White stuff on my Trees

If you see what looks like puffs of white Cotton on your Maple trees this is a sign of an insect called Scale.
Scale is an insect that overwinters in a hard cover which erupts into that white puff you see in the picture. Unsightly but the real problem is the insect sucks on the plant much like a parasite which weakens your tree.
The best preventative is a systemic drench in the fall or spring but it can be sprayed at the time of outbreak.