Black spot is a common fungal disease of roses. It usually appears in spring after warm, damp weather. The first symptoms of black spot are circular black or dark brown spots on the leaves of roses. The leaves ultimately turn yellow and begin to fall off. If left untreated, the plant will weaken and produce fewer and fewer blooms. You can take several measures to cure and control black spot on roses.
Prevention is a key factor in controlling black spot of roses. When watering roses, try to water at ground level so that the foliage doesn't get wet. If you do water from over head, water early in the day so that the leaves have time to dry out before nightfall. Another preventative measure is to plant your rosebushes in sunny areas with good air circulation, which will also promote drying.
Apply a fungicide regularly throughout the growing season to control black spot. Fungicides should be used at regular intervals, usually every seven to 14 days, before symptoms of black spot appear, because they are less effective once the plant is infected. Spray formulation of fungicide with provide better control and protection that dust formulations, because they will stick to the leaves better ensuring more thorough coverage.
Removal of Infected Areas
Taking action as soon as you signs of black spot will greatly improve the outcome of your roses. When only a few leaves are infected remove and burn them, so that the disease doesn't spread to other healthy leaves. Remove and destroy any diseased canes. When the growing season ends in the fall, collect all of the leaves from the infected roses and burn them to help prevent the fungus from overwintering and reappearing in the spring.