Gloomy scale (an armored scale) is primarily a pest of red maples but has been observed feeding on other tree species including sugar maple, elm, tulip poplar, hackberry, boxelder, buckthorn, sweet gum, mulberry, native hollies, and soapberry. Gloomy scale is found throughout the southeastern United States as far north as Maryland, south to Florida, and west to Texas. They are more abundant on trees in cities than in natural areas. Adult female covers, called tests, are up to 2 millimeters wide with a central pale ring. The test is convex and can be grey to brown and blends in with the bark. Beneath the test the soft-bodied scale insect is pink, legless, and wingless. Males are smaller, have an oval shaped armored covering, and develop legs and wings as an adult. The nymphs, called crawlers, are less than 1mm and orange. The young female nymphs resemble adults but have significantly smaller bodies and armor.
Treatment Strategy
Gloomy Scale is very difficult to manage after the populations have established. Early detection is critical for best management of infested trees. Monitor three to four year old twigs for the gray protective covers of this armored scale insect. Heavily infested branches should be pruned and destroyed.
Other Treatment Practices
- Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
- Adequate water is a key factor in maintaining stress free plants. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize stress.
- Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.
- Cambistat can be also be used to promote tree health and reduce the incidence and severity of stress mediated diseases and insect problems on trees growing in urban areas.
Foliar Spray, Soil Application, or Lower Basal Bark Spray Using Transtect
Trunk Injection Using Transtect Infusible
Foliar Spray Using Proxite + RTSA Horticultural Oil
Foliar Spray Using RTSA Horticultural Oil
Foliar Spray Using Up-Star Gold
Expected Results
Trials performed in 2015 demonstrated excellent results with Transtect as a soil or bark spray. If the tree has been heavily infested with severe decline multiple growing seasons may be needed for tree to recover fully. It is suggested to treat trees annually after heavy infestations.
Signs of Damage
- Dark grey scale covers are most noticeable, look for them in August
- Scales infest only twigs, branches, and bark
- Check under scale covers to ensure living females are beneath
- In June/July nymphs are visible and will settle on bark/twigs
- Beneficial insects on the tree may be a tipoff
- Twig stunting, canopy thinning, early fall color and general dieback are common symptoms
Photo: Eric Honeycutt
Bartlett Tree Experts, Bugwood.org
Photo: Adam Dale
Trees At Risk
- Red maple (Acer rubra)
- Silver maple (Acer sacharinum)
- Boxelder (Acer negundo)
- Catalpa
- Elm (Ulmus spp.)
- Hackberry (Celtis spp.)
- Mulbery (Morus spp.)
- Sycamore (Platanus spp.)
- Native hollies (many species)
Biology
- Overwinter as females.
- Eggs are laid in early spring.
- Crawlers hatch in late May/Early June or a 6-8 week period (8 weeks after full leaf expansion of red maple, 1500-2500GDD).
- One generation per year.
References
North Carolina State University
https://content.ces.ncsu.edu/gloomy-scale-1
University of Minnesota
https://conservancy.umn.edu/bitstream/handle/11299/225470/141GloomyScale.pdf
Journal of Integrated Pest Management, Volume 11, Issue 1, 2020, 24
https://academic.oup.com/jipm/article/11/1/24/6047641
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.
