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Parks, Forestry & Recreation

Urban Forestry Branch

355 Lesmill Rd Toronto, Ontario, M3B 2W8

Cytospora Canker of Spruce

Forest Health Care

Cytospora canker is one of the most common and damaging diseases of spruces. This stem disease is caused by a fungus Leucocytospora kunzei (syn. Cytospora kunzei). The fungus usually infects trees that are weakened by environmental stress, such as drought and freezing shock. Colorado blue spruce is most commonly affected, but it also attacks other conifers. Infection usually does not begin until trees are at least 10-15 years old.

White resin covering a cankered branch.

Host and Damage

Colorado blue spruce with infected lower branches.

Most susceptible hosts are Colorado blue spruce, Norway spruce, but it also affects black, red and white spruces, Douglas-fir, balsam fir, larches, and red and white pines. Cytospora canker is a stress-related disease. Trees weakened by drought, mechanical injury or planted in unfavorable sites are more susceptible to the disease. The fungus generally enters through wounds. The infection usually starts on the lower branches and spreads upwards as spores of the fungus are dispersed by rain-splash. Needles on infected branches first turn purple, than brown and drop, leaving the infected branches bare. Cankered branches are usually covered with white resin. Black, pinhead-size fruiting bodies or pycnidia in the dead inner bark of infected branches are positive signs of the disease. The disease does not kill the tree instantly. Several years or sometimes decades may pass before the trunk or large limbs are completely girdled. The fungus over-winters in the infected branches.

Cytospora Canker of Spruce 2010

Specific Management Practices for Control of the Cytospora Canker of Spruces:

Avoid stem and bark injuries, since the fungus establishes through wounds. Wounds made by improper pruning of lower branches to open space around the base of the tree are the most common entering points of the fungus. Water your trees thoroughly in extended dry periods. Infected branches cannot be saved. There is no effective chemical control of this disease. Prune and remove affected branches. Infected branches should be pruned back to main stem. Prune only when it is dry to prevent further infections. Pruning tools need to be disinfected between cuts.

General Management Practices to Improve Plant Health

Water your trees during dry spells. Infrequent, but deep soaking preferably during the early morning hours is recommended. Water absorbing roots are located within the first 25 cm of the surface and extend outward further than the height of the tree. Place organic mulch, (e.g. wood chips), or living mulch, (e.g. ground covers) around the tree base to keep the soil moist for longer periods and encourage healthier roots. Avoid any unnecessary excavating, grade changes, soil compaction, root cutting or hard resurfacing around trees as these activities destroy vital roots which may lead to tree decline or death. Refrain from using high levels of salt or herbicides around trees.

Forest Health Care is a holistic approach to tree care that focuses on improving the health of trees in an urban environment. Our objective is a healthy, sustainable urban forest. Trees in urban forests are often stressed by compacted soil, drought, poor planting and pruning techniques, air pollution, road salt, damage from construction and much more. Trees planted in the right sites, and properly maintained, are less likely to suffer and are more resistant to pest problems. Pest problems are managed using a decision making process that considers the following: Identification of the host and the pest. Monitoring of the host and the pest. Selection of the appropriate management strategy. Evaluation of the management plan.

Our focus is on pest management programs that are environmentally, socially and economically sound.

Cytospora Canker of Spruce 2010

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