Ash fruit necrosis

Neosetophoma samarorum is a fungal pathogen responsible for causing disease in the samaras (winged fruits) of ash trees. This specific fungus belongs to the order Pleosporales and is recognized as an agent of seed necrosis, which can significantly affect the reproductive capacity of ash populations in both natural forests and urban landscapes.

The primary host for this pathogen is the European ash (Fraxinus excelsior). The fungus primarily targets the generative organs of the tree. Infections typically begin when the samaras are developing, but the disease can continue to progress during storage if the seeds are not properly dried and stored in ventilated conditions.

Symptomatology of the infection involves the appearance of dark, brown to black necrotic lesions on the surface of the fruit wings. As the disease progresses, the internal tissues of the samara degrade, and in humid environments, the fungus may produce small, dark pycnidia, which are the fruiting bodies responsible for releasing spores into the surrounding area.

Development and spread of Neosetophoma samarorum are highly dependent on weather conditions, particularly high humidity and moderate temperatures. The fungus spreads through rain splash and wind dispersal of conidia. Areas with poor airflow within tree canopies or crowded nursery conditions provide ideal environments for the rapid spread of the disease.

The economic and ecological impact of this disease is primarily linked to the reduction in seed viability and germination rates. To manage and prevent the spread of the pathogen, professional foresters and arborists should implement the following strategies:

• Strict sorting of harvested seeds to remove symptomatic material.
• Proper drying of seeds to prevent moisture accumulation during storage.
• Application of prophylactic fungicides in seed orchards during high-risk periods.
• Regular monitoring of tree health in nursery environments.