isn't it just potassium bicarbonate? ...the point of which is to raise the pH on the leaf surface so PM won't be able to live there? I tried another brand of that stuff, and it worked... sort of. I know many people here are militantly against any artificial pesticides or herbicides, but if you're in veg, you're by definition growing stuff you won't be ingesting. That's the time to grab some
Eagle 20 and use it according to directions. Knocks the sh*t out of powdery mildew, and it stays gone! Once you're a week or two into flower, you don't want to use it, in spite of the directions saying its safe up to 2 weeks before harvest. At that point,
neem oil, potassium bicarb and even Safer soap all seem to keep it in check. Rotate between them to keep the PM guessing and you should do fine.