you can get special insecticide for this very problem . if you can see the wool its too late so get it sooner than later .

I'm assuming you mean horse chestnut scale, which does affect Acers - you don't need to do anything at all unless you see them on the wood, and at that point, wipe them off with a cloth very lightly moistened in methylated spirits. Wipe over afterwards with a clean damp cloth to get off any residual meths. Just keep an eye out for any infestation and treat as soon as you notice it - it may not get it at all this year.

If your Acer is in the ground, it doesn't really need any feed other than raking in some Growmore granules around the base in March/April.