How can I control blackspot on my roses?
Blackspot is a common fungal disease of roses. Symptoms of blackspot are circular black spots on the leaves. Infected leaves turn yellow and drop prematurely. Initially, symptoms develop on the lower leaves and gradually move upward. By late summer, severely infected plants may be nearly defoliated.
The blackspot fungus overwinters on fallen leaves and infected canes. Spores are splashed onto newly emerging foliage in spring. Blackspot development is favored by warm, wet weather.
Careful rose selection, cultural practices, and fungicide treatments can be used to control blackspot on roses. Rose varieties differ widely in their susceptibility to blackspot. When purchasing roses, select rose varieties that are resistant to blackspot. When selecting a planting site, choose a site that receives full sun and provides good air movement. Full sun and good air movement promote drying of rose foliage and discourage blackspot infections. Reduce the amount of overwintering fungi by carefully cleaning up the leaf debris in fall. When watering roses, apply water directly to the ground around the plants. Do not wet the foliage. Fungicide applications must begin at the first sign of disease symptoms.