Hey there so there are many treatments for PM. Like you mentioned milk is good something about lactobacillus works very well. Ive heard vinegar as well. Any silcon solution is a great option so a calcium silicate or especially potassium silicate. Theres some products called "pre-vent" and its special towards powdery mildew and botrytis(grey mold). Products that contain sulfur or bicarbonate are good, such as neem oil has sulfur in it and that helps it to attack all the spores and prevent the colony from reproducing. If you do the milk option which is one of the best non chemical methods i would do about a 1 to 10 ratio with your mixture. The bicarbonate option is essentially baking soda highly diluted, in that mix you can also add a very small amount of vegetable/mineral oil to help counteract the sodium. Best of luck. Check out the kis organics cannabis cultivation and science podcast, its got a great episode all on PM. Happy growing and flowering.✌️
