Fusicoccum canker

The fungus is characterized by its ability to act as an endophyte, existing within the host tissues for a long time without causing visible symptoms until the tree experiences environmental stress, such as drought or frost.

It reproduces via pycnidia, which are small, dark fruiting bodies that break through the plant's epidermis to release conidia. These spores are primary agents for spreading the disease within and between trees.

The pathogen thrives in warm, humid conditions. It is opportunistic, meaning it rapidly colonizes weakened host plants, taking advantage of the reduced defensive capabilities of the tree's vascular system.

The distribution of the fungus is widespread globally, affecting both urban landscapes and natural forest ecosystems where environmental conditions favor the development of the pathogen.

The primary host for Fusicoccum aesculi is the horse chestnut (Aesculus hippocastanum), but the pathogen is known for its wide host range, infecting various deciduous trees including apple, birch, and diverse ornamental shrubs.

The damage manifests as cankers on the bark, which can eventually girdle the stems or branches. Once the stem is girdled, all plant parts distal to the infection point will wilt and die due to the disruption of sap flow.

Infected trees suffer from significant dieback, leading to a loss of foliage and structural integrity. Chronic infections result in the gradual decline of the tree's health and eventual mortality.

Beyond the direct impact on the host, the damage makes the tree highly susceptible to secondary infestation by bark beetles and wood-boring insects, which accelerate the destruction of the tree.

The overall impact on the environment includes the loss of shade trees in urban settings and a substantial reduction in the aesthetic and ecological value of public parks and gardens.

The initial signs of infection include the appearance of reddish-brown or sunken bark patches. These areas often appear near wounds, pruning cuts, or natural bark cracks.

As the infection progresses, the bark in these areas may crack or flake off. If the bark is removed, the underlying cambium layer often appears necrotic, exhibiting a brown and discolored appearance.

Wilt symptoms occur as the pathogen disrupts the water-conducting tissues. Leaves on infected branches may yellow or turn brown prematurely and often remain attached to the tree long after they have died.

Tiny black pycnidia (fruiting bodies) become visible on the surface of the dead bark. During humid weather, these can release a gelatinous mass of spores, which may appear as shiny droplets on the surface.

Branch dieback is a key diagnostic feature, especially when it occurs in a pattern that follows the location of a canker. The presence of these cankers on the main trunk is particularly critical for the long-term survival of the tree.

Management of Fusicoccum canker relies heavily on sanitation. Pruning out infected branches is essential, ensuring that cuts are made well below the canker into healthy wood to remove all traces of the pathogen.

Tools used for pruning must be disinfected with alcohol or other appropriate sanitizers between cuts to prevent spreading spores from infected to healthy branches.

Providing optimal growing conditions is a proactive measure. Adequate irrigation during dry spells and proper fertilization help maintain tree vigor, reducing the risk of opportunistic fungal colonization.

Protective fungicide applications, particularly those containing copper, can be used to treat wounds or provide a barrier on healthy bark, although they are primarily preventative rather than curative.

• Remove and destroy all infected plant material.
• Disinfect all pruning equipment consistently.
• Avoid wounding tree bark during maintenance work.
• Monitor trees for early signs of bark discoloration.