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Cottony Maple Scale

Cottony maple scale insects all over a green stem

Adult females are about 3/16 inch long. They are black, flat, and oval. The 1/4-inch white cottony ovisac, or egg sac, is deposited on bark. Crawlers appear in June and immatures in summer on the underside of leaves. There is one generation a year. Immatures overwinter on twigs. Preferred hosts include maple, elm, hawthorn, dogwood, sycamore, poplar, and linden.

Look for white ovisacs on bark in early spring. During the summer, look on underside of leaves for flat, yellow immatures sucking sap from leaf veins where honeydew and sooty mold are found on the host plant.

Apply dormant oils to bark to kill overwintering nymphs. Horticultural oil or insecticidal soap can be applied to leaves during the summer to control crawlers.