Cytospora Canker

Disease

High Threat

Affects: Blue spruce, aspen, cottonwood

Photo: Joseph OBrien / USDA Forest Service (CC-BY-3.0-US (Bugwood))

Identification & Biology

Fungal disease causing resinous cankers on branches. In blue spruce, causes progressive branch death from bottom up. Stressed trees (drought, poor site) are most susceptible. May be the #1 reason blue spruce are declining in landscapes.

Current Status

Endemic throughout the region.

States affected:

Colorado Idaho Montana Utah Wyoming

What Homeowners Should Do

Prune infected branches 12 inches below canker during dry weather. Sterilize tools between cuts. Improve tree vigor with proper watering. Consider species diversification away from blue spruce.