Diplocarpon rosae

Diplocarpon rosae is a fungus that causes black spot disease, a serious and widespread ailment affecting roses. This fungal infection manifests as round, black spots, up to 1 cm in diameter with fringed edges, primarily on the leaves.1

When roses are infected, their leaves turn yellow and drop prematurely. Susceptible varieties may defoliate twice during a single growing season, significantly weakening the plant, reducing bloom quality and quantity, and making them vulnerable to canker diseases and winterkill.1

The fungus spreads through spores, which are disseminated by splashing rain, dew, overhead watering, or even gardeners working with wet plants. These spores germinate and infect rose tissue rapidly, leading to new spots and further spore production throughout the growing season. Control measures include applying fungicides, planting resistant rose varieties, and promptly removing infected leaves.1