Subdue fungicide is not available to the public (praise the Lord). We don't think of fungicides as being hazardous to our health, but many of them are exceedingly dangerous. Even many of those available for household use are known to be cancer causing, cholinesterase-inhibiting toxins.

Though it is usually recommended that you obtain verification regarding specific pathogens via lab testing (your Extension service will probably do this), someone might be able to perform a quickie 'surgical procedure' to be certain.

Other than important cultural chores such as pruning the affected branches back to good wood...and then sterilizing your pruning gear afterwards, there is little that you can do. Keep your plants healthy, properly watered, and avoid injury whenever possible (including haphazard pruning). It the disease progresses, you may want to remove the affected plant entirely and dispose of it.

There are some 'resistant' hybrids, I believe. That would certainly be worth looking into.

Here is a link that might be useful: A short fact sheet

OK, here's how brain dead I am. When you said Botryosphaeria, my brain immediately jumped to Rhodies, in which this particular fungus disorder is much more common. I wasn't paying much attention when you said that an azalea was affected.

Azaleas are more likely to become infected with Phomopsis, another systemic disease with some of the same symptoms.

Anyhoo, everything I said about it still follows!

By the way, if you by any chance had a severe cold spell sometime this winter, freeze damage to azaleas can look an awfully lot like a die back disease...one branch at a time turning brown and dieing.