Milk as a Fungicide?

The ornamental rosemary Christmas tree I bought for my wife last year started to show signs of powdery mildew recently. I did my internet research for both the causes and treatment / cures. I was surprised to read some of the bleak forum posts that the only way to cure it is to remove it from the dirt it's in, wash the roots and plant thoroughly and then replant in fresh dirt. Seemed a bit extreme, or maybe I'm just overreacting. After researching topical treatments, I opted not to use anything with bleach in it, as it's an herb we often use in our cooking. Baking soda was going to be my pick until I came across information about using milk. Seemed interesting enough, so I loaded up a spray bottle with 1 part skim milk and 9 parts water. I read about many different proportions, ranging from 1:3 all the way up to 1:9. Figured is 1:9 doesn't give me any results after 3-4 days I'd try a higher concentration. One ray of hope I read is that often times the plant needs to be dried out and the powdery mildew will simply go away. Considering the amount of rain we received a few weeks back, and the fact that some of my larger pots are still drying out, it made sense. Unfortunately, it looks like it's going to be cold again this week, hopefully the sun will be shining bright.