Why are there bumps and galls on my autumn blaze maple?

What you are describing on the autumn blaze maple are likely two different pests. The bumps on the leaves are galls (swelling of the leaf tissue) most likely formed by mites. The galls typically do not adversely affect the health of the plant and the damage is cosmetic only.

The cotton-like substance is from the aptly named cottony maple scale. You might have some lecanium scale as well. Scale insects feed on the sap of stems. In small quantities, they are not much of an immediate threat. However, if their populations are not kept in check, they will lead to decline of the tree. There are several different methods for treatment. If you are in one of our service areas, make an appointment today for a recommended course of action.