Forest & Grassland Health

Aspen Target Canker

Cytospora notastroma Kepley & F.B. Reeves
and other fungi


Aspen target canker in Bonanza Creek Experimental Forest.

Target canker with flaring bark.





Aspen target canker in the Bonanza Creek Experimental Forest.

Aspen target canker with flaring bark.


Current Status & Distribution (2020 Update)

We detected aspen target canker at three additional sites in 2020, for a total of 27 records from the Kenai Peninsula, to Chicken near the Canadian border, and north to the White Range. In contrast to the aspen running canker, it occurs in relatively small, localized pockets. This disease progresses slowly, and individual canker length and breadth is limited by tree response. The cankers are distinctively target-shaped with flaring bark. It takes many years until numerous cankers form on a tree bole and effectively disrupt vascular transport to kill a tree. We have isolated the fungus Cytospora notastroma from these cankers. Cytospora notastroma is a newly described pathogen that has been found to be a contributor to Sudden Aspen Decline in the Rocky Mountains. Further work is needed to determine whether this is the only pathogen involved in aspen target canker in Alaska.

Detection Map

Map of aspen target canker observations in Alaska as of 2019.

Distribution of aspen target canker in Alaska based on plot data and informal geo-referenced observations as of 2019. Modeled aspen distribution was developed by the Forest Health Technology Enterprise Team in 2011 (240m-resolution, presence based on dominant tree species by tree diameter).

Links and Resources

Sudden Aspen Decline in Colorado. USFS. 2008. Forest Health Management Rocky Mountain Region webpage 

Aspen Decline. USFS. webpage