Unaspis euonymi

Euonymus scale males (white) and females (brown). Photo: Lisa Ames, University of Georgia, Bugwood.
Scientific Name: Unaspis euonymi
Common Name: Euonymus Scale
Growing Degree Days (GDD's): 35-120 GDD's (dormant), 533–820 GDD's, 1150–1388 GDD's, Base 50F, March 1st Start Date. (Sources: Cornell Cooperative Extension and Robert Childs, UMass Extension.)
Host Plant(s) Common Name (Scientific Name)
Ash (Fraxinus spp)
Bittersweet (Celastrus spp.)
Boxwood (Buxus spp.)
Camellia (Camellia spp.)
Daphne (Daphne spp.)
Eugenia (Eugenia spp.)
Euonymus (Euonymus spp.) *Preferred host. At least 11 species.
Holly (Ilex spp.)
Magnolia (Magnolia spp.)
Maple (Acer spp.)
Mock orange (Philadelphus spp.)
Pachysandra (Pachysandra spp.)
Privet (Ligustrum spp.)
Snowberry (Symphoricarpos spp.)
Insect Description:

The euonymus scale, while most commonly collected on euonymus, will utilize many additional hosts, such as those mentioned above from Miller and Davidson, 2005. This insect can be found in many temperate regions of the world and is thought to have been originally introduced to the United States from Japan or China. The female scale covers are brown in color, while the male scales have white covers. Adult females are approximately 1/8 inch long and oystershell shaped. Crawlers are orange in color. In heavy infestations, plants can appear coated in white, due to the presence of the slightly smaller (than the females) males of the species. Fertilized females overwinter. (Immatures of this species are said to not survive the winter.) Females lay their eggs beneath their dark brown colored cover in the spring. Eggs hatch over a period of 2-3 weeks and crawlers (nymphs) may appear in early June in New England. A second generation of crawlers is observed in mid-July. Adults may be present again in August-September. Two generations per year are thought to occur in New England, but up to three generations per year could occur in southern states. 
Damage to Host:

This insect may be found on the twigs, stem, and leaf surfaces of its hosts. In light infestations, euonymus scales can cause the formation of yellowish or whitish spots on host plant leaves. In heavy infestations, plants can drop their leaves in response to the presence of the euonymus scale. Plantings close to buildings have historically been observed to be more severely impacted by this insect. Dieback of the host plant is reported after 2-3 years of heavy infestation with this species.
Monitoring:

Look for scales on the stem of host plants at ground level. They are well protected in this area and may first be found here. White male euonymus scale covers may be visible on leaves. Wrap black electrical tape (sticky side out) around infested twigs to monitor for the presence of crawlers. Off-color/yellow or white spotted leaves may first be noticed on infested plants. 
Cultural Management:

Euonymus kiautschovicus is thought to be resistant to this insect, even when planted amongst heavily infested and preferred hosts in this genus. Avoid planting species of euonymus that have invasive tendencies and outcompete native plant species. This will also result in avoidance of potential issues with euonymus scale on those hosts.
Natural Enemies & Biological Control:

A classical biological control program against euonymus scale was initiated by the United States Department of Agriculture (USDA-ARS) in the early 1980's, using two predators: Chilocorus kuwanae and Cybocephalus sp. nr. nipponicus. Further work was done by the USDA-APHIS in the 1990's in cooperation with different universities, including the University of Massachusetts. In addition to the species mentioned previously, three aphelinid parasitoids: Coccobius sp. nr. fulvus, Encarsia sp. nr. diaspidicola and Aphytis sp. were introduced at that time. In southern New England, both predators established and C. kuwanae became widespread and sufficiently abundant that it reduced the proportion of landscape euonymus plants with high density euonymus scale infestations.
Chemical Management:

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Buprofezin (NL)

Carbaryl (L)

Chlorpyrifos (N)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Dinotefuran (NL)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Neem oil (NL)

Pyrethrin+sulfur (NL)

Pyriproxyfen (eggs) (L)

Spinetoram+sulfoxaflor (N)
Notes:

Contact insecticides may be most effective on the crawler stage.

Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, 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: September 27, 2024. To check current product registrations in Massachusetts, please visit the MA Department of Agricultural Resources Pesticide Product Registration page and click on "Search Pesticide Products Registered in Massachusetts - Kelly Solutions".