Posted: 16/08/2013 at 07:57
No, David, it's fungal. The spores are airborne. Once it's in situ, it can also be transmitted via the hands, secateurs, etc.
As Bookertoo says, there are sprays that claim to deal with black spot but they're only of use if sprayed preventively - that is, very early in the season, before the spores arrive. Once the spores have settled on the leaves and the symptoms are showing, there's no point spraying. All you can do is remove the affected leaves, destroy them, and keep the ground around the plants clear of any diseased plant material.