That’s what I do. It’s worked well.

It shouldn’t. Treat it with the Potassium Bicarbonate and Castile Soap Solution

Remember to remove affected leaves and then spray the remaining leaves. This treatment won’t remove the existing powdery mildew, but should help keep it from spreading.

Yes, you could try preventatively spraying them. I wouldn’t leave it on overnight – it would be harder to get the soap residue off once it’s all dried. The residue is what can burn the leaves. Once it comes into contact with the spores, it seems to do a good job killing them, extended contact isn’t necessary.

I understand how it may be confusing. The contact of the solution with the powdery mildew should kill the spores and then you can wash the solution off. The solution does not need to stay on the leaves, in fact if it stays on the leaves sunlight will burn them and cause damage to the leaves. Generally wetting the leaves isn’t a good idea, but it’s necessary in this case to remove the soap residue. I’ll update the blog post to make it more clear and add some pictures of damaged leaves for reference.