Botryosphaeria Canker: Host Range, Symptoms, and Management

Understanding Botryosphaeria Canker on Woody Ornamentals

The fungus Botryosphaeria causes branch dieback on a vast host range: horsechestnut, redbud, dogwood, beech, walnut, tulip poplar, sweetgum, crabapple, pine, oak, rhododendron, azalea, rose, willow, elm, yew, and many others. Cankers girdle/kill twigs and branches; small black fruiting structures with spores develop in cankers.

Symptoms

• Rough, sunken, dark brown/black areas around wounds/natural bark openings
• Blackened/dark brown wood and pith in affected branches
• Dead bark falling off cankered areas
• Leaf wilting on affected branches as they die
• Cankers enlarging along branch faster than around circumference

Botryosphaeria enters through natural openings (lenticels) or wounds (pruning cuts). Most susceptible: wounded plants under drought stress. Fungus dormant in wood during winter; spores windblown in spring as activity resumes.

Management

• Prune affected branches late in dormancy before bud break. Destroy infected tissue. Disinfest tools between cuts (1:9 bleach:water 10 min + rinse, or 70% alcohol air dry).
• Irrigate to prevent drought stress, especially late summer/autumn.
• Protect from wounding.
• Plant resistant cultivars in drought-prone areas. Rhododendron hybrids with <10% dieback (resistant): Roseum Elegans, English Roseum, Lebar's Red, Cunningham's White, Roseum 2, Boursault.
• Avoid susceptible cultivars in drought-prone/competitive sites. Rhododendron hybrids with >10% dieback (susceptible): Chionoides White, Wissahickon, Anna Rose Whitney, Spring Dawn, Doncaster, Catawbiense Album, Nova Zembla, Sweet Simplicity, Dr. Rutgers, Lady C. Mitford.

Reference

Benson, Daughtry, & Jones 1991. Botryosphaeria dieback in hybrid rhododendron, 1986-1990. Biological and Cultural Tests 6:108.

Integrated Botryosphaeria Management

The disease is fundamentally a stress-weakness interaction: drought-stressed, wounded plants are invaded. Management therefore centers on stress prevention (irrigation, wound protection) and genetic resistance (cultivar selection). Pruning sanitation prevents spread within and between plants. The extensive host range makes this a significant concern in diverse landscapes and nurseries.