Curled apple tree leaves

My apple tree is about 10 feet tall. The leaves are curled, or sort of folded into little taco-shell shapes. Not totally curled, like around an insect, just folded in half. I see very little leaf damage; the damage that is there is brown spots on the leaves, so I figured a magnesium deficiency and gave it some epsom salts. I have clay soil, and there has been a drought,so I thought either too much water when it did rain (there are no yellowing leaves, though), or too little water - but it didn't perk up when we got our monsoons. I've given it bone meal, blood meal, and compost.

Any ideas?