I bought a bush of `Hansa' a few months ago. In most places
I've lived, such Rugosas have been trouble-free, but I'm in
zone 8b, in North Florida not far from Gainesville now. Most
of my roses (too many of them still in pots, too many of them
bought as bare-root from Wayside Gardens at 2/3 or 3/4 off
list price as end-of-season closeouts) have had some trouble
with black spot; some were almost defoliated...

Hansa isn't one of them. No sign of black spot, but the leaves
were darkened with what looked like some sort of a rust. I've
been spraying everything every week, alternating Daconil and
Funginex; last time I mixed Peters' 20-20-20 fertilizer with the
Daconil in the hope of a tad extra fungicidal action from the
copper in it (well, the dry stuff looks like Miracid, so I assume
it's got some copper). The old leaves are still spotty, but there
are now some new ones growing that look unblemished so far.
Not much leaf drop. I'll keep up the spraying, as we've started
into a rainy stretch again after a couple mostly-dry weeks. This
climate demands irrigation (I use drippers): you can go months
without using it, but when it's dry here, it's very dry, the nearby
swamps dry out and sometimes catch fire, and you water your
plants or they die.

What gives? Do rugosas just hate this climate, or are they (or
maybe just Hansa: last I checked my Sir Thomas Lipton was
okay) susceptible to other fungal diseases but not black spot?

Mark., 8b, acid sand/clay mix with too much phosphate