Close-up of mature European fruit lecanium scale on a young twig
Photo: D.K.B Cheung
Updated: August 16, 2022
Key points
European fruit lecanium scale (Parthenolecanium corni), despite the name, 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 maple and fruit trees and an array of other trees and shrubs. The pest can cause stunting and dieback 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 or variable in shape (may be two-humped), assorted hues of brown (sometimes with black markings), and up to ¼” (6 mm) in diameter.
Male covers are elongated, ridged and somewhat transparent, and smaller in size.
Crawlers are white, turning yellow.
Crawlers settling along sugar maple leaf veins
Photo: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Bugwood.org
Mature scale on an oak twig
Photo: Joe Boggs, OSU Extension
Common host plants
Fifty plant families are utilized as hosts by this species, including many popular flowering shrubs, fruiting shrubs and trees, and shade trees.
Maples (Acer) and ornamental fruit trees (Prunus, Malus) are preferred.
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.
Well-camouflaged female scale between dormant buds
Photo: D.K.B Cheung
Trees under stress. Paved surfaces reflect heat and limit soil moisture, and trees exposed to this stress are more prone to damaging infestations of lecanium scale.
Use of pyrethroid-type insecticides, such as in aerial mosquito treatments, has been associated with outbreaks of lecanium scale due to its broad-spectrum harm to natural enemies.
Plant Damage
Moderate to heavy infestations will produce honeydew, which can attract other insects (mainly flies, wasps, and ants) and support the growth of sooty mold. This tends to be most prominent beginning in May.
Heavy or prolonged infestations can cause leaf drop, stunted growth, and twig dieback, especially following maturation of the females in mid-spring into early summer.
The crawler emergence period depends on temperature and can vary slightly from year to year. The approximate time to monitor for them is mid-May through mid-September.
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 lecanium 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.
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:
904 degree days
After the peak flowering of Smokebush (Cotinus coggygria)
During the start of the flowering of Japanese Stewartia (Stewartia pseudocamellia)
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.
