Acanthococcus (formerly Eriococcus) azaleae

Azalea bark scale. Photo: Tawny Simisky
Scientific Name: 
Acanthococcus (formerly Eriococcus) azaleae
Common Name: 
Azalea Bark Scale
Growing Degree Days (GDD's): 
None available at this time.
Host Plant(s) Common Name (Scientific Name): 
Azalea (Rhododendron) 
Hawthorn (Crataegus) 
Japanese andromeda (Pieris japonica)
Poplar (Populus)
Rhododendron (Rhododendron) 
Willow (Salix)
Insect Description: 

Resembles mealybugs but without the waxy strands. The female is dark purple in color and coated with a white-waxy covering. The adult female is approximately 3 mm. long. Males are half the size of females. One generation has been observed annually in CT. Crawlers or immatures are found on the bark of twigs and stems, especially crotches. Up to two generations are reported in more southern states. Overwintering, immature scales mature in the spring and females lay eggs which hatch approximately by the end of June, mid-July. Crawlers move toward branch crotches, bark crevices, or near the leaves. In the southern portion of its range, it is capable of producing two generations per year. 

Damage to Host: 

These scale insects can produce honeydew, leading to the encouragement of sooty mold growth. Feeding damage may cause leaf yellowing and plant dieback, however most infestations of this insect are minor and infrequent. Therefore, chemical management may not be necessary. 

Monitoring: 

On symptomatic plants, look for white, waxy soft scales on the bark (in crevices), branch crotches, or leaf axils.

Cultural Management: 

In light infestations, the scales may be primarily found in the forks of twigs. If possible, prune out and destroy infested twigs. 

Natural Enemies & Biological Control: 

Reportedly parasitized by a chalcid wasp (Coccophagus immaculatus) (Johnson and Lyon, 1991). Select management options that preserve natural enemies, especially if infestations are light. 

Chemical Management: 

For crawlers:

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Buprofezin (NL)

Carbaryl (L)

Chlorpyrifos (N)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Dinotefuran (NL)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Neem oil (NL)

Pyrethrin+sulfur (NL)

Pyriproxyfen (L) (eggs only)

Spinetoram+sulfoxaflor (N)

Notes: 

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.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: https://www.mass.gov/pesticide-product-registration .