Cedar Apple Rust is primarily a disease of apple trees, both crab apple and the edible fruit, but an eastern red cedar or juniper is needed in the area for the tree to be infected. This is because it is a rust disease which needs two host plants to complete the life cycle.
The symptoms on an apple tree are pale yellow spots on the top of the leaf that enlarge and turn orange. The leaf becomes deformed as a little cup is created under the spot. At the bottom of the cups small "roots" eventually develop that are dusty in nature. These dusty particles are the "spores" that will infect the cedars and junipers. Finally, leaves begin to drop off the tree. This is the stage we are at right now in mid to late July. During August the cedars and junipers will be infected and thus begin their part in the cycle of this disease.
Cedar Apple Rust can not be controlled on the current seasons' foliage or fruit. The tree has to be sprayed the following spring with an appropriate fungicide. A couple of applications are needed during the time frame of tight flower cluster through first cover.
The only thing that can be done now is to periodically collect the fallen leaves. It's important to do a complete clean up in late autumn when all the leaves have fallen.
Please stop it to see me for the correct spray to correct the problem in your yard!