Familytripper,
It sounds as if your apple had powdery mildew. A common problem on appleas, but, as you will now have seen, it won't significantly harm the tree. At this time of year I suggest you simply rake up fallen leaves to reduce the risk of any infection carry over and then, when you do your winter pruning, make sure you prune out any stems showing silvery-white deposits, as these may be overwintering mildew.