Magnified view of a gloomy scale (Melanaspis tenebricosa) insect with its protective cover removed. The maple branch in the photo is almost completely covered with well-camouflaged scale covers.
Photo: Matt Bertone, NC State University
Updated: August 16, 2022
Key points
Gloomy scale (Melanaspis tenebricosa) is a native type of armored scale insect and can be difficult to manage as 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 common pest of maple and can cause a gradual plant decline and branch dieback as the scale population grows. Multiple other tree species as well as grape vines can also serve as host plants.
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 circular, gray with a black center, and up to ⅛” (3 mm) in diameter.
Male covers are oval, similar in color, and smaller.
Crawlers are orange.
Gloomy scale circular, bulls-eye like cover.
Illustration by J.A. Davidson
Branch encrusted with high numbers of gloomy scale.
Photo: Eric Honeycutt, Bartlett Tree Experts, Bugwood.org
Common host plants
most frequently red maple (Acer rubrum) and sugar maple (Acer saccharum)
a variety of large-statured trees, including catalpa (Catalpa), hackberry (Celtis), mulberry (Morus), sycamore and planetree (Platanus), elm (Ulmus), sweetgum (Liquidambar), tulip poplar (Liriodendron), black locust (Robinia), and willow (Salix)
grape vines (Vitis) and hollies (Ilex)
High population of Gloomy Scale on a Red Maple branch.
Photo: Adam Dale, North Carolina State University
Where to look
Gloomy scale will be found on the bark of the trunk and branches. Preferred sites are one- to four-year-old branches.
Trees under stress. Paved surfaces reflect heat and limit soil moisture, and trees exposed to this stress are more prone to damaging infestations of gloomy scale. Similarly, over-fertilization with nitrogen (like from excessive turf applications) also predisposes trees to high scale populations. Sites near dusty or unpaved roads additionally limit the ability of natural enemies to suppress scale populations.
High populations and successive generations can completely cover the bark, with individual scale covers overlapping each other. Infested bark will have a finely warty (seen up-close) or coarsely grainy (seen at a distance) texture, which is noticeably distinct from the smooth bark of certain host plants, notably young maples. Note that the covers of dead scale may remain attached for several years.
Plant damage
Moderate infestations may result in stagnated growth, stunting, or twig dieback.
Heavy or prolonged infestations can result in the death of branches and canopy thinning, or the death of entire plants.
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 between mid-July and late August.
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.
The single generation means that monitoring and treatment will need to occur in a relatively limited timeframe. 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.
Before deciding to use insecticides, look for parasitoid emergence holes in scale covers, as these indicate the level of control provided by natural enemies.
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.
