I'm in the exact same boat, Jacque! Very frustrated that all of the numerous home remedies failed, and really didn't want to resort to commercial sprays.

Next year, I will start spraying fungicides nice and early before the dratted powdery mildew takes over. The spores are probably all over the soil surfaces from this season, and after digging will be all through it. I doubt treating the tubers will do anything to slow the PM.

Dr. Hammett, an experienced grower from New Zealand, recently wrote this...

"By the time you "see"powdery mildew on the upper surface of leaves you already have a massive infection that is difficult to control. Infection starts on the underside of leaves and goes unnoticed. MBC is the best replacement for Benlate. It is sold in New Zealand as Carbendazim. It is systemic. Spray long before you expect to see infection, so that the pathogen does not get a toe hold."

Thanks CC, I also plan on prophylactic spraying, I guess this is a common problem so until a magic bullet is invented, empathy will have to do!