The white rot tree fungus, Botryosphaeria dothidea, is often called Botryosphaeria rot or simply "bot rot." The fungus is primarily a problem in apple trees, but it also infects chestnut and crabapple species, among others.
White rot affects the wood and the fruit. Small spots and blisters form on limbs and twigs. The spots expand and create sunken spots called cankers, which ooze watery fluid. Within four to eight weeks, black matter begins to form around the cankers. The cankers form an orange-coloured papery bark as they continue to grow.
Symptoms in Fruit
Sunken brown spots surrounded by red rings form on the outside of the fruit, and eventually the entire fruit rots. Red-skinned apples sometimes lose their colour as they decay, which is how the disease became dubbed "white rot."
The fungus survives in dead plant matter. Remove and prune dead material, including mummified fruit, twigs, spurs and branches, so that the fungus does not spread to healthy trees. Establish a fungicide spray program that extends from the time the plant blooms until harvest to protect wood and fruit against infection.