Perhaps you mean the famous Cornell formula?

In a gallon of water:

1 Tbs ultralight horticultural oil
4 tsp baking soda
1 tsp mild liquid dish soap

It is used for fungal diseases and seems to be especially effective against powdery mildew.

Paula

The Cornell University formula calls for 2 tablespoons of ultralight horticultural oil and one heaping tablespoon (4 teaspoons) of baking soda. Also, if the oil contains an emulsifier (read the label), then the dish soap isn't needed.

But.....what is horti. oil? Is it available at nurseries?

Yes. Hort oil is bought at nurseries. There are different brands. Sun Oil, Ultra Fine, etc. Volk oil is also a hort oil but a heavier weight one that is best reserved for dormant uses, not sprayed during the growing season. The oils are usually with the organic insecticides as that is their most common use. Any nursery clerk should know what you're asking for if you ask for a hort oil or oil spray.

You can use a light oil such as corn, safflower, cannola, in place of the horticultural oil, if like me you aren't too interested in buying enough hort oil to last 50 years.

My goodness, Kimmsr. What kind of horticultural oil are they pawning off on you folks up there? Our garden centers sell Sunspray oil in a pint-size plastic bottle.

Quarts, I've not seen pints out. Since I would only use about 5 teaspoons a growing season I'm not sure I'd want a pint laying around anyway. Wife always has these light oils.

Oh, that is so good to know, Kimmsr! I have avoided trying the Cornell formula just because I don't want to have more stuff to store. (I'm currently trying the milk solution.) But I always have canola.
K.