Black Spot on Roses*


I have a friend that has never had black spot before on their roses, and this year they have Black Spot. What can you suggest — to treat this condition.


Rose Black Spot is one of the most common diseases of roses. It is caused by a fungus, Diplocarpon rosae, which infects the leaves and greatly reduces plant vigour. This fungal disease causes purple-black spots on leaves that usually yellow and drop. The disease overwinters in infected canes and fallen leaves so it’s important to break the cycle before it begins next year. The article at the link below from the Missouri Botanical Garden outlines the steps to take to bring this fungus under control. Note that as this is a US reference their recommendations regarding the use of fungicides may not apply in Ontario where the cosmetic use of pesticides is banned except in the case of some low-risk products. There are organic fungicides available in Ontario. Check with your local garden centre if you decide to try this approach. The use of any fungicide does present some risk so be sure to follow the instructions on the product carefully. Good luck.

Missouri Botanical Garden: Black Spot of Rose