I use Mycostop bio-fungicide, personally, but horticultural oil can be used as a prophylactic. The mycostop is a much better solution in my opinion: Oil really only lasts a week, and is washed off with rain, and then needs to be re-applied for continued protection.
I start by sprinkling some into my rockwool cubes when I transplant clones to larger cubes and also dip the clones in a solution containing the mycostop at that time. A few days before going into flower I like to give the garden another foliar spray containing the mycostop and two weeks into flower I apply a final foliar application for good measure. I live near the coast so humidity is high so I need to stay vigilant with my IPM strategies.
What do you know about jadam? Or KNF? And things like horse tail , stinging nettle, yellow dock, and ginger and garlic there’s something I want to try that I haven’t gotten around to yet is a yellow onion ferment I might make it a vinager anyways onions have this high antifungal properties