Canker Disease of Spruce

Disease Identification

• Spruce trees are susceptible to cytospora canker, a potentially fatal fungal disease that occurs on a wide range of spruce varieties. Norway spruce, white spruce, Serbian spruce and the Colorado blue spruce and its cultivars are among the most affected varieties. The disease also affects hemlocks, larches, Douglas fir and balsam fir but on a less serious level.

Causal Agent

• Cytospora canker is caused by an infection from the Cytospora kunzei var. piceae fungus. The fungus is also referred to as Valsa kunzei var. piceae. Tree wounds are the common entry site for the pathogen. Infection occurs through the spores or the fungal fruiting bodies also called conidia. These spores are spread by careless pruning cuts, splashing water, rain and also by birds and insects.

Symptoms

• The disease is characterized by the browning of needles and death of the lowermost branches of the affected tree. As the fungus spreads through the tree, the branches start to die in the upper portions as well. Infected trees lose aesthetic value as needles start to fall. Brown needles are also likely to stay on tree for extended periods. Cankers on the bark are often inconspicuous at first. Later an amber, purplish white or white resin starts to develop on the cankered sites. Removal of bark reveals black-colored fruiting bodies on infected sapwood.

Management

• The management of cytospora canker focuses on preventative strategies as there are no fungicides to control symptoms once trees are infected. Prune back all the infected branches to the trunk. Avoid pruning healthy trees unnecessarily and minimize damage to tree bark. When pruning infected limbs, make sure the tools are disinfected after each cut. Keep trees in good health with adequate fertilization and irrigation as healthy trees are inherently more defensive towards many diseases.