Leyland Cypress Seiridium Canker: Stress Management, Pruning, No Chemicals

Diagnosis

Brown, no new growth, regional pattern = Seiridium canker. Sunken purple/brown bark patches, resin flow, bright reddish-brown dead twigs, black fruiting dots on cankers.

Cause

Stress (weather, drought, wounding) predisposes. Spores spread by rain splash, pruning tools.

Management (No Chemical Cure)

1. Prune: Infected branches 1" below canker. Sterilize tools between cuts (alcohol or 10% bleach).
2. Destroy debris: Burn/bag.
3. Reduce stress: Water deeply in drought. Avoid wounding.
4. Remove severely affected plants.

Prevention

Plant resistant species (Arizona cypress, 'Green Giant' arborvitae). Space for airflow.

Seiridium is the #1 Leyland killer. Cultural management is the only option.