Hi Shirley, 

Thank you for reaching out! I am sorry to read about your apple tree; it did look beautiful this spring. 

The best option would be to have a certified arborist come out and look at your tree. They will be able to diagnose any diseases, while also evaluating for any environmental issues. Here is a link to find a professional: https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

At first glance, it looks like your tree may have apple scab. It's difficult to tell exactly from the photos, so again, the arborist would be best for an in-person diagnosis. Apple scab is the most common disease on crabapple trees in Minnesota. Symptoms include leaf loss and dark brown to black spots on the leaves, such as you are experiencing. This is a helpful UMN Extension article on apple scab: https://extension.umn.edu/plant-diseases/apple-scab 

There is a great section on "how to manage apple scab", which includes tips such as cleaning up the leaves in the fall and pruning the tree if necessary. 

I really hope this helps!