Disfigurations of apple tree bark may indicate benign growths or healthy scar tissue over old wounds. Patches of dead bark could be symptoms of disease or indicators of poor growing conditions. When bark dies, the underlying wood usually dies as well. Pruning and treatment may save the life of the tree, but prevention of these serious problems is the best approach.
Growths and Injuries
On small trees, exposed sections of the trunk could sunscald with splitting dead bark on the sunny side of the tree. Hailstones sometimes split bark on impact and mower injuries to the base of trees are common. Painting or sealing injuries could interfere with the healing process. Fungicide protects against infection of exposed wood while the bark grows over the wound.
Nectria fungus invades open wounds in apple tree bark. This fungus grows into the heartwood and sapwood of the tree where fungicide treatments won't affect it. Nectria kills the new bark that would cover the wound. Nectria cankers expand year by year and eventually girdle and kill the tree. Don't accept nursery stock with signs of nectria infection. Prevent injury to established trees by keeping mowing machinery away from the trunks.
Choose resistant cultivars for the best protection against fire blight, a serious bacterial infection. Fire blight infects blossoms and spreads quickly to other parts of the apple tree. Insects could spread the illness from tree to tree--contaminated pruning tools also put the orchard at risk. Antibiotic sprays prevent blooms from becoming infected. Diseased limbs should be cut away in the dormant season. Disinfect tools in a chlorox solution before trimming healthy trees.
White rot and black rot cause similar damage, girdling and killing branches or even entire trees. Infection can invade open wounds, the cankers caused by other diseases, or grow on leaves during wet weather. Regular spraying of fungicides throughout the growing season prevents rot infections as well as many other fungal problems. Cankers and dead limbs should be cut out when the tree goes dormant. Burn the prunings away from the orchard and scatter the ashes to expose and kill remaining spores. Old fruit left beneath trees harbors the rot fungus as well as many insect pests.
Phytophthora fungus should only be a problem in poorly drained areas. Apples growing in wet ground easily succumb to root rot. Treatment with fungicide does not solve this problem. Choose well drained ground for apple trees and slightly mound soil around the base of the tree to drain water away from the trunk.
Many types of mushrooms infect wounds on living trees. Lightning strikes, wind damage and broken limbs from heavy loads of fruit expose apple trees to fungal problems. Pruning out storm damaged wood minimizes exposure. Most major pruning should only be done in winter when the chance of infection is slight. Fungicide can help prevent trouble, but deep infections are untreatable.