Managing Seiridium and Botryosphaeria Canker in Leyland Cypress

Managing Seiridium and Botryosphaeria Canker in Leyland Cypress

Twelve 5-year-old Leyland cypress (7 ft tall) are turning brown at the bottom.

Two Major Canker Diseases

Seiridium Canker (Seiridium unicorne)

• Yellowing/browning of foliage on random branches.
• Numerous thin, elongated, sunken cankers on stems/branches.
• Resin exudation (oozing) from cracks.
• Reddish-brown cambium under ooze.

Botryosphaeria (Bot) Canker (Botryosphaeria dothidea)

• Bright rust-colored dead branches.
• Sunken, girdling cankers at base of dead shoots.
• Little or no resin flow.
• Cankers may extend a foot or more on main trunk.

Both Are Stress-Related

Drought, heat, poor drainage, planting too deep, and mechanical injury predispose trees.

Management (No Fungicide Cure)

1. Prune out dead/diseased branches well below cankers. Disinfect tools (10% bleach or alcohol). Destroy debris.
2. Irrigate deeply every 7–14 days during drought (1 inch water). Mulch beyond drip line.
3. Avoid wounding (mowers, trimmers).
4. Do not over-fertilize (excess nitrogen increases susceptibility).
5. Remove severely affected trees (main trunk cankered).

Key Insight

Infection occurred years ago; symptoms appear only after cankers girdle branches. Fungicides are ineffective at this stage. Prevention via stress reduction is the only long-term strategy.