Symptoms
Black to dark-brown spots with ragged margins on rose leaves, surrounded by yellowing of the leaf blade. Infected leaves drop in large numbers, weakening the plant and reducing flowering. The disease intensifies in wet seasons and where air circulation is poor.
Treatment
Remove and destroy infected and fallen leaves (the source of infection for the following year), and apply fungicides in cases of heavy infection. Thinning cuts improve air movement through the shrub.
Prevention
Choose resistant varieties, plant with airy spacing, water at the base in the morning, rake up leaves in autumn, and use potassium-rich feeding to strengthen tissues.
Sources
- Growing roses
