Milk is effective against powdery mildew because the proteins in milk react with sunlight to create an antiseptic effect that kills the fungus. RECIPE: Some recommend mixing one part milk with three parts water, while others recommend a more concentrated 40% milk to 60% water mixture. You can use either whole or skim milk, as the protein is more important than the milk fat. When to apply: Spray the milk on a SUNNY days so the leaves have time to dry out. The sun helps the milk dry quickly and fo