Last year I bought this plant and soon after I got it home, I noticed a white hard crust coating some of the leaves on the interior. I went back to the nursery and was told it’s powdery mildew. It doesn’t actually look like that, at least not like what I have seen on Beebalm.This gets hard, almost like some kind of frost. I have shown it to a number of gardeners and they all seem stumped, and don’t know what to do. It does seem to be a response to leaves being wet, but I water from the bottom, don’t spray it… I have tried a number of mild solutions and I admit, chemicals, but nothing works. Looking online for what others say about this plant, no one seems to have this problem. I assume it’s something that I do- but what? Boy, I would love to have help with this. Another odd thing is that it does not spread to anything else, (which I feared it might). What do you think?