insects and Mites on Woody Plants, authors: Ph.D. John A. Davidson, Ph.D.and Michael J. Raupp, Ph.D. The Pest Predictive Calendar, and Scale Crawler Emergence Period chart compiled by Stanton Gill, Suzanne Klick, and Sarah Kenney.

Author: Miri Talabac, Horticulturist & Coordinator, HGIC 2022