i would recomend you use what the agricultural / farming industry use for the same PM problem ..
skimmed milk was used because of the cost in the 3rd world of herbicides/fungicides
grapes suffer PM as well the most widely used treatment is Myclobutanil , Eagle 20ew / systhane 20ew these products cost a lot and are industrial strength
you can buy regular strength products containing the same active ingredients Myclobutanil from regular garden stores "systhane fungus fighter" is one that i have used
there is no better option than Myclobutanil it will kill PM dead in 1 or 2 applications, even when it is severe
peace