There are biological products like Serenade you could try. The studies I have seen on it's effectiveness are all over the map though. Baking soda mixed with water or milk has also demonstrated some effectiveness when used regularly. Then there is sulfur. It's generally considered about as effective as the synthetic controls, but there are safety issues in using it both for the applicator and the plant so read the label carefully. Other products such as neem oil can be used preventatively. It is also an insecticide that requires ingestion to work on the insect so is considered 'soft on beneficials' If you use any oil based products, do not use sulfur on the plant. The combo will damage the plant. Part of the 'problem' may simply be the age of the plant. These are annuals and once they have produced a certain amount they age and die. It may just be that it's their time and so are weak to whatever is in the area.

Frank, I have had powdery mildew problems on my cherries. I have found Stylet Oil works very well. Any light mineral oil will work - Sunspray, Saf-T-Side, etc. I never tried milk. My impression is oil works better but milk is also a good method. I don't think there is a dormant spray to help with it, just hit is when it comes. Cherries come from places with cooler summers, the heat gets to them. Scott

Powdery mildew is a rare fungus type in that it doesn't need, or like wet leaves. The spores will actually burst if forced to soak up water. Peeing on the leaves at night may well work as it keeps the leaves wet over night. Then again one might be just as successful spraying the plants with water after sunset. People have long suggested various controls for powdery mildew that seem to work OK for some and not at all for others. Water plus milk, water plus baking soda, water plus oil, water plus soap, water plus... It may be it's the water that actually has the effect on it.

Al, do you ever just sprinkle it on the ground in the spring? Do I have to spray it? I'm cleaning up peony foilage now and there is a lot of dry stuff. These peonies got hailed on 4 times this year and a lot of the top foilage dried up. I have never made a spray out of bordeaux, just sprinkled it on. It came in a package with holes in the top.