Cedars do effect apple trees but the good news is it isn’t fatal (not a positive for the tree however) and it’s easily controlled with spray. The timing is important, and it’s when the cedar trees produce those orange weird blobs called galls, which is their fruit or seeds or something. It’s when they are out that you need to spray, which is a couple of weeks. Since I have both eating and crab apples and other fruit I’m careful about fireblight and other fungus related diseases so I spray to control it all and don’t have a problem.