It looks like it could be cedar apple rust, a fungus. Do you have cedars or junipers nearby? They can be anywhere within 4 miles, but if they are within hundreds of feet, it is quite likely. A bad infection makes the fruits commercially valueless, but a few spots on the leaves is ok. It doesn't harm the fruits if you use them right away, and the trees can live on and on. The worst of it is cosmetic.
The best medicine is cutting down every cedar and juniper in a 4 mile radius... Also, mulching well, good soil health, the usual. THere are apple cultivars that are more resistant.
I have it here, and most of our apples go for cider but we do have some good ones. Look up images of "gelatinous spore horns of cedar apple rust galls" I have them on a cedar right now. THey are otherworldly.
Uh this is MO. There isn't a lumber mill big enough stateside to handle that much eastern red cedar LOL. I have one cedar tree in the neighbors yard about 200 ft away. Unfortunately, its in his yard and I can't cut it. If it were in my yard I would cut it in a heart beat and take the log to the saw mill for lumber.
At least I know what it is now and I thank you for the info. Eastern Red cedar grows like a weed here. Its literally everywhere so I am sure that most everyne in this part of the world has to deal with this on their apple trees.
Are there any natural remedies for it?
Location: Southern New England, seaside, avg yearly rainfall 41.91 in, zone 6b
There are things people do, like kaolin clay, but I have never tried any. My formula is good soil health and realistic expectations. Also, if you keep the air flow going through the tree (training a new tree or pruning an already-pruned tree) and remove leaf litter it might help. You can remove the galls if you see them on your own tree, but each gall sends out so many spores that if you miss one, it won't make much difference it seems to me. Also, the other trees outside of your control are not helping.
My other solution is to plant other kinds of trees.
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