Black spot is a common fungal disease (Diplocarpon rosae) that causes irregular black spots on rose leaves and stems. Spotting usually begins on the lower leaves and moves upward in the plant. Infected leaves turn yellow and eventually fall off. Severe cases result in complete defoliation. Black spot is prevalent in wet and warm seasons and is spread by splashing water.
To prevent black spot:
• Choose rose varieties that are disease resistant. Note that black spot has many forms, so a plant that is resistant in one geographical area may not be in another.
• Irrigate at ground level and avoid overhead sprinkling.
• Prune out crowded and crossing canes to improve air circulation and foliage drying.
• Use a preventive fungicide according to the directions on the label. Sometimes, alternating between two fungicides prevents the fungus from developing resistance.
Contact your local Cooperative Extension Service office for specific fungicide recommendations.
