At this time of year it is likely to be Woolly aphids or Oyster scale insects. Either way the treatment is the same and ongoing. Small numbers may be wiped off with methylated spirits. The fluffy stuff is a form of wax which stops normal insecticides from getting at the actual insect. So you need to remove the wax and the insect then either drowns in the rain or dries up in the sun!. Larger scale numbers really need the tree to be washed down with an insecticidal soft soap. There is one on the market specifically for fruit trees, Winter Wash I think it is called now. I apply it with a stiffish brush at the end of this month. With a big infection you may have to treat the tree a few times to get rid of it.

Agree with owdboggy on all fronts, though I have one customer whose small crab apple I pollard every year, and who loves the woolly aphids - her tree is full of blue tits, coal tits etc and ladybirds feasting on the aphids inside their protective covering which the tits strip off. After ten years, the tree seems to be still as prolific and healthy.

Aphids are not too bad but Oyster scale.........bad news

Agreed!! Googled this, and found this is a particularly nasty problem in the USA. Does Tugbrethil have any local USA suggestions?