The kermes oak scale is one of a group of species of scale insects known as kermesids. With the exceptions of Nanokermes pubescens and Allokermes kingii, many of these "gall-like scales" have not been well studied by the scientific community. In the northeast, there are approximately 9 species of kermes scales in 4 different genera (at least 32 species in 5 genera exist in North America) (Turner and Buss, 2018). Female scales, as they age, may have hard-shelled, light beige to almost black bodies that are globular in shape and resemble galls. Scales are 3-6 mm. in diameter. The biology and identity of many of these scales is not well understood. In general, their life cycle may be something like the following, based on what is known for Nanokermes pubescens. Females lay eggs over a month-long period which begins around late-June. Eggs mature and begin to hatch in early July. Crawlers migrate to the cracks in the bark of the trunk to spend the winter. In the spring, nymphs molt and then migrate to new twigs. Settling near leaf axils, they insert piercing-sucking mouthparts to feed. By early June, females swell and mature and may be mistaken for small tan buds or galls. Adult males are found maturing on the trunk. The biology for Allokermes kingii is approximately this: one generation occurs per year with adult females located at the base of leaf petioles, resembling small galls. In July and August, they lay eggs that will hatch in September. First instar nymphs overwinter in bark crevices and mature again in April of the following season. Female nymphs will migrate to new shoots where they will mature by June. If several scales are present on a single shoot, their feeding may kill it. Male nymphs of this species mature on the trunk or debris beneath the tree (Johnson and Lyon, 1991).
Gall-like scale insects are found at crotches and on the bark of twigs on white and red oaks. Honeydew is excreted by these scales, and will build up on surfaces beneath. Black sooty mold may then grow on top of the honeydew. Heavy infestation may result in dead twigs or host plant branches. In some cases, reduced tree growth rate has been observed, as well as mortality from heavy infestations.
Look for round, gall-like scales on new oak twigs or at the base of petioles in June, July, or August when females are swollen and may be the most easy to see. Look for crawlers or males on the trunk of trees over the winter (Nanokermes pubescens). During the growing season, scan leaves or items beneath trees for evidence of honeydew, which will appear shiny or glossy, or black sooty mold growing on top of the honeydew on these objects. If found, look above and nearby for these soft scales or other piercing-sucking insects.
Prune off and destroy heavily infested branches.
Parasitic wasps and predators have been recorded as natural enemies of kermes scales. Homalotylus spp. wasps in the family Encyrtidae have been reared from parasitized male scales. Adult female scales are predated upon by a caterpillar species, Euclemensia bassettella (observed in New York). Lady beetles such as Chilocorus stigma (twice-stabbed lady beetle) have also been observed as predators of first instar immature scales (Johnson and Lyon, 1991). Additionally, green lacewings are also mentioned as potential predators of these scales (Invasive Species Compendium; CABI).
Abamectin (NL)
Acephate (NL) (crawlers)
Acetamiprid (L) (labeled for “soft” or “hard” scales)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL) (labeled for “soft” or “hard” scales)
Cyantraniliprole (NL)
Cyfluthrin (NL) (labeled for “scale insects, crawlers”)
Dinotefuran (NL)
Flonicamid + cyclaniliprole (N) (labeled for “soft” scales)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L) (labeled for “soft” or “armored” scales)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin + sulfur (NL)
Pyriproxyfen (L) (labeled for scales (eggs))
Spinetoram + sulfoxaflor (N)
Kermes oak scales are in the Family Kermesidae. Scales from this family are known to have hard or tough scale covers and resemble galls. Active ingredients listed here are noted to be applicable for “scales” on the MA Department of Agricultural Resources Pesticide Registration Search unless otherwise noted above. Check product labels to be sure they are labeled for use on the pest you wish to manage, on the site or location to which it is to be applied.
When used in nursery settings, chlorpyrifos is for quarantine use only.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), imidacloprid (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
