Milk is more of a temporary cure than an actual preventative. I prefer biological methods because they tend to attack the root of the problem instead of just temporarily changing the pH of the plant surface.
indeed; this article in wine business monthly talks about a multi-pronged approach for an actual preventative, BUT, of the "alternatives," milk and whey outperformed both "horticultural oil" and bacillus subtilis....
i have to admit i'm very very curious about whey, as it hadn't occurred to me as an option until i read this article....
http://www.winebusiness.com/wbm/?go=getArticle&dataId=46910
"The materials that displayed efficacy against PM in greenhouse trials were then evaluated in a series of trials in commercial vineyards. The following is a summary of the results from Verdelho and Syrah vineyards:
The Bacillus subtilis product provided a significantly lower severity of PM infection than the untreated control but was not as effective in reducing disease severity when compared to sulfur, milk or whey. The bacterium performed more poorly in field trials than it did in the greenhouse trials.
Similarly, the potassium bicarbonate material showed efficacy relative to the untreated control in the field, but did not perform as well as sulfur, milk, whey or programs of mixed materials (horticultural oils, potassium bicarbonate, whey and sulfur). And finally, the horticultural oils alone did not perform as well as milk, whey, the combination programs or the potassium bicarbonate.
Clearly, the best performance was seen in the milk and whey materials, with whey being the single most consistent performer. Whey was shown to be effective in a spray concentration of 15 g/L (2 ounces per gallon) when combined with either a surfactant or horticultural oil.
Why whey? Milk and whey convey control for PM through several means. For one, free oxygen radicals are produced when milk or whey are exposed to sunlight. The free radicals destroy the fungal hyphae and conidia. Additionally, a natural antimicrobial compound in milk (lactoferrin) ruptures the fungal conidia."
i've recently been discussing this with one of my gardening gurus and he mentioned something about how the presence of mineral salts in milk are also believed to help inhibit the "grow back".... i always thought milk was a pH thing too, just like baking soda. but apparently there's more to it than that.