When neem oil doesn't work for a particular plant disease, my next step is either milk or baking soda. Sometimes one or the other will help.
I just tried milk + baking soda mixed together (diluted with water) on some black mustard plants. Does anyone know if the two will counteract each other? Or any other reason not to do this?
I just did it last night and it rained all day, so I have to do it again.\?