Discocaninia canker

Distribution

British Columbia

Discocainia occurs along the coast from Alaska to the state of Washington.

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.

The disease is characterized by fusiform, cankered swellings of mainstems and branches. Although the bark over the canker is killed, it does not slough off. There is increased production of wood around the infection, producing the tapered, flattened swelling. Frequently a dead branchlet is found in the centre of the canker and this is probably the entry point of the fungus.

The disease is commonly found in young trees of overcrowded stands or in unthrifty trees of almost any age. The fungus acts as a natural selective agent in removing poor and weakened trees and also as a natural thinning agent. Very frequently, if the tree is weak, the fungus will eventually spread from the canker into the bark above and below it, killing the tree completely. When this happens, the fungus may produce thousands of apothecia (fruiting bodies) which entirely cover the stem.

The conspicuous black apothecia are approximately 3 mm in diameter. The fungus spreads only by ascospores which are forcibly shot from moistened apothecia. When moist, the apothecia open by an irregular split to expose the whitish spore-producing layer.

Main host(s)

Sitka spruce, western hemlock