Compare to corking or cork spot disease.

Sure looks like classic case of apple maggot. The issue with spraying an insecticide only at petal fall is that it will not provide any decent prevention on apple maggot. In SE WIsconsin where I am at, maggot populations tend to peak in early to mid August.

This year is weird as we are still getting maggots in fairly high numbers. I actually had to spray an insecticide late August to continue prevention on maggot. Latest report from UW-Madison stated that maggots are still high even though it is so late for them. Typically maggot is not an issue after September 1st.

Some apples more prone to apple maggot than others! YES. When I was a boy we lived on the remains of an old apple orchard with standard trees. None were sprayed. Some full of maggot damage every year yet others never or seldom. Apple maggot does have a preference as to variety.

From my experience I find Jonathan very prone to apple maggot. NW Greening seems very resistant. Could be because the skin on NW Greening is very greasy. Maggots seem to hate apples that have a greasy skin.

The nursery I am at grows hundreds of apple trees in #10 containers. They are not sprayed. All bore apples. I found zestar and honeycrisp severely damaged by maggot and coddling moth. Yet next to them were Kindercrisp and Connell Red and they had 90% clean apples. Connell Red also has a very greasy skin.

No evidence of frass or tunneling in the above apples. Apple Maggot Fly is relatively large and showy compared to most fruit flies and can be easily seen on the fruit in season.