It is not easy to grow what most people consider good tree fruits in Maryland without close management, including carefully timed and repeated chemical spray applications for the multiple insect pests and diseases that are common in our area, including fungal diseases such apple scab.
Growing small fruits like strawberries, blueberries, blackberries and raspberries are much more successful without a lot of work.

In the case of rust disease though, the outlook is good and you don't need to worry or treat. See here: 
https://extension.umn.edu/plant-diseases/cedar-apple-rust#symptoms-on-apple%2C-crabapple%2C-hawthorn-and-other-plants-in-the-rosaceae-family-1173260

While we generally recommend that people avoid using many insecticides, herbicides, and fungicides in their landscapes, you generally need to to get unblemished fruit and clear leaves.
This page can tell you more:
https://extension.umd.edu/resource/fruit-plant-care/, under the "plant and pest problems" headline- press on the dropdown menu to expand.
Click on the 'Home Fruit' portion of this Virginia Pest Management Guide:
https://www.pubs.ext.vt.edu/456/456-018/456-018.html
Spray applications are preventative and start very early in the season as the buds swell and are repeated
in various ways on a schedule so it is too late for this season.

If you choose not to take the chemical spray route (most people don't want to) it is still sometimes possible to get some fruit- you will just need to cut out the bad parts- certainly enough to make a pie or two from a mature tree, and you can leave the rest for wildlife.

Christine