Glamis again, up close

That's a pretty mild case it seems to me. You could try removing the worst leaves and giving it plenty of water and some food. If it gets worse, you could spray. But if that's the worst it gets, I would just try to keep the foliage dry and pick the worst leaves off. Glamis isn't the fastest grower so don't fret.

Fungicide spraying is preventative, not curative. You have to spray BEFORE it gets bad.

After about ten years of growing GC, I would note the following:

1. GC is quite vulnerable to black spot, as mine gets it here where black spot is pretty uncommon and mild, while 95% of my other roses never show a spot.

2. GC doesn't like hard pruning, so take off as little as you can. It forms a nicely shaped plant without much correction needed, just deadhead to keep it blooming.

3. GC has truly nasty prickles--I never go near it without gloves.

If you are in eastern zone 6, you can expect a lot of blackspot on GC and most roses unless you spray preventatively. If you are in Idaho, maybe not.