Although usually a cosmetic issue, severe infestations of Cytospora spp.
are possible. In fact, severe infestations are the number one killer of the Colorado blue spruces, occurring only on spruces not grown in their native range.
The fungus Leucostona kunzei causes Cytospora canker, a stem disease. It appears most frequently on Colorado spruces. Occasionally, it attacks Norway spruces and Douglas fir.
Browning of needles and dying of the lower branches of affected trees are usually the first symptoms of Cytospora canker. As the disease progresses, it spreads to higher branches. Occasionally branches high in the tree are attacked even though lower ones are healthy. In time, affected trees become unsightly and lose their value for ornamental purposes. Needles may drop immediately from infected branches or the needles may discolor and persist. Eventually dry, brittle twigs remain in sharp contrast with unaffected branches.
The development of trunk cankers may result in the girdling and death of affected trees. Cytospora canker is most common on trees over fifteen years old, but may occur on younger trees as well.
Control of Cytospora canker requires that all diseased branches be removed from affected trees. The bark should not be injured unnecessarily, since the fungus may enter through wounds resulting from injuries. When the branches or trunks of affected trees are wet, spores exude from cankers onto the surface of the bark. Pruning at this time should be avoided, since pruning tools may spread spores. Both too much and too little water are stress factors that can weaken spruces. Make sure there is adequate drainage and water the trees during droughts.