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Cytospora Canker

Death of lower branches of Colorado blue spruce typical of Cytospora canker.
Death of lower branches of Colorado blue spruce typical of Cytospora canker.

Brian Hudelson, UW-Madison Plant Pathology, UW-Extension
Revised:  3/11/2012
Item number:  XHT1003

What is Cytospora canker?  Cytospora canker is one of the most common fungal diseases of Colorado blue spruce.  This disease can also affect Norway spruce (and less frequently other spruces) as well as Douglas-fir and balsam fir.  Trees that are 15 years old or older and are at least 20 feet high most typically show symptoms of this disease.

What does Cytospora canker look like?  Cytospora canker usually first appears on lower branches and progresses up the tree.  Individual upper branches may show symptoms as well.  Needles on infected branches turn purple, then brown and die.  Diseased needles eventually fall off and the infected branches die.  Infected branches often produce a bluish-white sap that oozes somewhere along their length.

Where does Cytospora canker come from?  Cytospora canker is caused by the fungus Leucocytospora kunzei (also referred to as Leucostoma kunzei), which survives in infected branches.  Spores of the fungus are spread by wind, rain splash, insects, birds and mammals.

How do I save a tree or shrub with Cytospora canker?  Immediately remove and destroy any diseased branches, by pruning them using the 3-point method of pruning (see University of Wisconsin Garden Facts XHT1014 for details).  Prune only in dry weather.  Between cuts, be sure to clean your pruning shears by dipping them for at least 30 seconds in a 10% bleach solution or 70% alcohol (spray disinfectants that contain at least 70% alcohol can be used).  This will prevent movement of the fungus from branch to branch, or from tree to tree during pruning.  DO NOT attempt to use fungicide treatments to control this disease.

How do I avoid problems with Cytospora canker in the future?  Perhaps the easiest way to avoid Cytospora canker is to avoid planting Colorado blue spruce.  If you do plant blue spruce, allow adequate spacing between trees in new plantings.  For established trees, judiciously prune branches to open the trees’ canopies.  Proper spacing and pruning promote increased airflow, which leads to a less favorable environment for infection and disease development.  In addition, minimize any stress to your trees.  Prevent water stress by avoiding soil compaction, and by making sure there is adequate soil drainage.  During dry periods, water your trees adequately (approximately one inch of water per week) using a soaker or drip hose.  Proper mulching (one to two inches on a heavier, clay soil; three to four inches on a lighter, sandy soil) can help moderate your trees’ moisture levels.  Prevent nutrient stress by properly fertilizing your conifers based on a soil fertility test.  The University of Wisconsin Soil Testing Laboratories (http://uwlab.soils.wisc.edu/) can assist with soil and plant tissue fertility testing.


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Cytospora Canker

A tree with lots of branch dieback from Cytospora canker.
A tree with lots of branch dieback from Cytospora canker.

Cytospora canker is a fungal disease that attacks and kills individual branches of primarily mature spruce trees, in particular the Colorado Blue Spruce. One by one the branches begin to discolor from the bottom of the tree upward until the otherwise striking pyramidal form of the tree is compromised.
Cytospora is caused by the organism Cytospora kunzei (imperfect form) or Valsa kunzei (perfect from). This fungus naturally occurs as a saprophyte on the dead bark of many conifers. The fungus only causes a problem when the health and vigor of the tree has been weakened by other causes such as drought or poor nutrition.
Trees which are susceptible to Cytospora include Black, Colorado Blue, Engelmann, Norway, Oriental, Red and White Spruces; Douglas-fir; Balsam fir; Eastern Hemlock; Eastern, European and Japanese Larch; and Eastern and White Pines. Infection in Wisconsin is most severe on Colorado Blue Spruce where it kills branches and results in excessive resin production.
As previously indicated, initial symptoms appear on the lower branches and progress upward. Occasionally however, symptoms may begin on the upper branches. Affected branches become off-color, taking on a purple cast which later fades to brown as the needles drop.
The fungus overwinters as fruiting bodies on the bark of infected tissue or as vegetative mycelium in cankers. Infection is suspected to occur during late winter and early spring. The site of infection may be natural wounds such as leaf scars or manmade pruning wounds. The spores of the fungus are dispersed to potential host trees through splashing rain.
Close-up of a bleeding branch.
Close-up of a bleeding branch.

The resulting lesions begin at the base of the branch near the branch collar and spread distally along the branch in an elliptical fashion. The cankers are reddish brown and slightly sunken. There is often an excessive amount of resin covering the cankers. Removal of the bark will disclose sapwood which appears normal in color. Upon close examination, one may find tiny, black, pimple-like pycnidia which represent the fruiting structures of the fungus. It is in these black pycnidia that spores are produced which will continue the disease cycle.
Cytospora canker will not result in sudden death of the infected tree but rather, several years or decades will pass before the trunk is girdled and an affected tree will die. Dead twigs may remain on the tree for many years. Typically, trees less than 15-20 years old are not affected. However, the fungus may attack small branches of young seedlings in nursery beds.
Because Cytospora normally attacks trees under stress, it is important to prevent or eliminate any stresses on susceptible trees. Selecting the proper location when planting spruce in the landscape may be the deciding factor as to whether or not a tree will succumb to Cytospora at maturity. Avoid overcrowding and drought. Take precautions not to injure the root system and do not prune except during dry weather. Disinfesting pruning tools in a 10% chlorox solution or 70% alcohol between cuts will prevent the spread or the disease to healthy trees or branches.
– Karen Delahaut, formerly of the University of Wisconsin – Madison 
Photos courtesy of Brian Hudelson, Plant Disease Diagnostics Clinic, UW-Madison  

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Additional Information

  • Cytospora Canker – UW Garden Fact Sheet X1003
  • Cytospora Canker – in the University of Minnesota’s publication M1265 Diseases of Spruce Trees in Minnesota

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