Gloomy Scale on Maples

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Q: My maple trees with dark bumps on the bark. What is going on?

 A:      Maples are a popular tree in the landscape and why wouldn’t they be. Maples provide plenty of shade in the summer and have wonderful fall color. Unfortunately there is pest that commonly occurs on maples along with other trees called gloomy scale.

Gloomy scale is an insect that protects its self with a small covering. Gloomy scale occurs on the soft maples like silver and red maple. Although less commonly seen, gloomy scale can also infect grapes, native hollies, sweetgum, and mulberry.

Gloomy scale attaches to the bark of the tree’s trunk and branches. It will as appear as dark, almost black, bumps on the bark. When a heavy infestation occurs, the bark will become covered with those dark bumps giving the appearance of a mold occurring on the bark. Infestations can be so bad that the trunk and branches can be completely covered sometimes two or three layers deep. Often when the bark is heavily covered with gloomy scale, people mistake it for a mold instead of an insect. With a heavily infestation, branch dieback will occur. Gloomy scale does overwinter and will continue to increase in number through the spring.

Since gloomy scale has a covering for protection, control can be difficult because you have to reach the insect for an insecticide to work. Spraying a horticulture or dormant oil on an infested tree now during the dormant season will probably be the most effective chemical treatment. Be sure to not spray dormant oil during the growing season, because the oil can damage growing buds and leaves on the tree. There are horticulture oils that can be sprayed in the summer, so be sure to read the label to see when the product you are considering should be sprayed. For large trees, spraying may not be worth while because it will be more difficult to get the thorough coverage that is needed for control.

Improving growing conditions for infested trees will also help control gloomy scale. Stressed trees are going to be more prone to being infected by insect and diseases. If you have not before, submit a soil sample to check that the soil pH and nutrients are in balance. Proper amount of fertilizer according to your soil test results will encourage good tree growth. Do not just assume that applying some 8-8-8 or 10-10-10 every year works. Call the Wayne County Extension office for more information on how to submit a soil sample. During times of prolonged drought, trees should be watered regularly. Instead of having grass growing under the infested tree, have a layer of mulch so that the grass isn’t taking up the water and nutrients before it can get to the tree roots.

Gloomy scale can be a troublesome pest often on silver and red maples, but with proper tree care and catching the scale when it first starts can prevent gloomy scale from turning into a larger, more difficult problem later on.

Recommendations for the use of agricultural chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this article does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.

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Jessica Strickland is an Agriculture Extension Agent, specializing in horticulture for North Carolina Cooperative Extension in Wayne County. Horticulture program information can be found at // Forward any questions you would like answered from this week’s column to

Written By

Jessica Strickland, N.C. Cooperative ExtensionJessica StricklandInterim County Extension Director & Extension Agent, Agriculture - Horticulture Call Jessica Email Jessica N.C. Cooperative Extension, Wayne County Center
Updated on Oct 9, 2020
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