I had roses on my old garden (northeast light) and could keep mildew under control enough to get good blooms, but in my new garden in south west light, all of a sudden I've noticed all my roses have black spot. I always buy for disease resistance and have different kinds from David Austin roses to climbing to a vigorous himalayan that was started from a twig given to me and has covered half an arbour in two years. In my old garden blackspot wasn't a huge issue, more often mildew, but is this happening in general this spring in other gardens? And if so, why? The different roses are in different locations with slightly different conditions, so the constant factor must be something else.
The constant is genetic susceptibility. I avoid it by planting only kinds that don't get it. One variable is that downy mildew is misidentified as blackspot. 'Paul's Himalayan Musk', if that happens to be the one you referred to, always gets downy mildew in my experience.