Note that downy mildew is systemic, unlike black spot. This means that just getting rid of affected leaves won’t do the trick.

 

Many of you know we have a big problem with black spot on roses in the PNW but how familiar are you with downy mildew? This other disease can look a lot like black spot to some people. It can also result in unusual symptoms that doesn’t look like familiar diseases. Control tactics for black spot do not work on downy mildew. Generally we try to prevent infection in the first place (as in the nursery) since systemic growth is difficult if not impossible to manage. Sunny sites and space between plants will be helpful in the landscape. https://pnwhandbooks.org/…/rose-rosa-spp-hybrids-downy-mild…