Allantoporthe

The first visible sign of the disease is the appearance of characteristic depressed spots of irregular shape on the bark of branches and trunks. Affected areas often darken, taking on a reddish-brown or dark brown hue.

At the site of the lesion, the bark begins to crack, exposing the damaged wood beneath, which often appears loose or decaying. Gumming (gummosis) is frequently observed, indicating deep-seated tissue damage.

Upon close inspection, small black bumps—the pycnidia of the fungus—can be seen on the surface of the dead bark. These are the fruiting bodies from which masses of spores emerge in humid weather as coiling threads or droplets.

As the disease progresses, infected branches gradually wither because the fungus obstructs the transport of water and nutrients. Leaves on such branches turn yellow, curl, and drop prematurely, leaving bare skeletal branches.

In advanced cases, the infection may girdle the trunk, causing the death of the entire tree portion above the lesion site. The disease is chronic, consistently expanding the zone of infection under favorable conditions.

The causal agent of this disease is the ascomycete fungus Allantoporthe leucostoma (synonym Valsa leucostoma). This microorganism acts as a facultative parasite, capable of surviving for long periods as a saprotroph on dead plant tissues.

The fungus actively attacks the bark and cambium of trees, gaining entry through mechanical wounds or frost cracks. Throughout the growing season, the pathogen utilizes conidial and ascosporic stages to facilitate the spread of infection.

The fungal mycelium develops within the bark tissues, gradually destroying cellular structures and triggering necrosis. The biological properties of this pathogen allow it to persist in infected wood even during extreme winter temperatures.

Infection spreads primarily via spores, which are transported by wind, raindrops, or insects. The intensity of an outbreak is directly related to the availability of infection sources in close proximity to healthy plantations.

The development of the fungus is closely linked to the physiological health of the tree, as weakened individuals have a diminished immune response. This makes Allantoporthe particularly dangerous for poorly maintained or damaged orchards.

The development of Allantoporthe is favored by high humidity, particularly during the spring and autumn months. Rainy weather facilitates rapid spore dispersal and germination on vulnerable bark areas.

Sudden temperature fluctuations pose a particular danger, as they cause frost cracks and fissures on the trunks. Such mechanical injuries serve as primary entry points for fungal spores to colonize the plant tissues.

Inadequate orchard maintenance, including a lack of pruning and poor sanitation, creates an ideal environment for pathogen accumulation. Dense planting patterns that inhibit air circulation further exacerbate the risk of disease outbreak.

Reduced plant vigor, resulting from poor mineral nutrition or pest infestations, makes trees significantly more susceptible to the pathogen. Soil waterlogging or prolonged drought can also weaken the protective barrier of the tree bark.

The presence of uncollected plant debris, infected branches, and deadwood in the orchard is the main factor for the disease's annual resurgence. The pathogen is highly resilient and successfully overwinters in various types of plant remnants.

The primary damage from Allantoporthe is the widespread wilting of branches, leading to significant yield loss and reduced fruit quality. Affected trees lose productive canopy area and require intensive corrective pruning.

The disease significantly shortens the lifespan of fruit trees, turning a productive orchard into a source of infection. In severe cases, total tree death can occur within a few seasons.

The disruption of sap flow due to necrotic damage results in small, low-quality fruit on affected branches. Furthermore, the tree’s winter hardiness is severely compromised, leaving it vulnerable to harsh weather conditions.

Economic losses arise from the costs of continuous disease management, yield reduction, and the need to remove irreversibly damaged trees. Widespread infection can lead to the long-term degradation of commercial orchards.

Infected wood becomes brittle and prone to snapping, increasing the risk of branch breakage under the weight of a crop or during strong winds. This creates additional safety concerns for orchard management.

The foundation of control is strict orchard hygiene: the regular removal and destruction of all infected branches. Pruning must be conducted by cutting into healthy tissue, and tools should be disinfected after every cut.

All pruning wounds and mechanical bark damages require prompt treatment with wound dressings or specialized antiseptic paints. This prevents the re-entry of fungal spores into the exposed tissue.

An effective preventive measure is the early spring and autumn whitewashing of trunks and the bases of skeletal branches using lime milk. Whitewashing helps protect the bark from sunscald and subsequent crack formation.

Spraying with copper-based fungicides is recommended during the dormant period, especially after pruning. Systemic fungicides may be used during the growing season if early signs of the infection are detected.

• Ensuring optimal mineral nutrition and irrigation schedules.
• Timely control of bark-damaging insects and pests.
• Selection of cultivars resistant to regional climatic stressors.
• Regular canopy thinning to improve aeration.