Cytospora canker of spruce

A common malady of blue spruce trees in southeast Michigan is a tree disease called Cytospora canker. Trees 20 years of age or older tend to be affected the most. Needles on lower branches will often become yellow, then brown. Often, needles will fall off the tree while still green. After several weeks, infected lower branches will appear defoliated and dead. Usually a bluish-white resin will be observed on branches near the trunk. The presence of bluish-white resin usually indicates cankers beneath the resin.

How to control Cytospora canker

At this point in time there are no documented fungicides available to control Cytospora canker. Control is primarily achieved through proper cultural practices. Avoid tree stress by proper watering during mid summer and deep-root fertilization in the spring or fall. Mulching under spruce trees will help conserve soil moisture in the hotter summer months. The wounding of lower branches by mowers can encourage infection, so mulch rings should be extended to beyond the drip line of the tree.

Branches with resinous cankers will eventually need to be removed. Sterilizing pruning tools between each cut will prevent spreading the disease within the tree or to other spruce trees.