Cytospora Canker of Spruce

Causal Agent

• The disease is caused by the Cytospora kunzei var. piceae fungus. The fungus is also referred to as Valsa kunzei var. piceae. The fungal spores or conidia are spread to healthy trees through splashing watering, improper pruning with infected tools and by birds and insects. Tree wounds are frequently entry sites for the fungus. Cytospora canker is commonly seen on the more mature trees that are 15-year-old.

Symptoms

• Dead lower branches and browning needles are usually the first sign of infection. The dead needles may stay on the branch. With disease progression, needles and branch damage moves upwards in the tree. There are cankers on the bases of branches located near the main trunk and on the trunk itself. Trunk cankers girdle and kill the more susceptible tree species. Cankers start to exude a resin that dries in white patches. Removal of bark reveals dead inner bark and brown cambial tissue.

Favorable Conditions

• Spruce trees that are growing poorly are more susceptible to the infection. Trees that are stressed from cultural mismanagement and suffering from drought, mechanical injuries, pest infestation and are inadequately fertilized are also more prone to infection. The fungus rarely attacks trees that are healthy or vigorous. Even when infected, healthy trees usually heal the cankers during spring as soon as new growth starts.

Management

• There are no chemical control options that will cure the disease once a spruce or other tree is infected with the fungus. The best management strategy is to keep trees in good health to prevent the infection from occurring at all. Keep trees well irrigated, watering enough to keep the soil moist to a depth of 1 ½ to 2 feet. Avoid injuring the tree unnecessarily. Keep pests like spruce gall adelgids and spider mites out of trees with timely pest management strategies.