I'm trying Actinovate this year, a bacterium that is supposed to work as a wide spectrum fungicide. I like the fact that it doesn't leave a strong chemical residue and that the fungicide can affect change in places not reached by the spray itself. It's available in one tiny size from Gardeners Supply and in an agricultural size from AM Leonard. I have also used potassium bicarbonate, sold as Green Cure and available through Amazon, and had success with it. Not much hazard with either, if one follows the precautions on the label. I still see signs of both blackspot and powdery mildew almost every summer, but I can respond to it and keep it in check.
I started spraying in February. I had some roses still clinging to last summer's leaves, and I wanted to get ahead of a blackspot problem that hit most of my yellow flowered roses last year. I'm hoping new leaves will stay healthy well into old age. Getting started early can be important because if infection establishes in young leaves, the plant is seriously weakened. It's a little less serious in leaves that approach the end of their natural lives.
Although I spray, I am a strong advocate of removing roses that persistently exprerience health problems. Cultivars prone to disease are best removed since doing so can improve the health of other roses. The first line of defense is resistant varieties. Sadly some of us rosomanes need a second line of defense to fend off flare-ups.
