This is cottony maple scale. In its overwintering stage, it is brown and flat, but in spring the white cottony egg sac expands looking like tufts of cotton. June through July over 1000 eggs are released from those sacs and are refrred to as crawlers. Treatment for this insect is during that time. The timing is when Queen Anne's lace is blooming. Various insecticides are recommended - Insecticidal soap, malathion, imidachloprid - to name a few. However, since you are in MN, you may need to find what materials are registered for use in your state.