Black spot on roses is a serious fungal disease. This disease spreads easily, especially in humid and wet environments. It can spread from plant to plant. The disease starts with irregular black spots on leaves. Black spot may also appear on new shoots and petioles. The spots are often surrounded by yellow. As the disease progresses, the leaves turn yellow and fall off. Roses infected with black spot are weakened, and are susceptible to winter damage or death. Black spot can kill roses if they are left untreated.
Examine rose plants for black spots. The spots may be on leaves, shoots, and petioles. The spots may be irregular in shape and surrounded by yellow leaf tissue.
Remove diseased canes and leaves. Burn or seal cuttings in a plastic bag. Do not use diseased cuttings in compost or in the garden. This will spread the disease.
Use a soaker hose or water by hand. Do not use a sprinkler on roses. Avoid water on the leaves when watering. Black spot is spread by water and wind.
Apply a fungicide to plants at intervals of 7-14 days throughout the growing season. Fungicide may be applied in intervals of 5-7 days in periods of frequent rain. The best time to apply fungicide is in the evening. The sun can cause the fungicide to burn the leaves. Fungicide is available at nurseries and garden centers. Apply as instructed on label.
Rake all foliage debris from roses in the fall. Burn or seal in plastic bags. Black spot fungus can survive the winter on infected leaves and canes.
Spray or dust the roses with an all purpose fungicide or sulfur in the spring before new growth appears. The rate of application will vary with each brand or type of fungicide. Follow label instructions.