Pests and Diseases: Gloomy Scale


Gloomy Scale – it doesn’t have a particularly interesting name or conjure up images of anything too vile. I’d like to introduce to an insect that you’ve probably seen hundreds of times but not even realized it. Gloomy Scale’s latin name is Melanaspis tenebricosus and it is found all throughout the Mid-Atlantic region. Let’s look at the life cycle of Gloomy Scale before we discuss its control options because without understanding this, control is virtually impossible.

Scale in general can be broken down into two types: Armored scale and Soft scale. Soft scale can resemble little balls of cotton (Cottony cushion scale) or have similar fluffy-like appearances. Armored scale, such as Gloomy Scale, aren’t nearly as obvious and can go undetected for years and build to damaging populations. Gloomy scale resembles little flat gray colored discs that can be found on the trunks and stems of its victims. The discs that are visible are the outer covering that the adults produce to protect themselves. It is under this protective covering that all the dirty work is done. The adults lay their eggs here where they hatch into crawlers. These crawlers leave their parents and ensure that the infestation proceeds further on the plant. Once the babies have found an area that is suitable for them, they set up shop and begin producing their protective coating.

Scale feed by inserting their stylet (think of it as a straw) into the plant tissue and suck out its contents. As you can imagine, this isn’t good for the plant. Think of it like a tick on you, just sucking and sucking until it gets its fill. But with scale, it doesn’t really fill up per se…it just keeps producing babies that hang out to cause more misery. In cases of light infestations, the damage is usually minimal but remember, Gloomy Scale usually goes unnoticed and can build to heavier populations. It’s at these heavy populations that the damage becomes obvious but unfortunately, that’s when it’s harder to treat. Gloomy Scale is usually found on maples, particularly the red maple (Acer rubrum). Red maples will exhibit signs of decline such as dying branches, yellowing leaves and overall poor health. Of course, red maples can decline for many more reasons than just scale, but we’ll discuss that at another time.


Once you’ve determined that your maple is infected with these little monsters, you may have to wait to treat them. While that may sound counterintuitive, if we look back at the life cycle it will make perfect sense. If you are going to spray a contact insecticide, you have to spray when the crawlers are active, which is generally in May or June. If you spray a contact insecticide when the crawlers aren’t running around, all you’ve done is spray a toxic pesticide for no reason and wasted your money. Another more desirable option is to treat with a systemic insecticide. Systemic refers to the way that the chemical is delivered to the pest. In systemic pesticides, the chemical is taken up by the plant (usually through a root drench) and translocated throughout the vascular system to all areas of the plant. When an insect feeds on that plant, it receives a dose of the pesticide as well. There are lots of downsides to this method as well…look at my article on organic gardening vs. conventional gardening for more information.

The preferred method for treating scale is to apply a dormant horticultural oil during the winter months to smother and suffocate the overwintering scale. While it may not be a pleasant way to die for the scale, it certainly has the least amount of collateral damage to other insects, including beneficials. If you have a heavy infestation of gloomy scale on your maples, it may take several years to win the war against them, but to me, it is worth it to go slowly and avoid damaging the beneficial insects that visit the trees, including honeybees. The decision is ultimately yours and you have to remain diligent in scouting for Gloomy Scale either way.


My best advice is to try to replicate the natural environment that the plant is found in…in the case of Red Maple, that is a wet area. Red Maple is also known as Swamp Maple and its natural habitat is not in a parking lot island surrounded by 2 acres of asphalt. While the area doesn’t have to be a floodplain, red maple will do best in areas that are naturally more moist. Also try to help the trees out during very droughty times so that they aren’t more susceptible to pests in general, including Gloomy Scale. And lastly, reduce the amount of turf around the tree so that it has less competition with roots for water and nutrients. Just be sure that you go easy on the mulch…no mulch volcanoes please!

The next time you are out and about in your yard, take a glance at your maples and see if you are able to spot any grayish-black discs. If you do, invest in some dormant horticultural oil and smother these little beasts this winter. I’d love to hear your feedback after you’ve had some time to scout for them. Leave me a comment below or e-mail me at Happy scouting!


December 20, 2011Permalink 4 Comments

4 thoughts on “Pests and Diseases: Gloomy Scale

  1. Pingback: Pests and Diseases: Cottony Cushion Scale - Mid-Atlantic GardeningMid-Atlantic Gardening

  2. Pingback: Pests and Diseases: Glyphosate Damage to Trees | | Mid-Atlantic GardeningMid-Atlantic Gardening

  3. Here is Raleigh we often deal with trees that have gloomy scale. It is a major cause of dead and dying trees in our area and as such we get calls all the time from homeowners who need to have trees with gloomy scale removed. I am pleased to see an article discussing this important information for owners of maple trees with this problem.

  4. This article was very helpful to me- thank you. I have treated our tree for 2 years and the bark looks much healthier than the bark on trees nearby in our subdivision. It seems as if the leaves are fuller and last longer in the fall than the other trees. We still have many shells of the insects, but I will keep treating the tree every February in hopes of saving it. (South Carolina).

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