Bicarbonate of soda is alkaline, which does little to inhibit
fungus (including mildew). You need an acid. Try vinegar.

I use a chemical fungicide.


Actually mildew is very adverse to an alkaline environment. That is why both
Baking soda and milk work on this disease and why acid rain increases its
prominence. Fot sodium bicarbonate users, forget the soap and use a small box
of Arm and Hammer to a gallon of water. It doesn't work any better than the
milk treatment but avoids the sour milk smell.