Cytospora Canker

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

Need to know: 

  • Most common in older trees. 
  • Infected trees typically show scattered branch dieback that starts on the lower branchers or where trunk cankers are formed. 
  • Cytospora fungus infects through wounds or branch stubs. 
  • Preventative measures can be taken such as planting trees on a good site and adding mulch around trees.  
  • To treat diseased branches should be pruned only during the dry weather.  

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.

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. 

Signs of Cytospora canker 

Microscopic Fungal bodies on sunken areas may be evident upon inspection under the microscope.

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 investigate and confirm if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each state's 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.

Want to submit a sample?  Follow the foliar instructions on the pine/ spruce- conifers page.

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.

Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, the only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.

Last reviewed:
April 2022

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 1, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.