Cytospora spp., Sphaeropsi sapineas, Siroccus conigenus are the only cankers found on spruce at this time. Of the three, Cytospora spp. is the one that does the vast majority of the killing It is the number one killer of the Colorado blue spruces and only occurs on spruces when the trees are not grown in their native range.
The fungus Leucostona kunzei (Cytospora kunzei variety picea) causes Cytospora canker, a stem disease. It appears most frequently on Colorado spruces and Norway spruces. Occasionally, it attacks Koster's blue spruce 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 persist. Eventually dry, brittle twigs remain in sharp contrast with unaffected branches.
The cankers produced are inconspicuous because the affected bark does not noticeably change color or become depressed. Frequently, amber, purplish white or white patches of resin appear on the bark in areas where cankers have formed. What color the resin may be depends on how much air mixes with the resin. Careful removal of a thin outer layer of bark in the area that separates diseased and healthy tissue will reveal tiny, black, pinhead-like fruiting bodies of the fungus in the diseased bark. These fruiting bodies contain minute spores which can be spread by rain, wind, or pruning tools. The development of trunk cankers may result in 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 cut back to the nearest living laterals or to the trunk of 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. Since weakened trees are susceptible to this disease, fertilizing to stimulate vigorous growth may help to combat Cytospora canker. Fertilizing may also stimulate new growth that may fill in small vacant areas in the trees but large dead areas seldom fill back in. Both too much and too little water are stresses that can weaken spruces. Make sure there is adequate drainage and water the trees during droughts. There are no fungicides that effectively control this disease.
Written by James Schuster, Extension Educator, Horticulture, and reviewed by Bruce Paulsrud , Extension Specialist, Pesticide Applicator Training and Plant Pathology, University of Illinois at Urbana-Champaign.