Powdery mildew on roses?
This does look like powdery mildew. I am including a link to PWN Handbook section on roses, including a section on powdery mildew, how to identify it, the causes, and how to treat. Some of the treatment options are cultural, like selecting varieties that are resistant in your area, clean up, air flow and so on. Other control options include some sprays that are not necessarily 'nasty chemicals'.
Are your roses in pots (I think I see that in image)? If so, you might be able to provide more air circulation between plants by spreading them out. Be sure to remove infected tissue, bag up and discard the removed tissue as well as any under and around the plants.
Here is the aforementioned link https://pnwhandbooks.org/plantdisease/host-disease/rose-rosa-spp-hybrids-powdery-mildew