By Kelsey Deckert, Horticulture agent

NDSU Extension - Burleigh County

In the central part of the state, I have been receiving several calls about “marshmallows” on tree branches. As funny as it sounds to say, that is probably the best description for cottony maple scale! The marshmallow you are seeing is actually the female’s egg sac protruding.

Cottony maple scale affects maples, lindens, dogwoods, elm, hackberry and other hardwoods. The scale lives through the winter as an immature female that is about 1/5 inch long, flat on the surface of twigs and branches. Due to their size and flatness, it is very hard to notice them. They will start to grow in May as temperatures warm. By mid-June, the egg sacs are noticeable. Each sac can contain up to 1,000 eggs, which is crazy to imagine given their size.

The crawlers (babies) hatch in late June to early July and will move to the underside of the leaves to feed. It is at this stage that they are most susceptible to chemical control. The crawlers will feed on leaves, and males will complete their life cycle, becoming tiny winged insects; females are wingless. Males will fly to the females, mate then die. The females will continue to feed throughout the fall and then crawl back to the twigs and branches, where they will attach themselves for the winter.

Typically, cottony maple scale infestations are controlled by natural enemies in our landscape and don’t require treatment. If treatment is warranted, you will want to use a combination of a spray treatment for the crawler stage and a systemic treatment. Crawler spray treatments include horticultural oils, insecticidal soaps, pyrethroids and carbaryl. Systemic treatment would be imidacloprid in the fall or dinotefuran in the spring.

Higher populations can produce sap called honeydew, which is their excrement. This can cause black, sooty mold, resulting in a blackened appearance on leaves, twigs and branches. The sooty mold is mostly harmless. In some severe cases, you will see some premature foliage loss.

For more information about cottony maple scale, contact your local NDSU Extension agent. Find the Extension office for your county at www.ndsu.edu/agriculture/extension/extension-county-offices.

NDSU Agriculture Communication – June 30, 2026

Source: Kelsey Deckert, 701-221-6865, kelsey.j.deckert@ndsu.edu

Editor: Dominic Erickson, 701-231-5546, dominic.erickson@ndsu.edu