Where are you located? What kind of tree is that? Are other trees and plants affected? My first impression from most of your photos was white flies, which are big trouble in my experience. But the second and last photos look more like wooly aphids to me. They don't usually cause a lot of damage and are usually only attracted to a single species, unlike white flies. You might google images of each pest to compare.

After googling it, it's not wooly aphid, and I don't think it's white fly. Arkansas, and I'll try to ID the tree next time I'm over there.

Can you contact a local county extension office or university horticultural program to ask what pests are in your area? I would be pretty nervous about putting my plants near those guys too. If they are confined to one tree (or kind of tree), you may want to consider removing it. In my experience, plants aren't often overwhelmed by a pest like that unless they are already weakened by other things like disease. Sorry I can't offer more specific advice. It's best to find out what they are before using any pesticide.