White leaf spot of elder

The fungus Entyloma serotinum is the causative agent of the white leaf spot disease. It belongs to the order Ustilaginales, commonly known as smut fungi. This pathogen infects the internal tissues of host leaves, forming localized clusters of fungal cells that disrupt normal leaf physiology and cause visible discoloration on the surface.

The disease primarily targets species of the Sambucus genus (elderberry). While it is generally not a lethal disease, it significantly reduces the photosynthetic efficiency of the leaves, which can lead to premature senescence and a decline in the plant's overall health and aesthetic appeal in landscape plantings or wild thickets.

Symptoms are identified by the appearance of pale, white, or light-colored spots on the foliage. These lesions are often circular in shape and can become necrotic over time. By inspecting the undersides of the affected leaves, one can often find a faint, powdery or crust-like fungal growth, representing the spores (conidia) produced by the fungus as it continues its reproductive cycle throughout the growing season.

Environmental conditions play a critical role in the severity of the infection. Entyloma serotinum thrives in humid environments, particularly during seasons with frequent rainfall. High humidity and poor air circulation within the shrub canopy are major catalysts for the rapid germination of spores and subsequent spread of the disease to healthy leaves or nearby plants.

Effective management requires a combination of sanitation and chemical interventions. The primary preventive measure is the removal of fallen leaves during the autumn, as these serve as the overwintering source of the inoculum. Maintaining proper spacing and pruning the shrubs to ensure adequate ventilation can significantly reduce the risk of outbreaks. When necessary, fungicide treatments may be applied to protect vulnerable growth during periods of high infection pressure.

• Sanitary pruning to improve air circulation within the plant canopy.
• Removal and destruction of fallen leaves to eliminate overwintering spores.
• Monitoring for early signs of lesions during periods of wet weather.
• Use of copper-based fungicides if the infection becomes widespread.