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Cytospora (Leucostoma) Canker of Spruce

June 26, 2007

Cytospora (Leucostoma) canker is one of the most common diseases in Illinois landscapes, definitely the most common we see on spruce. It is found on trees growing in stressful conditions. Although it occurs on young trees, it is more common on trees at least 15 years old.

There are many spruces grown in Illinois. According to Michael Dirr in Manual of Woody Landscape Plants, spruces have shallow, spreading root systems and “prefer a moderately moist, well-drained soil.” Some spruce species are more tolerant of dry conditions than others; but as a whole, spruces do not grow well in hot, dry conditions. Throw in a soil with low organic matter, put the tree in an exposed site (possibly in a new housing development), and you have a stressed tree. Drought stress also predisposes the tree to infection.

Cankers are dead areas on branches or trunks. They may girdle and kill the branch, or they may partially limit movement of water and nutrients. On spruce, a sappy exudate is usually associated with the canker; this sap is a thin layer, not the large blobs found with some insect pests, such as pine shoot moths. The wood under the bark of a tree with Cytospora canker is brown (dead) rather than green or white. The disease infects lower limbs first, slowing moving up the tree, killing branches as it moves: Most trees lose a limb each year to the disease. The image shows a tree that has been affected for several years.

Species affected include mostly Colorado blue and Norway; but other spruce species, as well as Douglas-fir, balsam fir, hemlock, larch, and red and eastern white pine, may have this disease. A U of I fact sheet, “Cytospora or Leucostoma Canker of Spruce,” Report on Plant Disease, no. 604, is available at http://www.ag.uiuc.edu/%7Evista/horticul.htm. Most Illinois Extension offices also have copies.

Managing Cytospora canker involves removing dead branches and trying to improve tree vitality. Do some sleuthing to find out what conditions are stressful to the tree. Correct as many as possible. Fungicides are usually of little value in control of this disease.