Black leg

Black, elongated lesions girdle stems and petioles, eventually killing young shoots in cool, wet conditions. Look for this disease on ornamentals during spring when moisture is high and temperatures favor infection. Improve air circulation through judicious pruning and spacing between plants. Remove infected shoots promptly and destroy all material. Avoid overhead watering to reduce humid conditions. Clean up all fallen leaves.

Prevention works better than treatment for black leg. Choose resistant varieties when they exist, site plants where air moves freely, and maintain good sanitation by removing debris and infected material. When chemical intervention is necessary, timing matters more than product: apply protectants before the infection window, not after symptoms appear.