Granulobasidium vellereum

The primary symptom of this disease is the appearance of a felt-like fungal growth on the branches and trunks of the tree. This texture is the hallmark characteristic of the pathogen's presence.

Infected branches undergo a gradual dieback process. Gardeners often mistake these symptoms for winter injury, as the bark may crack and reveal discolored wood underneath as the fungus colonizes the tissue.

As the infection progresses, the fungus produces flat, crust-like fruiting bodies that adhere tightly to the bark. These can range from cream to grayish or light brown in color.

The disease impairs the tree's vascular system, leading to premature yellowing and leaf drop on affected branches. Over time, the conductive tissues become completely blocked, causing the limb to wither.

Early-stage diagnosis is difficult because the mycelium develops hidden beneath the bark. Often, the damage is only fully visible once the fungus begins to produce its reproductive structures on the surface.

The causal agent is the fungus Granulobasidium vellereum, a member of the Basidiomycota phylum. It functions as a wood-decaying pathogen that can act as a weak parasite on stressed trees.

The pathogen enters the plant primarily through mechanical wounds, pruning cuts, frost cracks, or sunscald. Once inside, the fungus spreads through the woody tissue, slowly consuming its components.

Biologically, this fungus exploits trees with compromised natural defenses. While healthy trees may resist, once the mycelium gains a foothold, it spreads effectively within the woody structure.

The fungus overwinters as mycelium within the infected branches. When favorable conditions return in the spring, it resumes growth and begins spreading spores to nearby susceptible hosts.

As a wood-rotting species, it breaks down cellular walls, leading to the loss of structural integrity of the affected woody parts, which can have long-term consequences for tree longevity.

High humidity and moderate temperatures are the most critical factors for the development of Granulobasidium vellereum. Prolonged rainfall significantly increases the risk of spore germination.

Trees suffering from physiological stress—caused by drought, waterlogging, or poor soil nutrition—are significantly more susceptible. Their weakened state allows the fungus to overcome natural defenses.

Poor orchard management, such as dense canopy growth and inadequate air circulation, creates an ideal microclimate for fungal proliferation. Trapped moisture on bark surfaces aids infection.

Old, rotting wood, stumps, and neglected pruning debris within or near the orchard serve as major sources of inoculum, allowing spores to travel to healthy trees via wind and water.

Temperatures ranging between 15°C and 25°C are considered optimal for the vegetative growth of the mycelium and the subsequent production of fruiting bodies on the tree's surface.

The main threat is the progressive death of branches, which leads to reduced yields and overall canopy decline. If left untreated, the entire tree may lose structural integrity.

Infections on the main trunk are particularly dangerous as they can lead to the total collapse of the plant by cutting off the supply of water and nutrients to the entire crown.

The wood affected by this fungus loses its mechanical strength, becoming brittle and prone to breaking during heavy fruiting or strong winds, which creates a safety risk in orchards.

Economic damage includes the costs of intensive pruning, potential tree removal, and loss of productivity. Fruit quality is often reduced due to the disruption of transport systems within the plant.

The disease is chronic, meaning that without intervention, an orchard can experience a rapid increase in infected trees, turning the site into a chronic source of disease for surrounding areas.

The primary control measure is the immediate sanitary pruning of all infected limbs, ensuring that cuts are made into healthy, clean wood. Tools must be disinfected after every single cut.

All pruning wounds larger than 2 cm in diameter should be sealed with horticultural wax or a protective fungicidal paste to prevent spores from entering the fresh wood tissue.

Preventive maintenance, such as trunk whitewashing and cleaning the bark of mosses, helps keep the tree's protective layer healthy and makes it easier to spot early signs of infection.

Maintaining high horticultural standards, including balanced fertilization and proper irrigation, enhances the tree's inherent immunity and helps it withstand fungal threats.

• Apply copper-based fungicides in early spring to inhibit spore germination.
• Remove and destroy all stumps and dead wood that could harbor fungal spores.
• Prune regularly to improve light penetration and airflow, reducing humidity in the canopy.