I love roses and have creaeted my own "rose kingdom". Unfortunately, recently very often my roses get brown stains. I then take down the foliage which I do not throw onto the compost heave. Nevertheless, the brown stains are back again and again. Even the special rose spray which I bought in a close-by garden centre does not help. What can I do?
Your roses apparently have Diplocarpon rosae, a fungus. When planting the roses, make sure that their location is sunny and that they do not stand to close to each other. This way, the leaves can dry faster which is important as fungus likes humid areas. The soil should be slightly alkaline. If you use fungicides, try to alternate the sprays and especially the active ingredients. This way, you avoid the fungus building up a resistance to the herbicides. In the long run, I would recommend to switch to fungi-resistant rose varieties.