I have a 30 year old rose (Pink Peace), and of late it has been suffering the Black Spot. Last fall, I cut it back as usual, and poured rose dust over it, then covered it with leaves, just like I always do. Now, it’s back. I have been on several sites, and they recommend a baking soda, or cider vinegar spray. What do you recommend? I don’t want to lose this rose. Please help.
When you say that you cover the plant with leaves, you may also be reintroducing the fungal spores back onto the plant. Make sure that any leaves that are afflicted are promptly removed from the area and don’t put them in your composter.
Black Spot loves moisture, so try watering with a soaker hose, and make sure enough air circulates through the plant with careful pruning. Over the years, the rose might have become “enclosed” by other plants, giving it less sunlight and air, thus making it more susceptible.
Treating with sulfur seems to be the gold standard, so continue to apply it carefully following the instructions.
PS. Generally the baking soda recipe often passed around by gardeners is not very effective; although it does help prevent powdery mildew.
For additional Information:
Government of Nova Scotia Fact Sheet – Common Diseases of Roses
Fine Gardening Magazine – Lime and Sulfur Spray