In the homemade solution for Black Spot, it says "then add a drop of bleach free dish soap. The soap will prevent the baking soda from slipping off the leaves." Does that mean any ordinary bar of soap or rather what does dish soap mean? I have a lot of Roses and a lot of Black Spot and Rust and would like to clear the problem. I have used Scotts Ultra Rose Control to no avail and would like to try this solution. Therefore, your help would be much appreciated.
Black Spot on Roses
Certified GKH Gardening Expert
Once black spot has gained a foothold the baking soda treatment will be even less effective than it already is. The only product that I have found that truly stops black spot in its tracks is called Mancozeb. It is available at http://www.rosemania.com , it will leave a yellowish powder residue on the foliage for a while but that is part of how it works. You may need to spray again in 7 to 10 days to be sure you get the BS stopped. The black spots never really go away but the fungus is dead and the new foliage should be clear. No need to prune things way down, even if the bush loses some foliage due to the BS it will grow back once the fungus is under control. If the yellow powdery residue bothers you, you can mix the mancozeb with Immunox fungicide as though each were the only thing being mixed in the tank and spray that mix on the foliage. Still leaves a yellowish powdery residue on the foliage but it is less. Here is a link to an article I wrote here at Gardening Know How for you to check out as well: https://www.gardeningknowhow.com/ornamental/flowers/roses/black-spot-roses.htm