It is too late this year to save your apples from blemishes. The best thing you can do is to clean up the fallen leaves and apples so that the problem does not overwinter. I am not sure what type of insect or disease you are dealing with, but perhaps if you sent a photo I would have a better idea. Winter is good time to spray fruit trees with an dormant oil spray if disease is a problem. These sprays should only be used on leaf less deciduous plants when the weather is above freezing and you must read and follow the label directions. Good luck and remember, sometimes ugly apples taste great. Keep growing, Marianne Binetti