Before you spray anything on leaves, the plant should be well hydrated with water.
The fertilizer may of been to strong to use. Oil and soap for a sticker. Could of been a combination of things, hard to tell. If your in a area of the country that is really bad for blackspot, baking soda may not be that effective. But, I do not want to discourage you from experimenting.
The below recipe seems a bit milder. And do not spray on hot days.

Baking Soda Fungicide
Use for Black Spot or White Powdery Mildew

Ingredients needed:

4 Level teaspoons or 1 1/3 tablespoons of Baking Soda
1 teaspoon of Mild Soap (Dawn, Ivory, should be biodegradable with no phosphates)
1 gallon of Water
Mix all ingredients thoroughly and keep agitated. Then spray plants.

I would have skipped the fertilizer. Preventing disease and fertilizing are two different things.

The Cornell group that developed/commercialized the method have commented on the various variations that have been proposed:

http://www.hiagritech.com/pressreleases.htm

There is a tread discussing this at:

http://forums.gardenweb.com/forums/load/rosesorg/msg0623270424848.html?11

Here is a link that might be useful: press release

Thanks Henry, I have never read that article or forum thread.

It was probably the oil. You have to be careful and not spray on sunny days or the oil can burn.

good article but has anyone had any luck with "green cure"

Apparently in Loveland Colorado, Green Cure worked on Blackspot for a consulting rosarian. See:

http://www.greencure.net/testimonials.asp

Here is a link that might be useful: link for above

For the "official" American Rose Society position see:

http://www.prweb.com/releases/greencure/plant_fungicide/prweb3661264.htm

Here is a link that might be useful: link for above