I have a problem with all my apple trees. They flower very well then towards the middle to end of May, when I look at the small apples, some have a small leaf stuck to the side. When I pull this leaf away, I find a small amount of mushy apple (only a very small amount) and when I wipe this off, there's always a tiny hole, only one in each apple.
It starts with just a few apples but by the time middle or late June comes, over 65% of the apples are affected. A lot of these damaged apples drop but it can take a couple of months and some grow to full size but then show signs of bruising where the hole is.
Certified GKH Gardening Expert
It could be the result of apple maggots or some other types of caterpiller/worm. These articles should help: https://www.gardeningknowhow.com/edible/fruits/apples/apple-maggots.htm