Diaporthe canker of fruit trees

The disease is caused by the fungus Diaporthe ambigua, an ascomycete pathogen responsible for canker formations and bark necrosis on woody plants. The pathogen creates long-term stress for the host tree, often leading to limb dieback and localized cell death within the cambium layer.

The primary hosts for Diaporthe ambigua include pome fruits such as pears and apples. However, the pathogen is also capable of infecting stone fruits and various ornamental tree species, particularly targeting trees that are already compromised by environmental stress or improper pruning.

Symptoms typically present as sunken areas on the bark, which darken and expand over time. As the infection progresses, the bark develops deep fissures, exposing the wood underneath. Small, black, pimple-like structures known as pycnidia appear on the surface of the cankers, serving as the primary source of inoculum for further spread.

The development of this disease is heavily influenced by humidity and rainfall, which facilitate the dispersal of spores from pycnidia. Wounds caused by mechanical damage, frost, or sunburn provide critical entry points for the fungus to colonize the tree's vascular system, leading to systemic weakness and eventual failure of affected branches.

Management of Diaporthe ambigua requires a proactive approach centered on sanitation and environmental control:

• Regular pruning of infected branches, ensuring tools are disinfected between cuts.
• Application of copper-based fungicides during the dormant season to reduce fungal load.
• Improving overall tree health through balanced fertilization and irrigation.
• Protecting tree trunks from extreme sun exposure and winter damage to minimize entry sites for the pathogen.