Scouting for disease: Cytospora canker
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Cause: Cytospora kunzei (fungus) (view photos)
Hosts: The primary host is Colorado (blue) spruce. Other
spruces, Douglas-fir, balsam fir, red and white pines, hemlock and larch
are infrequently attacked.
Symptoms: Wood under the cankered areas of the bark is dark and resin-soaked, compared with light-colored, healthy tissue.
How it’s spread: The fungus overwinters in twig and branch
cankers. Spores released from fruiting bodies during the growing season
infect other branches, particularly at wound sites. Trees 15 to 20 years
old (or older) suffering from drought, compaction or poor site
conditions are prime targets. Trees aren’t usually killed outright, but
the loss of major branches destroys the ornamental value of the tree.
Management: Improve tree vigor; a layer of mulch around the
base retains moisture and helps protect lower branches from wounding by
lawnmowers. Keep trees watered during drought periods. Prune out
diseased branches when the foliage and wood is dry; clean tools with
bleach or other disinfectant after cutting out diseased wood and before
cutting healthy tissue.