Ask your local cooperative extension office about them.

It's almost surely cottony maple scale and will be difficult to keep under control except by an ongoing treatment program. Other than that, trying to optimize cultural conditions (water & fertilizer, primarily) will help keep the tree's vitality level high enough to combat the infestation.

Cottony maple scale is in an outbreak phase in parts of southern MI. White cottony masses are covering the undersides of branches and sticky honeydew is raining down to cars and sidewalks below. The heaviest infestations are in counties with a mosquito spray program, apparently because of the suppression of predators and parasites of scale insects. The street trees and front yard trees that receive the most spray are the most heavily infected with scale, while the backyard trees have much less scale.

Soil injections of Merit in the fall or early spring should help suppress cottony maple scale, but don't expect 100 percent control. Trunk injections of imidacloprid in late May and June are another option. Also, spraying with Merit after the crawlers emerge (in late June) should give good control.

Al