Perennial canker

Perennial canker is a serious plant disease caused by the fungus Neofabraea perennans (formerly known as Gloeosporium perennans). It primarily affects the bark of trunks and scaffold branches, while also causing a characteristic storage rot known as bullseye rot in harvested fruits.

The disease frequently attacks Malus domestica (apple tree) and Pyrus communis (pear tree). It is characterized by its chronic nature, as the fungus remains active in the necrotic tissues year after year, gradually expanding its impact on the wood and causing significant structural damage.

Symptoms include sunken, discolored patches on the bark that develop into open cankers. As the tree attempts to heal, a callous layer forms around the wound, which the fungus subsequently reinfects, creating a classic concentric "target" appearance. On fruits, the disease appears as circular, brown, slightly depressed lesions that rot quickly during storage.

The development and spread of the disease are favored by cool, moist conditions. Spores are primarily disseminated by wind, rain splashes, and insects, entering the tree through pruning wounds, frost cracks, or sites of previous mechanical damage. High humidity during the ripening phase increases the risk of fruit infection.

The economic impact of perennial canker is severe, leading to limb dieback, reduced orchard longevity, and substantial fruit losses during cold storage. Effective management strategies include:

• Performing thorough sanitation by pruning and removing infected wood.
• Applying protective wound dressings to all pruning cuts and bark injuries.
• Implementing a seasonal fungicide spraying program to inhibit spore germination.
• Promoting overall tree vigor to minimize susceptibility to frost damage and canker colonization.