Extension > Garden > Yard and Garden > Trees and Shrubs > Diseases of spruce trees in Minnesota > Cytospora canker
Cytospora canker
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Photo by M.Grabowski
This disease is caused by the fungus Leucostoma kunzei.
Cytospora canker is an opportunistic pathogen common on trees stressed by drought, winter injury or other factors. In Minnesota this disease is most common on Colorado blue spruce trees although all spruces commonly grown in Minnesota can be infected under the right conditions. Trees are more commonly infected once they are 10 years or older.
Identification
- Needles on one or more branches turn completely brown or purplish brown then fall off.
- Scattered dead branches occur throughout the tree, often starting on the lower branches and then spreading upward.
- Clear to white to bluish-white resin encrusts cankers on infected branches.
Photo by M.Grabowski
Biology
The fungus that causes Cytospora canker can often be found in healthy branches.
Disease begins in response to a wound or stress from insect feeding, snow or ice
damage, drought stress or other factors. A sunken canker forms on infected branches
and is often coated in a thick layer of resin. It may take several years for the
canker to girdle the branch. Once girdled, the branch dies and the needles turn
brown and fall off. The fungus quickly colonizes the dead branch, but rarely grows
into the tree trunk. The tree trunk can be infected through wounds. Dark raised
pimple like spore producing structures form on infected branches and release yellow
tendrils of spores in wet weather. These spores are carried on wind or splashed by
rain to new branches.
Cytospora canker rarely kills spruce trees but it can severely deform them often
making them unsuitable for the landscape.
Management
- Plant Norway or white spruce instead of Colorado blue spruce.
- Reduce stress on spruce trees by watering during periods of drought and mulching the soil beneath the tree.
- Diligently prune out and destroy infected branches during dry weather. It may take two consecutive seasons of pruning to significantly reduce the disease.
