I've been using this mix for years now, and I have still yet to have powdery mildew on my marijuana plants. When I was growing in the South my grow rooms would regularly get into the 90%+ humidity range, and as I've lived in Colorado (where powdery mildew is an epidemic) I have still yet to get powdery mildew issues.
This blend of oils will also help to protect against spider mites, aphids, and white flies. The one big thing this spray won't protect against is broad mites, cyclamen mites, and hemp russet mites. Those guys are just to tiny and hard to kill for this to work on them. I have tried and tested it, and they thrived unfortunately. That's why its good to use other things in rotation with this spray in your Integrated Pest Management Program. Biological products like Grandevo can work, as well as products like Green Cleaner. There are so many options on the market today that you can find a great match I'm sure.
The recipe is as follows:
1 - Ounce neem oil (I prefer Ahimsa Neem)
2ml - Lavender essential oil
2ml - Rosemary essential oil
2ml - Thyme essential oil
1 - Drop of polyglyceral oleate (don't let the name scare you, it's made from plants)
Mix this into 1 gallon of water in your favorite sprayer, and apply once per week. Shake this periodically while spraying. If indoors it is always a best practice to apply with the lights off. Outside I would also suggest not to spray this while the sun is blazing either. Outdoors I prefer applying in the evening before the sun is about to go down.
This can be used in all cycles of growth in your marijuana grows, and you should have no issue passing most State mandated tests. I say “most” because there could be some updates after this has been written and I don't want the know it alls on the internet to roast me. As of now though, you should be good, but always check local regulations before the use of any new products.
I also use this on my squash and zucchini to keep powdery mildew at bay. It has served me well to get successful harvests year after year with no powdery mildew issues. It also can help with aphids on your kale, brussel sprouts, etc... I use it once a week for most of the later season and will get harvests that are pest and mold free all the way up to the last frost.
I have personally used this mix for many, many years, and have had nothing but success with it. We advise our customers, consulting clients, and everyone else of this recipe. It's a simple natural way to keep mold at bay, and those damn spider mites away from your organic cannabis plants. This in conjunction with a healthy soil will do wonders for your crops.