4.) Cytospora rarely kills spruce trees, but can badly deform them and damage the look of the tree. Cytospora species have been reported on at least sixty genera of hardwood and conifer trees and pose a serious threat to tree fruit crops (Grove 1935). Cytospora canker is a common disease on spruce trees that are stressed by drought, winter injury or other factors. Prune out and destroy infected branches during dry weather. Cankers kill random branches throughout the tree canopy. (Fig. During the summer of 1929 an even more serious manifestation of Cytospora canker on apple trees came under the writers' observation These pathogens affect many species of shrubs and trees in Colorado, including aspen, cottonwood, lombardy and other poplars, apple, cherry, peach, plum, birch, willow, honeylocust, mountain ash, silver maple, spruce, and Siberian elm. Cytospora canker is one of the most common fungal diseases of Colorado blue spruce. Sept. 1,1931 A Cytospora Canker of Apple Trees 433 in the 1928 growing season or during subsequent years, and eventually all of the dead areas healed over completely. Trees that are 15 years old or older and are at least 20 feet high most typically show symptoms of this disease. This disease can also affect Norway spruce (and less frequently other spruces) as well as Douglas-fir and balsam fir. What is Cytospora canker? Cytospora canker is caused by various species of the fungus Cytospora (sexual genera of Valsa and Leucostoma). In peach production systems, three Cytospora species have been reported as the casual agents of Cytospora canker.