Hi Diane, no ma'am, I haven't. Water stress can force much disease. I read many years ago in both Harkness and LeGrice that it could cause mildew, even in high arid heat. I didn't believe it until I did it. I've also forced quite a few roses to rust by drying them out too far. R. Arkansana rusts terribly where it is indigenous. I grew it in a pot here and had awful rust issues with it. I increased the water and new, rust free foliage erupted all over the plant. As long as I kept the water high, it remained clean. If I let it dry out, the whole plant broke out in rust. I couldn't get Heritage clean. It had rust, black spot and mildew during heat and aridity. I increased the water and new, clean foliage replaced the diseased foliage. Penelope mildews in a client's garden virtually all year. Mildew shouldn't be an issue there due to the lack of humidity. When it begins, it means the sprinkler feeding it is blocked. I clear the area of "companion plants" so Penelope gets the water it needs and the mildew stops.

I have a hybrid Banksiae seedling I was having terrible rust and mildew issues with. I can't/won't spray. I tried watering it more heavily and it clears up and remains healthy. There is a double yellow Banksiae out front which capped a huge stand of golden bamboo. It mildewed and repeated its bloom, all summer long. The other large Banksiae out back gets even more heat and less water, but it doesn't mildew when the one in front does. It has no bamboo or any other plants growing under it. The bamboo robs it of water and transpires tremendous humidity under it, forcing it to mildew. I began watering the area and the mildew subsided. There weren't any changes in the weather while I played with water levels, nor had the plants been fed or sprayed, so it seems the amount of water each received resulted in the fungal attacks improving. Nature appears to use water stress to impair the immune system of the plant to trigger it to slow down, perhaps begin hardening off in preparation for cold weather. The biggest issues occur where the season goes on much longer than the water stress should indicate so the plant needs to continue pushing new growth because there isn't "cold weather" it needs to be preparing for.