The baking soda mix is said to prevent blackspot, but not to cure it. The best organic cure I know for fungi is milk. Use skim or powdered milk, about 1/3 cup milk to 2/3 cup water. Margaret L Hi, for those who have/had problems with fungis such as blackspot, here's a spay recipe I found on a web page (http://www.countrycaregardens.com/pesticidefreeinsectcontrol.htm): Mix 100 parts water with 1 part baking soda and 1-2 drops dish soap to improve coverage of foliage. For severe disease on tough plants, increase concentration up to 20 parts water to 1 part baking soda. As anyone any idea if this works well or not?? Thanks Jocelyn, Quebec, Canada