My nothers two dwarf apple trees had fruit this year for the first time but the entire crop was ruined. Every apple had bumps on them and you can find tunnels throughout the apple. When you taste one you get a really bitter taste. It seems to effect the leaves as well turning them brown on their innermost veins. I have attached some pictures of the fruit but do not have a picture of any leaves. This is the first year we had apples on these trees but I made sure to pick up all the fruit around the tree and discard them. Please advise so that we can have a great crop next year!
Mackinac County Michigan
This fruit injury from apple maggot. You can find more information here - https://www.canr.msu.edu/ipm/diseases/apple_maggot
you did the right thing to remove fallen fruit which will remove maggots from the system.
With no pictures of the leaves, I am totally guessing here, but it could be apple scab - a fungal disease common to apples if they are not a variety that is resistant to it. check this link for pictures - https://www.canr.msu.edu/ipm/diseases/apple_scab
For home apple grower sprays where you need to protect against insects, and diseases I recommend this short resource from the University of Kentucky https://plantpathology.ca.uky.edu/files/ppfs-fr-t-18.pdf
Here is a good resource on home fruit tree care - https://ag.purdue.edu/hla/pubs/Midwest_Home_Fruit_Production_Guide_940.pdf
They also have a good resource for pest control --https://www.extension.purdue.edu/extmedia/ID/ID-146-W.pdf