Gardenias dying.

[Ena]

I have this problem every year its starts around end of May through October. The gardenias bloom then quickly die, leaves turn yellow, then brown, then curl up and fall off. They have holes in them and on the back a layer of a dusty brown powder like, that you can wipe with your finger. I have lost all my leaves on one side of the house and now it's starting on the other side. I was told spider mites but it looks like fungus. I live in Florida so the possibilities or endless.View attachment 67433View attachment 67434View attachment 67435