Here is a disease that we see frequently on spruce trees in Illinois, especially in periods of stress. As we move into hot, dry summer weather, we see more of this canker disease. The pathogen in this case is Leucostoma kunzei, formerly called Cytospora kunzeiValsa kunzei. Cytospora canker and Leucostoma canker are one and the same disease. You will see both names in scientific literature. Old texts still have the Cytospora name, and I still prefer to call it Cytospora canker.
Cytospora canker is probably the most common and damaging infectious disease of spruce in Illinois. Colorado blue and Norway spruces are very susceptible, especially 10- to 20-year-old trees. This disease causes death of branches, usually starting at the base of the tree and moving upward. Occasionally, the affected branches are scattered throughout the tree. Needles may drop early from affected branches or hang on for several months, leaving dry, brittle twigs. An important diagnostic feature to note is that Cytospora causes entire branches to die. A girdling canker forms at the base of the branch, and symptoms show first as a branch tip death. Sometimes, this disease is confused with Rhizosphaera needle cast, but that disease affects older needles first while needles at the tips of branches are symptomless. (Refer to issue no. 3 of this newsletter for details about Rhizosphaera.) Cytospora may continue to spread until all the branches on the tree are dead. Conspicuous patches of white resin commonly form on the bark in cankered areas at the base of dead branches. The diseased tissue is brown under the thin layer of outer bark. Black pinhead-sized fruiting bodies of the fungus (pycnidia) form in the inner bark, often embedded in the resin. These fruiting bodies are very difficult to see, so dont despair if you cannot find them.
Don't be fooled when diagnosing Cytospora canker. The mere presence of dead branches does not confirm the disease. Look for resin (sappy) areas at the base of the dead branches. Then look more closely for the black pycnidia. We have seen so much damage to spruce from environmental stress over the past several years that it is possible that injury has nothing to do with an infectious agent. On the other hand, stressed spruce trees are more susceptible to Cytospora canker, and it is highly likely that the disease will eventually invade the stressed tree as a secondary pathogen.
There are no chemical controls to prevent or eradicate this disease. Remove dead branches as they occur, waiting for dry weather for this pruning. Try to improve tree vitality by watering in drought stress periods. It may help to apply an organic mulch under the full spread of the branches, but not up against the trunk. Mulch helps retain moisture and maintain a more even temperature and moisture environment for the roots. For more information on Cytospora or Leucostoma canker of spruce, consult Report on Plant Disease (RPD), no.604, available on the Extension VISTA Web site or through your Extension office.