What is the best way to apply NaHCO3 to squash plants to stop white mildew?
Prior to using your sodium bicarbonate (i.e. baking soda), water your plants thoroughly. Also, test it on a small section of plant to make sure that it doesn't suffer any bad reaction.
Add about 1 tbsp. baking soda to 4 cups of water and 1/2 tsp. of liquid soap (don't use any with bleach). Mix in a spray bottle and mist the infected plants, including the undersides of leaves. Repeat 7-10 days. Spray in the morning or evening.