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Cytospora canker

Michelle Grabowski and Cynthia Ash Kanner

Back to Diseases of spruce trees in Minnesota

pine tree with white tinged needles

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. 


close up of pine tree branch lacking needles

Photo by M.Grabowski


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.


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