If you bother to bathe your rose in the morning anyway, I might suggest mixing into a gallon or two of water a few drops of Dawn or your favorite dish detergent, and either potassium bicarbonate - sold online as Green Cure - or two teaspoons of sodium bicarbonate AKA baking soda. If the rose is in a pot, you might tape newspaper over the top and immerse the whole thing upside down in a big can of the mixture.
There are more expensive cures for fungal disease sold at Rosemania, but IMO that way lies madness.
