Brown/Black spotted Azalea leaves
Two years ago I moved into the family homestead. In my mother's garden, she had planted 3 Azalea bushes. In the 2 years I have been here, the leaves turn spotty brown and black after flowering. I have cut and disposed of diseased branches both years but the fungus(?) keep returning. Could it be the soil or diseased plants and, if so, what can be done to revive them?
Try treating with Neem Oil.
If the disease is persistent it may need to be addressed at the soil level.
Solarization may be necessary to stop the spread of the fungus.
Here are some links for you.