Cottony Maple Scale starts off as an unnoticeable, brown scale. In the spring, a white egg sac is developed and holds many crawlers (insect). They become active and feed on the leaves between June and July. The crawler's waste is called honeydew. This is the substance that makes our cars, sidewalks, decks, you name it, sticky in the summer.
Treatment needs to be timed appropriately. Dormant oils can be applied in late fall on the overwintering scale. Insecticides can be applied in late June while the insect is active.