I'm gonna' shoot from the hip here. My knowledge of fungicides is really out of date. Until recently(so it seems to me, hahaha) fungicides were applied as preventive measures. They had no curative value. Once you had the disease and the fungus, you had it. I think the curative fungicides are mis-named. While they are absorbed into the plant, they still need to be applied before or just days after the disease is observed. The sulfers, coppers, -zebs &-zates, are all preventive. If you have 'it,' they won't help. If you don't see 'it,' get going now. If you're a little ahead of the problem, the 'curratives' might work. But, since you're here asking, well, it might be too late?
I dunno. Fungicides and their use is a complicated subject. I'm sure my knowledge is way out of date? If only there was a glyphosate-like fungicide!~