Gossyparia (Eriococcus) spuria

European elm scale. (Photo: Tawny Simisky)
Scientific Name: 
Gossyparia (Eriococcus) spuria
Common Name: 
European Elm Scale (a felt scale)
Growing Degree Days (GDD's): 
1029-1388 GDD's, Base 50F, March 1st Start Date (Source: Cornell Cooperative Extension.)
Host Plant(s) Common Name (Scientific Name): 
Elm (Ulmus spp.)
Redbud (Cercis spp.)
Zelkova (Zelkova spp.)
Insect Description: 

First noted in New York in 1884, this non-native scale is now widespread in North America and is found on native and European elms, but also rarely on hackberry and Zelkova. Adult females are approximately 1/8 inch in length. The females produce a ring of white fibers around their black, oval bodies. They are often found in twig forks or rough/creviced areas of bark. By the end of June, females will lay eggs that hatch into bright yellow crawlers, which will disperse to the midrib and leaf veins on the underside of elm leaves where they will remain to feed. Crawlers are tiny and magnification is necessary to observe. Immatures overwinter in the cracks and crevices of the bark of elm trees, or at the base of buds and twigs. In late winter, males may form tiny white cocoons that look like grains of rice which are found attached to host plant bark. One generation occurs per year. 

Damage to Host: 

This insect can cause yellowing of foliage, premature leaf drop, and eventually dieback on its host. Honeydew and thus sooty mold are produced, particularly in the presence of a large population of this insect. Young trees or those planted under poor site conditions (trees that are otherwise stressed) are most susceptible to damage caused by this insect. 

Monitoring: 

Look for female scales on the bark of twigs and small branches, particularly in forks or crotches. From May throughout the fall, look at the underside of elm leaves (near the leaf veins) using magnification to observe the tiny, yellow-bodied crawler stage. Yellowing leaves, dieback, or stunted growth may indicate the presence of this scale.

Cultural Management: 

Asiatic elms may be less susceptible to this scale insect, and may be considered/selected for planting in an area where this insect has historically been problematic. Native and other introduced elms are considered to be more susceptible. 

Natural Enemies & Biological Control: 

Natural enemies such as parasitic wasps and predatory insects have been reported as successful in managing this insect. At least four species of parasite are listed as associated with the European elm scale on the Invasive Species Compendium (ISC).

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)

Neem oil (NL)

Pyrethrin+sulfur (NL)

Pyriproxyfen (eggs) (L)

Spinetoram+sulfoxaflor (N)

Notes: 

Elms may be sensitive to acephate; read and follow all label instructions for proper use to avoid plant injury.

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: 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".