Black spot can really only be treated with preventative treatment.
Once the spot is on the leaf, the leaf is doomed. Best option at that point is to prune and spray, or else the spot puts off spores that infect the other leaves.
The official "organic" treatment involves bordeaux powder (copper based), which is probably more harmful than most of the real fungicides, and is less effective.
Fungicides should not be harmful to bees. They may be harmful to fish, but again, copper is probably the worst of these, and that's "organic".
Banner Maxx has worked best for me (but as with all fungicides, you shouldn't just use one because of resistance). I use Banner Maxx, Daconil, and Triforine, all together. I spray every 2 weeks if it's rainy. If it is hot and dry, I'll stretch that out to a month.
The Triforine (Rose Pride) can be sprayed weekly. The others can hurt the plant if sprayed too frequently.
I've heard good things about Mancozeb too.
The most important time to spray, is when the leaves are developing, and are soft and reddish. This is especially important if you have an active infection. Spray the preventative treatment on the new developing leaves, and your whole plant won't get defoliated.
Last edited by rlitman; 07-25-2012 at 12:30 PM.