Keep in mind, everytime you touch an infected plant or the fan hits it, millions or spores are released into the air. They will settle on other parts of the plant and start "biting in." Think of it like this, when a single spore lands and conditions are optimal, its starts multiplying. Spores pierce the plant tissue and start feeding. This type of fungus propagates rapidly so you've gotta act quick.
Regalia is a great product. Pricey but effective. I use it as part of my IPM by dunking clones and occasional foliar feeds.
Cease also works by competing with the spores and making it inhospitable for them to take hold.
Green Cure will dry up the active spores but if you over spray it will fry your plants as well.
Cannabis growers are divided when it comes to whether powdery mildew is systemic, but what does the science say?
www.medicinalgenomics.com
Powdery Mildew is arguable the most destructive Cannabis pest. It is an obligate biotroph that can remain invisible to a grower.
www.medicinalgenomics.com