The original Cornell formula does not call for fish oil, or seaweed emulsion. It calls for horticultural oil. Some people substitute this with other oils such as vegetable oil.

Superthrive is a commercial product with undisclosed ingredients that some think works, some think is snake oil. There have been several discussions of it on Gardenweb over time. Not strictly organic in any case.

There seem to be a lot of "Cornell" formulas floating around out there today, but it takes about 0.5 percent solution of baking soda to be effective, and it is the baking soda that is the effective part of the mix. Adding soap or oil simply aids in getting the baking soda onto the leaf surface. 1 teaspoon of baking soda in 1 quart of water with a couple of drops of a light oil or soap is all that is needed. Or I have found a 50/50 mix of fat free milk and water, less simply does not work in my garden and it is easier to mix anyway, 1 cup of milk, 1 cup of water instead of calculating a 10 percent mixture.

Kim & Jay...thanks for the suggestions and help.

I think I'll try the milk this year. I've always just ignored mildew and it finally disappears mostly by July here. Being more attentive to mildew this year is one of my New Year's Resolutions.

Isn't baking soda salty? But I guess you use so little it has no effect on the roses?