Eastern red cedar is a host of cedar apple rust. A red cedar within ½ mile of your apple variety can be one of the alternate hosts. (If wind direction is just right, can go up to two miles.) Juniperus spp. is another host. The apple side includes apple trees, crabapples, and hawthornes, which are in the apple family. If you really want a great display of this disease, plant some junipers in close proximity to a hawthorne, LOL. It will add color and texture to the landscape, . While there are fungicides to use to control both apple scab and cedar apple rust, I have never attempted such short term control. If the genus of crab or hawthorne is so necessary in the landscape, it is much more logical to replace the tree with a resistant variety. Much better results working with nature than trying to fight it with chemicals. Remember, success with any landscape is 99% cultural practices, and 1% chance. The most important cultural practice is to PUT THE RIGHT PLANT IN THE RIGHT PLACE. Planting crabs or hawthornes with junipers is a very poor cultural practice, because you will get a problem someday. Unless you use resistant crab and hawthorne varieties.