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Gloomy Scale

James R. Baker and S. B. Bambara, Extension Entomologists

CAUTION: This information was developed for North Carolina and may not apply to other areas.

GLOOMY SCALE, *Melanaspis tenebricosa (Comstock),Diaspididae, HOMOPTERA

General Information

female scale exposed under coverThe armor of female gloomy scales is up to 1/16 inch wide with a central pale ring that may weather away. The armor is convex and is usually the same color as the bark. Females are yellowish or pink to purple, legless and wingless, but they have long, piercing-sucking mouthparts. Males are tiny (up to 1/32 inch long) gnat-like insects. The crawlers are microscopic (1/64 inch long) and flattened. They are cream colored and have brown eyes. Each crawler has six legs and two antennae. The armor of very young scales is circular with a pale edge. armor flipped over

Female nymphs resemble the adult except for smaller size. The armor is also smaller. Male nymphs are elongate and their armor is oblong with the pale ring toward one end.

Biology

Gloomy scales are found from Texas to Florida and north to Michigan and Pennsylvania on maples, especially the soft maples (boxelder, red maple and silver maple). Grape, soapberry, native hollies, mulberry, sweetgum, and buckthorn are also infested.

Heavily infested maples are unthrifty. The bark becomes dark with molds and grainy rough, black scale group from the armor of the scales. Significant twig dieback occurs. The scales probably cause dieback by injecting saliva into the trees as they feed.

Gloomy scales overwinter as mated females. Development resumes in April and the first crawlers are produced in May. Crawlers are produced until the middle of August at which time practically every stage of development can be found. Males emerge in August and September and mate with new females. There is one generation per year.

Soon after oviposition (23 to 48 hours), crawlers emerge from under the mother to search for a suitable feeding site. On sparsely populated stems, crawlers usually settle near twig crotches and buds. The whole surface of stems may be completely covered by scales, sometimes two or three layers deep. After inserting the mouthparts, crawlers tuck in their legs and antennae and begin secreting the armor. After molting, female scales do not have legs or antennae. Male crawlers also molt into legless scales, but in July and August males molt into 'prepupae' and 'pupae', stages in which the legs and wings once again develop. In August, the winged males emerge and crawl or fly to female scales and mate. Apparently, female scales molt one more time in the fall after mating.

Control

A horticultural oil as a dormant application is probably the most effective chemical treatment for gloomy scale control. However, sometimes trees are so large that thorough coverage is difficult. In such cases, it would probably be better to try to treat for the scales by improving the growing conditions of the trees. First, submit a soil sample from under the infested tree to the NCDA&CS Soils Lab. If the pH or nutrients are unbalanced, the soil should be amended. During periods of prolonged drought, the trees should be irrigated. Grass under infested trees could be killed and the soil mulched to conserve soil moisture and keep the roots cool. Anything within reason should be done to enhance the vitality of the trees without stimulating excessive growth (that is, fertilize the amount indicated on the NCDA&CS analysis sheet, don't just apply a bunch of 8-8-8 or 10-10-10). It is known that trees under stress have more simple sugars (rather than starches) and more free amino acids (rather than more complex proteins) in the sap. Thus stressed trees may be more nutritious to the scales than healthy trees. The bark of unsprayed trees is often like a microscopic zoo with all sorts of predaceous mites, predaceous insects, parasitic insects, parasitic fungi and other organisms in addition to the scales.

By getting the tree into top growing condition, it should be less susceptible to the scales and the scales will not reproduce as prolifically. As a consequence, the parasites and predators may control the scales almost completely.

In case the tree is small enough to spray, there are many brands of horticultural oils on the market with various rates of application. When treating for gloomy scales during the dormant season, use the highest rate on the label. The best time to treat for gloomy scale is in early spring as the buds are beginning to swell and gloomy scale development is resuming. But once the buds break in early spring, it is too late to apply horticultural oil at the high rate without the risk of significant damage to the tree. Use the summer rate on plants with mature foliage. Dinotefuran (Safari) is a systemic applied as soil drench or bark spray, that may be helpful in the long term, if applied early in the season so that it has time for uptake.  Acephate (Orthene, Orthenex) may be used during the growing season, however, it has the disadvantage of killing beneficial insects also. When using any pesticide, be sure to read the label for the proper concentration and directions for safe use. If the tree is small enough, there may some advantage to pressure washing scale encrusted bark with water, but be careful not to use too much pressure that can damage the bark itself!

There is additional information on horticultural oils in Ornamentals and Turf Insect Information Note 45.


Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

© 2001 NC Cooperative Extension Service
Prepared by: James R. Baker & S. B. Bambara, Extension Entomologists
ENT/ort-60

Web page last reviewed January, 2011 by the webperson.