During one of our many treks along Cunningham's Ditch, which runs behind our house and is actually a small creek, we found a small cedar tree growing along the bank. This was a couple of years ago, and it was just a small seedling then, which Romie wanted to relocate to our yard.
It was nicely shaped and I was happy when he came walking back to the house with it. We planted it in the back yard and all was well. Then it started sprouting these orange growths that looked other-worldly. I didn't know if it was caused by an insect or if it was a disease, or just what, but they increased in number and size as time went on. The tree didn't seem to be suffering any, but I was pretty sure it wasn't normal or desirable for it to be sporting such things.
I later found out it was cedar apple rust (Gymnosporangium juniperi-virginianae)and it is a fungus that affects...c'mon, guess! Cedars and apple trees. The fungus overwinters on the cedar tree in the form of galls. When the temperature rises above freezing and wetting occurs, as in spring rains, the gall changes in appearance and releases spores, which will then infect any neighboring apple trees. Unless they're 'Red Delicious' apple trees, which are nearly immune to cedar apple rust.
The fungus can be passed back and forth between the cedars and the apples (also crabapples and junipers), but the apple will never reinfect itself. Apple trees are always infected by nearby cedars. We've got numerous cedars within a mile of our property and of course, our small cedar tree that Romie brought from the ditch bank. You'll see small ones growing along the ditch banks quite a bit here.
In order for apple trees to escape infection (without using fungicide), all cedars should be removed from a two-mile radius of apple trees. For complete protection, make it five miles. We didn't know all this when we planted the little cedar tree, and guess where we planted it? Oh, about twenty feet from our two apple trees. We couldn't have planned that any worse. Or so we at first thought.
Our two apple trees are 'Red Delicious.'