Yellow Spots on Apple Tree Leaves
I have a 5-year-old semi dwarf Mcintosh apple tree and it has tons of yellow spots all over the leaves. On the underside of the leaves under the spots, it's kind of furry/fiberous (not sure how to explain it). It turns some of the leaves completely yellow.
Certified GKH Gardening Expert
It sounds like you may have wooly aphids. This article will help you with that: