What is this white disease on my Apple tree?

I was reading about something like this from the library

if Im right they are wooly apple aphids under the fluff
if I remember they atart at the roots and as the season gets warmer they travel up the tree

hope this is right my memory isnt what it was

x x

Woolly aphids or American blight (neither part of name is true). They are a kind of aphid which covers itself in a waxy substance. It is waterproof and predator proof. You need to use something which will dissolve the wax. So, if only a few then, methylated spirits on a cotton bud, if a lot then buy a horticultural soft soap spray. Even with this you need to apply it with a brush rather than a spray. You can wash them off with a powered pressure spray, but take care not to damage the bark. It will take a few applications of anything to get rid of them all.