Lophodermium needle cast of rowan

Lophodermium leaf spot, caused by the fungus Lophodermium aucupariae, is a significant pathology affecting various species of the Sorbus genus. This fungal pathogen primarily targets the foliage, leading to premature leaf drop and the overall weakening of the tree host.

The disease mainly impacts rowan trees (mountain ash) in both wild and cultivated settings. It is frequently observed in nurseries and landscapes where poor air circulation and high humidity levels prevail, creating an ideal environment for fungal spores to settle and infect healthy tissues.

Symptoms of the infection typically appear as irregular spots on the leaf blades. As the disease progresses, these spots expand, and small, elongated, black structures called apothecia develop on the underside of the leaves. These structures serve as the site for spore production, which allows the fungus to spread further during the growing season.

Environmental conditions play a crucial role in the development and spread of Lophodermium aucupariae. Cool, wet weather during spring and summer facilitates the germination of spores. The fungus survives the winter primarily in infected fallen leaves, which act as a reservoir for recurring infections in the following year.

The impact of this disease on tree health is primarily physiological. By causing premature leaf senescence, the fungus limits the tree's ability to photosynthesize and store energy, making it more susceptible to environmental stress. Effective management includes:

• Meticulous removal and destruction of fallen leaves in autumn.
• Pruning branches to improve crown ventilation and sunlight exposure.
• Application of appropriate fungicides during the early stages of infection.