Phomopsis canker of Japanese pear

Symptoms typically appear as sunken, discolored necrotic spots on the bark of trunks and branches. These lesions often expand and merge, girdling the limb.

Exudation of sap or gumming is a common symptom in infected areas as the tree attempts to fight off the fungal invasion. This often leads to severe bark cracking.

Tiny black fruiting bodies, known as pycnidia, become visible on the surface of the dead bark. These indicate that the fungus is actively producing spores for dispersal.

Leaves on infected branches may turn chlorotic, wilt, and drop prematurely. Once a branch is girdled by the canker, it usually dies back completely from the point of infection upwards.

Young shoots may show elongated lesions that eventually cause the shoot to bend or break. These infections often start from pruning wounds or leaf scars.

The causal agent of this disease is the fungus Diaporthe fukushii. It is a serious pathogen primarily affecting Pyrus pyrifolia and other related pear species.

The fungus is a member of the Diaporthaceae family and primarily invades the bark and cambial tissues of the host plant. It can survive in infected twigs and fallen debris for several years.

It reproduces through both asexual (pycnidia) and sexual spores. Pycnidia, appearing as small black dots on the bark, are crucial for the spread of the infection during the growing season.

The pathogen disrupts the vascular system, preventing the tree from effectively moving water and nutrients. This causes the slow decline of the affected branches.

Diaporthe fukushii is highly adaptive, allowing it to remain dormant in tissues during adverse conditions and resume growth when moisture levels rise.

High humidity and moderate temperatures are the most critical factors for the rapid spread of the disease. Prolonged rainy weather favors spore germination.

Mechanical injuries, such as pruning cuts, cracks caused by winter frosts, or sunburn, provide easy access for the fungal spores to enter the host tissues.

Inadequate orchard sanitation, such as leaving pruned branches on the ground, creates a permanent reservoir of spores that reinfect the orchard year after year.

Dense planting configurations that limit airflow and sunlight penetration create humid microclimates, significantly increasing the likelihood of an outbreak.

Trees that are already stressed due to poor nutrition, water deficiency, or pest infestations show higher susceptibility to Diaporthe fukushii infections.

The disease causes significant damage by obstructing the vascular system, which leads to reduced tree vigor, foliage loss, and eventual death of branches.

Economic losses are severe due to yield reduction and the need for frequent replacement of orchards. Infected trees produce fruits of lower quality and quantity.

If not managed correctly, the disease can spread throughout the entire orchard, causing permanent long-term damage to the infrastructure of the plantation.

The pathogen's ability to survive in dead wood makes the disease persistent and difficult to eradicate from affected areas without drastic measures.

Increased costs associated with repeated fungicide applications and intensive labor for pruning and orchard sanitation lower the overall profitability of the crop.

Effective management begins with strict sanitation. All infected branches must be pruned at least 10–20 cm below the visible lesion and immediately removed from the orchard.

All pruning wounds and bark damage should be treated with protective paints or fungicidal pastes to seal off potential entry points for the pathogen.

Chemical control involving copper-based fungicides during the dormant season is highly effective at reducing the primary inoculum levels for the next year.

Maintaining a high level of tree health through balanced fertilization and proper water management helps the trees naturally resist fungal infections.

• Regular disinfection of all pruning tools.
• Timely removal and burning of dead plant material.
• Protective whitewashing of tree trunks.
• Choosing resistant varieties for new plantations.