Species-specific (Phal equestris) fungus?

[boytjie]

Hello all! Anybody know if there is a fungus that might be specific to Phal equestris? Both my regular equestris and the alba have developed mushy/watery brownish gray areas on the leaves; what's odd is that both plants are not next to each other, and neither of my other two Phal species (bastianii or stuartiana) have picked up whatever this is, even though they're growing closer to the equestris. I've cut off the affected leaves and dusted with cinnamon. Any ideas? I'll toss them out if I have to... Thanks!