Canker disease of spruce
Damage, symptoms and biology
Most cytospora cankers in 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.
Cankers are inconspicuous, with little or no bark deformation. Dying branches are usually the first symptoms, but the infection often spreads to the trunk of the tree where large cankers are produced. A heavy white, sometimes bluish, pitch flow is characteristic of the disease, often producing a solid coat over the cankers, or dripping from the branches.
Trees with stem cankers are almost certain to die eventually, but branch cankers may only produce limited deformation with survival of the tree.
The fungus is spread by spores that ooze from fruiting bodies (pycnidia) that are immersed in the diseased bark. The conidia are dispersed by rain drops and probably also by insect and bird vectors that contact the sticky mass. The fungus also has an airborne ascospore state, but it is rarely found.
The fungus overwinters on cankered areas of the bark.
Spore dispersal depends on humidity, rain, wind and insects. The pathogen begins by forming a mass of hyphae (stroma) in bark killed in the first year. The following year, the pathogen’s expansion into the bark will produce stromata containing shiny pycnidia that line up their ostioles at a central point in the centre of the stroma. When everything is wet, a gelatinous orange tentril, loaded with conidia, is expelled from the central point. Although dispersal can take place throughout the growing season, conidial production is highest in the spring. Conidial germination takes place between 20 and 35°C, although optimal germination and dispersal occur around 27°C. Lastly, perithecia are formed in the mass of hyphae under the bark. They are wineskin-shaped and their long necks converge into a central black disc.
Dispersal occurs mainly from the impact of water drops on the stromata. This explains the gradual upward displacement of the pathogen in the crown.
No control measures are carried out in the forest.
In urban areas, this disease is frequently observed on Colorado blue spruce. Since the pathogen primarily attacks ornamental trees subject to extreme environmental and climatic conditions, watering affected trees is recommended to alleviate water stress. In addition, branches with reddened needles must be cut. Care must be taken to clean pruning shears between each cut to minimize inoculation through cutting tools. Balanced fertilization is also recommended to reinvigorate the tree. Lastly, copper-based fungicides can prevent infection, but application must be repeated after each rain. This operation must be performed by professionals trained in this field.
All exotic and native spruces, as well as certain other conifers, particularly white pine, are attacked. The disease may appear wherever spruce is used for ornamental purposes, but rarely, if ever, occurs in natural spruce forests.
Canadian Forest Service Publications
Information on host(s)
Larches / tamaracks, spruces, tamarack