Using baking soda and vinegar alone is moderately effective, you would need to add a little soap to help fix the mixture on the plant leaves. Personally, I prefer to use baking soda and neem oil together, it is much more effective, since neem oil is effective against powdery mildew, but also against insects. The neem oil must be mixed with soap to be used, so the soap will bind the baking soda and neem oil to the leaves. If you only use baking soda with vinegar, it will not bind to the leaf and you will lose over 70% in effectiveness. Why don't you sell neem oil? There is a very old product that is used in organic agriculture, it is “Bordeaux mixture", it is a mixture of lime and copper powder, it is an excellent fungicide used by millions of farmers in the world since 19th century, you should talk about it. As I wrote in another comment of another of your videos, as a preventive against powdery mildew, you can also use skimmed milk (10% of skimmed milk mixed with water), it is also used in organic farming in Japan.