Stigmina leaf spot

The disease is caused by the fungus Stigmina hartigiana, an ascomycete pathogen that primarily affects the foliage and shoots of various deciduous trees. This fungus acts as a parasite, infiltrating plant tissues and causing significant physiological stress, which manifests as structural damage to leaves and stems.

The primary hosts of this pathogen include members of the Salicaceae family, particularly willows (Salix spp.) and poplars (Populus spp.), as well as bird cherry trees. It is frequently identified in nurseries, managed landscapes, and wild stands where conditions favor the accumulation of fungal inoculum over multiple growing seasons.

Symptoms are characterized by the development of leaf spots that initially appear as small, chlorotic flecks, eventually darkening to brown or dark gray necrotic lesions. In many cases, these spots are surrounded by a distinct halo. Severe infestations lead to premature defoliation, while infection of the twigs can result in cracking and stunted growth of the branches.

The proliferation of Stigmina hartigiana is strongly correlated with high humidity levels and prolonged wet weather during the spring and early summer months. Spores are disseminated by rain splash, wind currents, and potentially by insects. The fungus overwinters in infected twigs, bark fissures, and leaf litter, providing a persistent source of infection for the subsequent season.

The economic and ecological impact includes reduced photosynthetic efficiency, which leads to stunted tree growth and diminished vigor. To effectively manage this disease, integrated pest management strategies are recommended:

• Removal and destruction of fallen leaves to reduce inoculum.
• Pruning and removal of infected branches during dormant periods.
• Application of copper-based fungicides or appropriate systemic chemicals during the early spring to protect new growth.