Looks like your roses have powdery mildew, Spaerotheca pannosa var. rosae. The fungus likes humid conditions so inadequate air flow through the plant and any water lingering on the foliage becomes a breeding ground for it. You need to remove all the infected leaves and flower buds and put them in the garbage. Neem oil is one of the best treatments for powdery mildew but there are fungal sprays containing potassium bicarbonate available which are effective. Here’s a good article about powdery mildew on roses: https://www.gardeningknowhow.com/ornamental/flowers/roses/roses-powdery-mildew.htm.
Good luck!!
Thanks for your help!!