Colopha ulmicola

Elm cockscomb gall aphid galls. Photo: Theresa Doherty
Scientific Name: Colopha ulmicola
Common Name: Elm Cockscomb Gall Aphid
Growing Degree Days (GDD's): None available at this time.
Host Plant(s) Common Name (Scientific Name)
American elm (Ulmus americana)
Certain grasses *Alternate hosts.
Red or Slippery elm (Ulmus rubra) *Galls often found on this host.
Insect Description:

These insects are often identified by the type of gall they cause on elm foliage. These galls can be irregular and are not identical, but on average are just under 1 inch in length and approximately 1/4 inch tall and toothed in such a way that they resemble a cockscomb. Newly formed galls can be reddish along the sides and top, but as they age and dry, they become hard and brown. On the side of the gall that faces the underside of the host plant leaf, a long seam may be visible. If the gall is split open from this seam while still fresh, a female aphid and her nymphs may be found. The young will normally exit the gall through this seam and are a pale white color with dark legs and antennae. Elm is the springtime host for this insect, whereas the roots of certain grasses are the summertime host. By early summer, these aphids leave the elm gall and fly to the grasses. Like many aphids, the life cycle of this insect is complex. Late in the season, a different winged form of the species returns to the elm to lay its eggs around buds.
Damage to Host:

Irregular, red-brown galls resembling a cockscomb will be seen jutting out of the surface of the leaf. Although aesthetically displeasing to some, these galls do not significantly impact overall tree health and management is often unnecessary.
Monitoring:

Look for red, toothed, and raised structures protruding from the tops of leaves. 
Cultural Management:

If aesthetically displeasing, remove and destroy leaves found with irregular red-green galls that still contain the aphids before the galls dry and brown and the aphids disperse. 
Natural Enemies & Biological Control:

Unknown at this time.
Chemical Management:

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Beauveria bassiana (NL)

Bifenthrin (NL)

Carbaryl (L)

Chlorantraniliprole (NL)

Chlorpyrifos (N)

Chromobacterium subtsugae (NL)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Cypermethrin (NL)

Dinotefuran (NL)

Emamectin benzoate (L)

Fenpropathrin (NL)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (NL)

Isaria (paecilomyces) fumosoroseus (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Neem oil (NL)

Permethrin (L)

Pymetrozine (NL)

Pyrethrins+piperonyl butoxide (L)

Pyrethrin+sulfur (NL)

Pyriproxyfen (L)

Spinetoram+sulfoxaflor (N)

Tau-fluvalinate (NL)
Notes:

Chemical intervention is rarely needed for this insect. Damage to host plant leaves is primarily aesthetic and typically does not cause harm to the overall health of the plant.

Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), chlorantraniliprole (soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), emamectin benzoate (injection), 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".