Gloomy Scale
The
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. 
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.
Heavily infested maples are unthrifty. The bark becomes dark with molds
and grainy 
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.
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.
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.
Web page last reviewed January, 2011 by the webperson.