My climbing rose bush has black spot on the leaves. By the time I realized I had a problem and then figured out what it was, almost all my leaves are affected. The rose bush is getting quite tall (over 6 feet). I am concerned that I will have to prune this bush way down. I did spray with baking soda, warm water the other day. Any suggestions?
Roses – Black Spot
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 truly stops black spot in its tracks is called Mancozeb. It is available at http://www.rosemania.com and 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 an article for you to check out as well: https://www.gardeningknowhow.com/ornamental/flowers/roses/black-spot-roses.htm