Cankers, sunken dead areas of bark and underlying wood, form on the lower branches of the trees girdling small branches in one or two years and large branches after several years. Resin flows out of the cankers and may drip down on lower branches. Cytospora can infect branches through wounds and branch stubs but does not actively develop a canker unless the tree is stressed by drought. Small fungal structures, in which thousands of spores form, develop in the canker. However, during wet weather, the spores ooze out in long yellowish threads .
Rain splashes the spores to other branches and branch killing proceeds up the tree.
Select the planting site carefully, avoiding drought prone sites. Anticipate the future needs of the mature tree and consider whether the site has the potential of supplying the water requirements of a 50-60' tall specimen. Field and laboratory guide to tree pathology. Schoeneweiss, D. F. 1983. Drought predisposition to Cytospora canker in blue spruce.