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.