I'm just finding out for myself, but here's somethings that I've read:
Sulfur: I've sprayed with Safer 3 in 1 and it seemed to slow the spread
Copper: I purchased some Liqui-Cop, and will spray this weekend
Streptomycin: An anti-biotic. Seems a little much, but Agri-Mycin is OMRI listed and I might try it for next year
With the exception of Streptomycin, I think most anything that works against fungi will work on BLS. Keep in mind these things work best as a preventative. Once you have a spot on a leaf it's best to remove the leaf, if not the entire plant.