What is the best control of powdery mildew on potted petunias in greenhouse
Best Control of Powdery Mildew in Greenhouse
Certified GKH Gardening Expert
I prefer neem oil, as long as you do not apply it is direct sunslight. This will take care of the issue quickly. An alternative would be to spray with a mix of one part peroxide, and three parts water.
Here is an article that will give you many other ways to control insects, fungal/bacterial infections, and many other ways to make these yourself: https://www.gardeningknowhow.com/special/organic/