
I had this happen in my own rosebeds once. It baffled me for a while until early one morning I saw a neighborhood dog relieving himself on my rosebush!! I talked to the owner of the dog about it and did not get much of anywhere. So I just washed the rosebush down, pruned out the dead and dieing canes, then placed a tall edging fence around the area out away from the rosebushes. That seemed to do the trick. It could also be that someone was spraying weeds close by and the drift got over onto the rosebush. I have seen that happen before too. Since it is only one side, I suspect it is something like the above.