There's an interesting post on the Australian website ABC rural about a biodynamic winemaker Chris Carpenter of Lark Hill who is using milk and chamomile tea to ward off mildew.
Apparently the season has been so wet that many growers haven't been picking at all but Carpenter says his vines have been relatively unaffected
"There's a protein in milk that feeds good fungi on the vine leaves, and it produces an environment that isn't very hospitable to downy mildew" he's quoted as saying.
I discovered from a quick search on Google the treatment isn't new. It was discovered by a Brazilian scientist Wagner Bettiol who published a paper on it back in 1999. There are more detailed explanations of how to use it here and here on a site called Vine Views.