Below are the directions for mixing up a safe spray to treat black spot on roses and discourage aphids and other insects. I use this spray weekly on my roses. I also use it if I see mildew or other fungal type disease on any plant.
I mix all the ingredients in an inexpensive pressure sprayer. These are normally on sale for $12 to $15 dollars.
Plan to spray early in the morning before temperatures reach 80 degrees. I also like to spray on days when no rain is expected so the mixture has time to dry.
Regular use greatly reduces the incidence of black spot. I have also successfully used this spray to combat white flies.
Give it a try in your garden and let me know how it works for you!