Disease name: Cytospora canker of spruce
Pathogen name: Cytospora kunzei (syn. Leucocytospora kunzei) (fungus)
Hosts: Cytospora canker of spruce is a common and destructive fungal disease of Colorado blue spruce. Other species of spruce vary in their susceptibility to this disease. Norway and white spruce are considered to be somewhat resistant, but not immune to the disease. Occasionally, it is found on Douglas-fir, hemlock, and larch.
Trees under stress or growing outside their natural range are more prone to the disease.
Cytospora canker most commonly affects trees that are 15 years old or older, but younger trees may become infected in high stress situations.
Infected trees are substantially weakened and damaged, but are not necessarily killed. The disease often damages trees to the point where they are no longer suitable as landscape trees.
Symptoms
Cytospora canker often starts on the lowest branches of the tree and progresses upward over a period of several years. It can also strike random branches throughout the crown of the tree. Infected needles turn yellow and then brown, eventually dropping, leaving dry, brittle twigs and branches.
The fungus enters the trunk through wounds and infects the cambium layer, leaving dead bark. This dead tissue is called a canker. The purplish resin that oozes from the canker quickly dries to a thin, white layer. This conspicuous white resin covers the cankered portion of the branch or trunk, sometimes flowing several feet down the trunk of the tree. This is an important means of diagnosing Cytospora canker. Resin flow, however, can also be associated with other tree injuries and is not exclusively symptomatic of Cytospora canker. Within the cankered area, black, pinhead-size fruiting structures of the fungus can be seen with a microscope or hand lens, and are a positive sign of the disease.
Disease Cycle
The fungus survives long-term as mycelium and spores in diseased stems. The canker grows slowly, eventually circling and killing a twig or branch.
The fungal spores are the principal means by which the disease spreads to other branches, entering through bark wounds and injuries.
Infections occur in cool, wet weather.
Spores are dispersed by splashing rain, wind, sprinklers, pruning tools, and possibly by movement of insects and birds.
Canker development is most severe in trees under stress from drought, insect damage, crowding, nutrient imbalance, and mechanical damage to branches, trunks, or roots. Symptom development becomes more common one or two years following a severe drought.
Management
Cultural Management
Because Cytospora canker is a disease of stressed trees, choosing a planting site that is favorable to the tree’s growth is a good preventative measure.
Minimize stress of established trees by taking care not to injure the root system or compact the surrounding soil. Use a three to four inch layer of organic mulch to retain moisture and reduce soil temperature fluctuations. Water well in dry periods and provide adequate moisture in late fall before the ground freezes.
Infected branches should be removed to improve the appearance and reduce the chances of further spread. Avoid pruning or working around trees when foliage, twigs, and branches are wet because water disperses the fungal spores. Clean tools thoroughly and disinfect after each cut when pruning out diseased wood.
Chemical Management
There is no chemical management of this disease.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For current pesticide recommendations, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org).