Black spot is a nagging disease of roses. The best way to manage it is with resistant varieties. Your roses seem to be especially susceptible. This will require spraying on a regular basis, perhaps every couple of weeks from spring to mid fall, depending on the weather. I suggest trying products with one of the following ingredients: tebuconazole (Bayer Advanced Disease Control), myclobutanil (Spectracide Immunox), propiconazole (Banner and several others).
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