The GARDENA gardening expert
Basically, you are taking good care of your roses, G. Family. But as far as the approach against rose rust, sooty mould and mildew, there are only these three possibilities:
From the start, only plant healthy varieties if possible, namely at a location ideal for roses. Where that won’t work or is not desired as is your case – and for good reason - then the optimal airing for the plants must be made through appropriate design of the rose surroundings. This allows them to be able to dry quickly after a rainfall and lowers the infestation rate. Also pay attention that all “mildew catchers” (such as old Phlox varieties, etc.) are not located near the roses. This is not all-prevailing because even dew can be enough for the fungus to spread to all rose leaves.
Here, the only help is regular use of fungicide against these three rose diseases. Pay particular care to the changing of active ingredients so the fungus does not form resistant strains. The active ingredient is listed on the packaging of the fungicide. Therefore, not only change the compound but change the active ingredient as well!