Prophylactic treatment again powdery mildew

Last year I grew my first garden with a lot of success, except my squash that got wrecked by powdery mildew. There were some conditions I can improve on to make this less of an issue, but it seems like my maple tree has a permanent infection it’s not really bothered by; 50% ish of its leaves dropped this fall and winter have powdery mildew on them. The leaves grow pretty densely but as far as I could tell in the summer the mildew wasn’t visible before they dropped.

How can I treat this preemptively now that all the leaves have dropped? Is there a soil treatment? Spray the bare branches? We don’t use the leaves as mulch and they won’t be present on the ground for 6+ weeks before any vegetables get planted.