Female calico scale infesting honeylocust
Photo: Joe Boggs, OSU Extension
Updated: August 16, 2022
Key points
Calico scale (Eulecanium cerasorum) is a native type of soft scale insect and can be difficult to manage. Their waxy body covering shields them from predators and certain pesticides. Learn more about scale insect groups and biology on Introduction to Scale Insects.
This is a common pest of flowering, shade, and stone fruit trees, and can cause stunting and premature leaf drop when populations are high.
Target monitoring and control efforts to the vulnerable crawler stage. Learn more about what to look for on Monitoring for Scale.
Appearance
Mature female covers are hemispherical, black with white spots (turning brown in death), and up to ¼” (6 mm) in diameter.
There are no males.
Crawlers are white, turning yellow.
Juvenile and adult calico scale
Illustration: J.A. Davidson
Click image to open
Close-up of calico scale crawlers amid dead females
Photo: Joe Boggs, OSU Extension
Juvenile calico scale on honeylocust stem
Photo: Joe Boggs, OSU Extension
Common host plants
Shade trees, including elm (Ulmus), zelkova (Zelkova), sweetgum (Liquidambar), maple (Acer), and honeylocust (Gleditsia).
Flowering trees, including dogwood (Cornus), star magnolia (Magnolia stellata), cherry (Prunus), and crabapple (Malus).
A few other woody plants, including firethorn (Pyracantha) and possibly wisteria (Wisteria) - note Japanese wisteria is an invasive vine.
Where to look
In winter, both living juveniles and larger, dead females from a prior generation will be found on twigs.
In summer, juveniles will feed on foliage alongside the veins.
Trees under stress. Paved surfaces reflect heat and limit soil moisture, and trees exposed to this stress are more prone to damaging infestations of calico scale.
Crawlers tend to blend-in well as they settle along leaf veins. These are honeylocust leaflets.
Photo: Joe Boggs, OSU Extension
Example of crawlers settling along veins on maple
Photo: Joe Boggs, OSU Extension
Plant damage
Crawler feeding on the foliage in summer usually causes no symptoms.
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 leaf yellowing, stunting, and premature shedding.
Sooty mold darkening the bark of an infested Honeylocust. The scale would be found on the leaves or branches above the mold.
Photo: Joe Boggs, OSU Extension
Honeydew droplets being secreted by mature calico scale
Photo: Joe Boggs, OSU Extension
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 mid-June through early October.
They overwinter on the bark as juveniles.
Management
Refer to our general scale management recommendations 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.
While calico scale crawlers can be treated with foliar-absorbed pesticides at any point during summer, these options are not as low-impact on other insects, nor are they practical for mature trees.
Naturally-occurring beneficials usually suppress calico scale. Look for lady beetles and other natural enemies before deciding to use pesticides.
Natural enemy (twice-stabbed lady beetle) consuming scale
Photo: Joe Boggs, OSU Extension
Timing details for monitoring and pesticide use
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. Here is a refined estimate of egg hatch and the beginning of crawler emergence:
765 degree days
After the peak flowering of Virginia spiderwort (Tradescantia virginiana)
Before the peak flowering of smokebush (Cotinus coggygria)
Calico Scale | Ohio State University’s newsletter Buckeye Yard and Garden on Line
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.
