What is Gloomy Scale?
Scale insects are becoming quite the prevalent pests in the urban landscape, with gloomy scale being one of the more common variations. Gloomy scale is an armored scale that thrives in hot, humid environments, particularly in the southeastern United States, from Florida up to Maryland and west to Texas. They primarily target red maples but are also known to target other trees such as hackberry, mulberry, tulip poplar, and other maple species.
Adult female scales are legless and wingless, making them immobile. They secrete a hard gray cover that can blend in with the bark, allowing an infestation to go unnoticed until it becomes quite severe. Gloomy scale nymphs, (commonly referred to as crawlers due to their possession of legs) are less than 1mm in size and are orange. Adult males are smaller than females and will develop legs and wings once again in adulthood.
The Gloomy Scale Lifecycle
Gloomy scales spend the winter burrowed below the protective covering on the bark as adult females. Development resumes in the spring when they begin to lay eggs beneath the shell. The eggs hatch in mid to late spring, and the crawlers disperse to other suitable parts of the tree. Once the crawlers have settled and begun feeding, they secrete the hard gray cover and eventually molt. During molting, the females lose their legs while males redevelop their legs and wings. Males emerge in mid fall to mate with adult females. Gloomy scales undergo one generation per year.
Gloomy scales have a piercing straw-like mouth that they insert into plant cells through the bark, draining the tree of its contents. Heavy infestations can stunt the growth of trees, leading to an overall decline, including branch dieback and potentially the death of the tree.
Urban Susceptibility vs. Rural
Urban trees surrounded by hot surfaces, such as roads and buildings, are more likely to become infested than trees in rural environments. Water availability is reduced in urban climates, coupled with an increase in surface and air temperatures. As tree canopy heat and drought stress increase, gloomy scale infestations flourish. Trees in rural or more vegetative environments with scale infestations may need little to no intervention. These areas provide more water, allowing the tree to remain cool, and natural enemies to gloomy scale, including parasitic wasps, lacewings, lady beetles, and midges.
Intervention Options
A simple method to start with once a gloomy scale infestation is first noticed is to wrap a piece of duct tape, sticky side out, around an infected branch during the crawler stage in May. This will help determine if the scales on the branch are dead or alive, as well as slowing the spread if they are alive. For light to medium infestations, a high-pressure washer may be effective in treating infestations by washing scales and scale covers off bark, reducing the population. Pressure washers should only be used during the dormant season in the winter, and the water pressure shouldn’t be high enough to damage the bark. If an infestation is only on a few branches, those branches should be pruned out.
Natural predators should not be viewed as pests; allowing for a more vegetative landscape can encourage gloomy scale enemies to keep populations low. Chemical options include horticultural oils. Horticultural oil sprays can be used on the affected parts of the tree during the dormant season to kill overwintering adults. Some horticultural oils can be applied during the growing season, but the label should be consulted for any chemicals used to avoid damaging buds. Foliar insecticide treatments should be used during the crawler stage in May and June for the best control. Using broad-spectrum contact insecticides such as pyrethroids may be counterproductive, as it could kill off natural predators. Soil injection or drenching using a product with the base ingredient of dinotefuran can provide effective, season-long control as it is a systemic treatment that gets absorbed by the tree.
When To Treat An Infestation
Treating a gloomy scale infestation effectively requires precise timing. The ideal time to treat is during the crawler stage in mid to late spring, which corresponds to specific growing degree days (GDD). GDD is a measure of heat accumulation used to predict the development stages of plants and insects. For gloomy scales, treatments are best initiated when 800-1,200 GDD have accumulated, a period when crawlers are actively dispersing and most vulnerable to interventions.
Achieving control over gloomy scale infestations typically requires a sustained approach, often involving 3-4 yearly treatments. Consistent treatments over several years are crucial because gloomy scales can persist and re-establish from untreated populations or neighboring infested trees, making a single treatment insufficient for long-term control.
Contact the Professionals
While gloomy scale is an easy pest to treat, proper timing is crucial, so catching it early and planning ahead for the proper treatment window is important. Call Barren Tree Solutions for more information on scale treatments, and schedule a free estimate with our ISA Certified Arborist.