I tried powdered milk a few times last year. It left blotches on the leaves. Perhaps if you sprayed only the undersides or made it more dilute it would work better. I believe Martha Stewart had instructions on her web site. A friend swears by milk sprays and cornmeal scattered on the ground under her roses. Her garden had an air of "eu de baby vomit", I suspect it was the milk. Her roses still had blackspot and the corn meal looked odd. I decided to use the powdered milk for cappuccino foam instead.
I couldn't find freeze pruf in the local stores, but may try to mail order it.
I read recently about someone making their own dormant oil spray using orange rinds soaked in water. Next time I have oranges, I may try it. It would smell much better than sour milk.
