Remember those orange spider-looking galls on your junipers early this spring? Now there are brown to orange spots on your apple leaves and fruit. This is cedar-apple rust. The spring galls released spores into the air affecting apple trees. Later the spores return to the cedar trees and overwinter waiting to do their cycle over again.
If the spots are on a large apple tree, it will not kill the tree, however, it will reduce the fruit quality. If the spots are on a small tree, it may defoliate the tree increasing winter injury. The tree showing the fungus now, there is not much to do but to keep the tree watered and fertilized.
The only way to control the disease is to spray with a fungicide before the leaves get affected during early spring when the juniper galls are present. This is sometime before the apple petals drop. Make sure the fungicide or orchard spray you are using will control rust. Some apple trees are resistant to cedar-apple rust like Liberty, Freedom, and Redfree.
If your neighbor has junipers, do not go and cut them down in the dead of night. The spores can travel for miles.