To treat Diplocarpon rosae, or black spots on roses, one must remove all infected foliage from the plant and spray with fungicidal soap or sulphur to prevent future infection. One helpful way to ward off black spots is to spray the roses regularly while they are dormant during the Spring.Continue Reading
Black spots are a fungus that form on the foliage of rosebushes. They appear as small dark spots ranging from brown to black and can be distinguished by their frayed edges. If black spots are left untreated, they will eventually turn the rosebush leaves yellow before dropping them to the ground.
Wet, humid and rainy weather tends to bring this fungus out the most as it thrives in moist environments at around 75 degrees Fahrenheit. It only takes around seven hours in these conditions for black spots to germinate, and the symptoms generally show on roses within three to ten days. Every three weeks, more spores are released, making it important to use fungicidal sprays and soaps often. Since black spots can defoliate roses, preventable solutions are recommended over spot treatment. Once leaves show signs of black spots, they should be pruned to avoid the fungus spreading to other areas of the plant.Learn more about Outdoor Plants & Flowers