General Information. In eastern Washington, perennial canker and bull's eye rot of apple, caused by Cryptosporiopsis perenanns, are chronic diseases of apple wood and fruit, respectively. First reported in the Pacific Northwest in 1925, perennial canker has since been documented in several areas of North America, England, and continental Europe. Perennial canker does not typically result in tree loss, but the conidia produced on canker surfaces are potential inoculum for infection of fruit and subsequent development of bull's eye rot. The latter is one of the most serious postharvest diseases of apple in Washington state. Fruit inoculation reportedly occurs during rainy periods near harvest , whereas the infection process and symptom development occur while the fruit is in controlled atmosphere storage. Severe outbreaks of bull's eye rot occurred in Washington in 1985, 1987, and 1988.  The disease is etiologically similar to apple anthracnose, which is caused by a closely related fungus.

Symptoms.The most characteristic symptom of perennial canker is the occurrence of concentric rings of dead wood around a sunken center. The canker is not truly perennial since the fungus causing the disease does not progress from one year to the next in the wood.   Rather, new infections occur each year so that the cankers result from repeated annual infections. The disease usually starts around a pruning wound or some other injury on a stem. Healthy callus tissue develops and is invaded by the woolly apple aphid. In feeding, these insects create small wounds and injure the surrounding tissue. The fungus then invades and develops in this injured tissue. Winter injury of the tissue is an important factor in the advance of the canker. Cankers progress farther following severe winters than after mild ones. In the spring, healthy callus again is formed at the margin of the canker and the cycle is repeated resulting in another ring of dead tissue. In addition to the presence of woolly aphids and low winter temperatures, any factor that produces excess succulent growth, such as high nitrogen fertilization or overirrigation, or that weakens the tree, increases the severity of perennial canker.

Bull's eye rot is a postharvest disease that is usually observed when infected fruit are removed from storage. 

The disease gets its name from the lesions that frequently are comprised of concentric rings of necrotic tissue.  Cream colored tufts of spores are sometimes present.  Infection occurs in the orchard around petal fall or just before harvest.

Epidemiology.  The perennial canker fungus is a wound parasite, entering the tree through pruning wounds, frost cracks, or wooly aphid injuries. In Washington, pruning wounds and wounds from frost cracks are frequent infection courts. The fungus survives the winter as mycelium and conidia in cankers and as conidia on rotten fruit left on the orchard floor. Sporulation occurs throughout the year, peaking during fall and winter. Conidia are exuded from aceruli (fungal fruiting bodies on the canker surface) in a gelatinous substance and dispersed by the impaction of water droplets. Host susceptibility is highest between October and February. The annual reactivation of cankers is due to conidial infection of the callus ring surrounding the canker. The wooly aphid is attracted to the succelent callus tisue around the canker margins and feeds on it. The galls produced as a result are more sensitive to low temperatures than normal bark tissue. Gall tissue ruptures at -17.8 C or lower. Conidia are dispersed to these wound sites, where new infections are established.

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Management.  There is considerable difference in susceptibility of varieties to perennial canker. Golden Delicious, Gala, Jonagold, Criterion, Granny Smith, Newtown, Rome Beauty, Jonathan, and Spitzenberg are among the most susceptible while Red Delicious, McIntosh, Winesap, Wealthy, and Gravenstein are more resistant. Several things may be done to reduce losses from perennial canker. In areas where the disease is serious, the more resistant varieties should be planted. Trees should be kept in a good state of vigor, and extremes of either too much or too little fertilization, irrigation, and pruning should be avoided. Because of the important part woolly aphids play in the development of the disease, these insects should be controlled, if not eliminated. A program of protective sprays applied during fruit development and just before harvest will help prevent bull's eye rot. Fruit should be kept as dry as possible after harvest. Picked fruit should not be left in the orchard during rainy weather.

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