So, I have been looking high and low for information specific to PM germination and couldn't find it anywhere. I hope I didn't overlook any search sources, and in turn reposting something someone else already said. Since, I have stumbled upon some info from UC Davis. Here is the link.... Control of Powdery Mildew Using the UC Davis Powdery Mildew Risk Index But will focus on this paragraph, Essentially PM, most genetics I am assuming, will not grow at all if one's grow environment does not sustain six consecutive hours of 21-30 degrees for three consecutive days. The full article also shows how to reduce reproduction once an infestation has occurred and more, but spore germination was specifically what I was looking for. Hope this helps.