Well, you might have infected your neighbor's crabapple! Really, no one can guarantee that for sure. In order for the rust to spread, a host for that particular rust needs to be present. Do you grow anything that might be affected by the same type of rust? Besides that, how do you know which particular rust you have? Here is one link that lists a few strains and what they attack.
Get rid of it. This year, I didn't spray my hollyhocks. They are just about to bloom and they look so bad, I am going to chop them down. |
Here is a link that might be useful: Gymnosporangium rusts
