I have been trying to find way's to use what I have in the kitchen to help our garden plants...and I have found that I can use a mixture of baking soda to control black-spot and powdery mildew.
1 tablespoon of baking soda
1 gallon of water
1 teaspoon liquid dish soap (cheap)
I mix this together and put in a spray bottle.
I use this once a week. * Don't use on a sunny day*
You can use this on strawberries and roses