Cytospora canker of spruce is the most common and damaging disease of spruces in the East. The causal agent, Leucostoma kunzei, attacks black spruce, Colorado blue spruce, Norway spruce, white spruce, Douglas fir, balsam fir, eastern hemlock, eastern larch, European larch, Japanese larch and eastern white pine.

Symptoms:

The needles on infected spruce branches turn brown in spring or early summer. Copious amounts of white sap exude from cankers on the affected branches and run down the tree. White patches of dry resin on the trunk are characteristic of this disease. Brown needles persist throughout much of the growing season, but drop in winter, leaving bare branches. The infection tends to move up through the tree, as older branches are more susceptible than younger ones. This disease affects mature trees, commonly 15-25 years old and 20 to 40 feet high. Symptoms of cytospora canker are the same on other conifers, with cankers produced on branches and trunks of balsam fir, Douglas fir, eastern larch and, rarely, hemlock. Sap production, however, is less noticeable in these conifers.

Disease Development:

Removing a thin slice of bark in the area where healthy and infected tissue meet will reveal tiny, black fruiting structures. Yellow to orange masses of spores ooze from these structures in tiny tendrils during rainy spring and summer weather and are disseminated by splashing water, wind-driven rain, pruning, and possibly by insects and birds. The fungus generally becomes established in fresh wounds, and overwinters on bark and in cankers.

Disease Management:

• There are no effective chemicals to control this disease.
•  Avoid wounding branches.
•  Early detection and removal of infected branches will reduce the probability of more extensive disease development. Prune out infected branches close to the trunk during dry weather or during winter to reduce disease transmission, disinfecting tools between cuts. Burn infected branches to prevent the release of spores.
•  Trees suffering from drought stress and low fertility are more susceptible to this disease, so provide adequate water and fertilizer. Water the entire root zone deeply- 1 1/2 times farther than the branches extend.
• Control insects and mites--especially spruce gall adelgids and spider mites--to prevent spore transmission.
• Picea omorika is resistant to this disease.
•  Avoid planting Colorado blue spruce, as it is extremely susceptible to cytospora canker.

Adapted from the Ohio State University Extension, 1999