I have battled fungus, the gray stuff on the leaves, on my dahlias for years. I have sprayed fungicide til it drips and yet it persists. It's like there is a race to blooming versus loosing the plants to fungus. Also on begonias. Is there anything anyone else has used that seems to keep it down. My dahlias are in pots and in the ground, mostly in full sun. We have days of rain, but lots of days of warm sun. Ideas?