Can anyone help me identify what is wrong with this apple tree and how to cure it. Most of the leaves have these. Yellow/orange spots on top and growths on the bottom of the leaves under those spots. I took the best pictures I could with my phone's focus. My best guess from research is cedar-rust. There are definitely a lot on the property, but none nearby. Didn't notice this in the spring when I mulched and fertilized.
I'm afraid it is Cedar Apple Rust, the common term used for Gymnosporangium juniperi-virginianae, a fungal infection which requires both apple/crabapple and juniper plants to complete its life cycle. There aren't really an ideal solutions, nothing that will kill it off, so the usual course is to keep a check on Junipers and prune out any galls seen before they get to the orange, gelatinous stage and ready to disperse their spores.
Now you've got it, you will need to carry out preventative measures, such as checking the junipers, possibly even removing them, sweeping up and clearing away any leaf litter from them and the apple trees, using preventive fungicidal sprays, which may give some control. More info here https://www.planetnatural.com/pest-problem-solver/plant-disease/cedar-apple-rust/