Leyland Cypress Diseases: Identifying and Managing Seridium and Botryosphaeria Cankers

Leyland Cypress Diseases: Identifying and Managing Seridium and Botryosphaeria Cankers

Two fungal cankers commonly cause brown branches on Leyland cypress: Seridium canker and Botryosphaeria (Bot) canker. Dr. Jean L. Williams-Woodward, Extension Plant Pathologist, provides the following insights.

Quick Field Identification

Run your hand across newly affected branches. If needles fall off at a touch, it's likely Seridium. If needles stay attached, it's likely Botryosphaeria. This method is nearly 100% accurate.

Why the Difference?

• Botryosphaeria cankers expand to girdle the branch, killing it quickly, so needles remain attached.
• Seridium cankers elongate longitudinally without girdling. Multiple cankers disrupt water flow, causing wilting, yellowing, and needle drop—symptoms that mimic drought stress.

Disease Patterns

• Bot canker often affects one or two branches in a localized area (base, pruning wounds, ice damage).
• Seridium canker appears randomly across the canopy, often triggered by drought or other stress. Infection enters through wounds or lenticels.

Canker Characteristics

• Seridium cankers ooze sap profusely but are shallow. Cutting at the ooze site reveals bright red, sticky tissue beneath the bark.
• Bot canker infects wood rays, creating deep, V-shaped cankers when cut transversely.

Best Control: Irrigation

Irrigating during drought is the most effective control for both cankers, especially Seridium. In field trials, irrigated trees healed around canker sites within 1–2 years and remained healthy 4–5 years later. Greenhouse tests showed Seridium expands three times faster on drought-stressed trees.

What to Do on Infected Trees

1. Prune out brown (dead) branches to improve appearance and reduce fungal inoculum.
2. Irrigate consistently to prevent smaller cankers from expanding.
3. Fungicides are not effective once symptoms appear; infection occurred years earlier. No fungicide has proven effective for prevention, and spraying a large tree every 7 days year-round is impractical.
4. Avoid shearing Leylands into formal hedges; shearing increases stress and canker damage.
5. If a tree is severely affected, remove and replant—Leylands grow fast enough that the loss is barely noticed in a few years.

Botryosphaeria cankers

Botryosphaeria cankers

canker damage on branch