The Cornell Formula and its various modifications. Some people have also used neem oil and neem-based products. The other choice is to grow only disease resistant varieties. Depending on the rose and your locations, no guarantee that they will be totally successful. If you do some reading up over on the Organic Gardening Forum, especially the FAQ, you'll get more information on how healthy soil helps in disease prevention.

The single most effective means of control for either Black Spot or Powdery Mildew is either a spray made of 1 teaspoon of baking soda in 1 quart of water or a 50/50 mixture of fat free milk and water sprayed every 7 to 10 days to prevent infection or every 5 to 7 days to stop an infection once started. Cornell University does say that Potassium Bicarbonate is more effective that is Sodium Bicarbonate but I have not seen that for sale in the stores so being more effective means little since I cannot buy any. Some people will say you need to add soap or oil or both which is something that I have not done and have seen no need for.

I do not know how long blackspot takes to mutate. I am more familar with people getting a new race (variant, pathotype) of blackspot when they purchase an already diseased rose with a different race (varient, pathotype) of blackspot. Title: Identification of five physiological races of blackspot, Diplocarpon rosas, Wolf on roses Authors: Debener, T.; Drewes-Alvarez, R.; Rockstroh, K. Authors affiliation: Inst. Zierpflanzenzuechtung, Bundesanstalt Zuechtungsforschung, Kulturpflanze, Bornkampsweg 31, D-22926 Ahrensburg, Germany. Published in: Plant Breeding, volumn 117, pages 267-270, (1998). Abstract: "Differentiation into physiological races of Diplocarpon rosae, which causes blackspot on wild and cultivated roses, was investigated with single conidial isolates of the pathogen. Infection experiments with a simple excised leaf assay demonstrated differential interactions between single isolates and a set of 10 test rose genotypes. Differential reactions could be observed among rose varieties as well as between and within a wild rose species. Accordingly, five different physiological races can be identified among the 15 isolates tested. A breeding line and one genotype of the wild species Rosa wichuraiana were found to be resistant against all isolates tested. These data will be employed in further investigations on the genetics of blackspot resistance in roses and for resistance breeding programmes." ----------------------------------------------------------------------------- Title: Response of selected old garden roses to seven isolates of Marssonina rosae in Mississippi Authors: Spencer, James A.; Wood, Opal W. Authors affiliation: Dep. Plant Pathol. Weed Sci., Miss. State Univ., Mississippi State, MS 39762, USA. Published in: Journal of Environmental Horticulture, volumn 10, pages 221-223, (1992). Abstract: "Seven isolates of Marssonina rosae (imperfect stage of Diplocarpon rosae) elicited different blackspot disease expression among 39 Old Garden Roses in laboratory tests. 'Felicite Parmentier' (Alba), 'Mme. Hardy' (Damask), 'The Bishop' (Centifolia) and 'Rosa Mundi' (Gallica) showed no symptoms. 'Cardinal de Richelieu' (Gallica), 'Hermosa' (China) and 'Leda' (Damask) were the most susceptible showing a cultivar ratings mean of 2.86 or more. The Wayne variant was the least virulent, causing susceptible reactions on only 46.1% of the roses. The Hinds variant was the most virulent and caused symptoms of 89.7% of the rose plants tested. The remaining five variants caused disease on 69.1% to 79.5% of the plants." ---------------------------------------------------------------- Title: Occurrence of pathotypes of Diplocarpon rosae on roses in Belgium. Authors: Leus, L.; Kegelaers, G.; Van Bockstaele, E.; Hoefte, M. Authors affiliation: Department of Plant Genetics and Breeding, CLO, 9090, Melle, Belgium. Published in: Plant Protection Science, volumn 38(Special Issue 2), pages 536-538, (2002). Abstract: "Monospore cultures of black spot (Diplocarpon rosae Wolf) were established from isolates collected on outdoor grown roses at different locations in Belgium. These monospore cultures were tested on rose cultivars and species with different levels of natural resistance to examine the possible existence of different pathotypes. For this purpose a screening protocol including scoring after artificial infection was developed on in vitro plantlets. Differences between the examined isolates proved that there exist different pathotypes of Diplocarpon rosae in Belgium."

First, do some research on the available chemical fungicides. If environmental concerns are your top priority, then understand that many chemical fungicides are less damaging to the environment than are many organic ones. Most chemical fungicides are also much less potentially damaging to the person spraying than are even the mildest of insecticides. If you wear proper personal protection at both during mixing and applying, then your risk of contacting enough of the chemical to cause yourself harm is rendered exceedingly minute, and this is for chemicals who have a lower toxicity profile to begin with. I've found that BannerMaxx combined with mancozeb will give you 95-99% control of BS, and this is in a climate much hotter and humid for longer than most, except for Florida. If, after fully informing yourself of the choices available and the consequences of each one of those, you choose organic methods to control disease, be aware that the first principal of organic gardening is to get rid of the disease magnets. That may mean elmininating most of your hybrid teas, as they are not really suited to growing organically in most of the East. Concentrate your energies on the roses that have at least some resistance to disease and your results will be far more pleasing. You must be willing to accept some damage to your roses as a total gardening philosophy. Growing roses organically doesn't mean you just substitute products and achieve the identical spotless results. Also be aware that roses with poorly controlled disease are far weaker going into winter and have a much greater chance of not surviving even mild winters. That again makes your cultivar choices of primary importance. The most effective organic fungicide that I've personally trialed for preventative spraying is horticultural sulpher. It must be applied at least weekly, and during times of rapid growth like in early spring, sometimes twice weekly in order to coat the most rapidly growing foliage. It had an effectiveness rate of 40% in my trial, meaning that Angel Face, a rose that will defoliate 100% with no spraying, will retain 40% of it's foliage if sprayed regularly with sulpher. On a more resistant cultivar, of course the retained foliage % would be higher, but I find ANgel Face a good "lab mouse" with which to judge a spray's effectivity. Sulpher has a tendancy to burn at temps above 86°, which is highly problematic in my location as we regularly have many many summer days with temps above that. None of the baking soda and horticultural oil formulations that you may hear regularly touted had any effectivity approaching even 10%. Neem oil, while a decent enough insecticide, burnt leaves badly and also wasn't terribly effective. Copper is is good, but it burns worse than sulpher and can build up to toxic levels in the soil and is far more dangerous to the human than is sulpher. The more folkloric remedies of milk and cornmeal aren't even worth the bytes...