Botryosphaeria canker of spruce

Micro-habitat(s)

Distribution

British Columbia

It is widespread but spotty or localized throughout the province. In one area near Wells Gray Park all trees over several acres are heavily infected, but trees nearby are completely free of the disease. This pattern of occurrence reflects some unknown environmental preconditioning in the areas of heavy infection.

Damage, symptoms and biology

Spruce in British Columbia suffers from fewer bark maladies than most other conifers. Most canker diseases of spruce are caused by native fungi that are rather weak pathogens. These can cause deformations, dieback, growth reductions and occasionally death. Cankers are localized lesions in stems and branches, usually caused by fungi.

This fungus produces perennial swellings of excess outer bark (cork). The fungus progresses longitudinally and radially in the bark, so that the swellings gradually get longer and usually girdle the stem. Round, black fruiting bodies are densely formed in the swellings. Branches have been found in which almost half of the surface area is covered by the fungus.

Botryosphaeria attacks trees of all ages. Small seedlings less than 15 cm high have been found with multiple lesions on stem and branches. Mature trees of Sitka spruce (over 30 m high) may have branches in the crown with very numerous cankers. However, young trees on poor sites are most frequently and most heavily attacked. Branches or trees may die from fungus girdling or attack by secondary agents.

Spread of the fungus is by ascospores forcibly shot from the black fruiting bodies covering the cankers. Although little is known of the infection process, the ascospores are present for most of the year in the perennial fruiting bodies and so could infect during any favourable period throughout the year.