Hi Jon,

Thank you for contacting the UNH Extension Yard & Garden Infoline. My name is Debi Green. I am a Master Gardener volunteer and I am happy to give you some information that may help identify what is going on with your apple tree.

Diagnosing plant damage can be involved and may take some digging (no pun intended, haha). You mentioned you've had some problems with fungus and have been spraying. Can you recall what the leaves looked like before they fell? Clues such as this will help to narrow down the answers more but I will send you several links to help you diagnose the problem.

Here is an excerpt from the link below that describes some leaf and bark symptoms of Black Rot and Frogeye Leaf Spot: 

"The first signs of black rot are small, purple spots appearing on the upper surfaces of leaves and enlarging into circles 1/8 to 1/4 inch in diameter. Leaf margins remain purple, while the centers turn brown, tan, or yellowish brown, giving the lesions a "frogeye" appearance. Multiple small, black pycnidia (pimplelike fruiting bodies of the fungus) may appear in the centers and can be viewed easily using a hand lens.

Infected areas of branches and limbs are reddish brown and are sunken slightly below the level of surrounding healthy bark. These cankers may expand each year, a few eventually reaching several feet in length. The margins of older cankers are slightly raised and lobed, and the bark within their centers usually turns light-colored, loosens, and scales off raggedly. This characteristic is not confined to black rot cankers, so it is not a good diagnostic symptom. Pycnidia form on dead wood of the cankered areas."

https://extension.psu.edu/pome-fruit-disease-black-rot-and-frogeye-leaf-spot

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There is a lot more great information in that link, including the diseases life cycle and mitigation. 

Below is a comprehensive resource in PDF form. Chapters 4 and 5 deal with disease pathology and diagnosing plant damage.

https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource006378_Rep9131.pdf

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Lastly, it might possibly be unrelated to disease at all and may be caused from sunscald or freezing and thawing.

 "Frost/freeze cracks and sunscald—cracks usually occur on the south or west side of a tree. They are caused partly by differential freezing and thawing of water in trees. Consider painting the trunks and large scaffold branches of young trees with white latex paint. Late summer or early fall pruning or fertilizing makes trees more vulnerable to frost cracks and sunscald injury." 

https://extension.umd.edu/resource/growing-apple-and-pear-trees-home-garden/

I hope these links will help you find the answer to your apple tree issue. If you need further assistance or have more questions, please do not hesitate to reach out again.