Cytospora Canker

Encyclopedia Article

Image of a spruce tree with Cytospora canker
Spruce tree with Cytospora canker 

Overview of Cytospora canker

Cytospora canker occurs most often on older trees, especially those that are planted in poor sites. Trees weakened by environmental stresses, such as drought, freeze injury, or high temperatures, also are more susceptible to canker diseases. The Cytospora canker fungus may attack many different species of hardwood trees, conifers, and shrubs.

Signs and symptoms of Cytospora canker 

Trees infected with the Cytospora canker fungus typically show scattered branch dieback, often starting on the lower branches or where trunk cankers are formed. A close look at the dead branches usually reveals the presence of sticky white sap in conifers. this resinous sap in response to the infection by the canker fungus. In hardwood trees, sunken discolored areas that enlarge (cankers) develop in trunk and limbs. 

Disease cycle of Cytospora canker

The Cytospora fungus gains entrance into branches or twigs of trees through wounds or branch stubs. Over time, the fungus encircles or girdles branches, causing death. Defoliation and dieback occur in hardwood trees, while in conifers, brown needles can be observed on killed branches, but they eventually fall off, leaving bare branches.

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us

Management of Cytospora canker 

Image of Cytospora canker on a Blue Spruce branch
Cytospora canker on a Blue Spruce branch 

As with many diseases, the best control for Cytospora canker is prevention. Plant trees in a good site, one that is well-drained and allows unrestricted growth as the tree matures. Adding mulch around trees increases overall health in many ways, including reducing competition from turfgrass. If dry conditions occur, water deeply if feasible. Any cultural practice that promotes good tree vigor helps prevent canker diseases.

Pruning out diseased branches is the primary means of treating trees showing symptoms of Cytospora canker. Scout declining trees closely for cankers. Prune at least 4-6 inches below any visible cankers. Some branches may need to be pruned back to the trunk. To minimize spread of the disease, prune only during dry weather. The fungal spores of Cytospora can be easily spread when conditions are wet. Fungicide sprays are generally not effective at controlling canker diseases.

For more information on canker diseases, see the publication  Fungal Cankers of Trees.