Aureobasidium prunicola

The causal agent of this plant disease is the fungus Aureobasidium prunicola. It is a filamentous fungus that primarily acts as a pathogen causing leaf spot symptoms. Its biological nature allows it to survive in various environments, often remaining latent within plant tissues or on the surface of infected organs until conditions become favorable for colonization and disease development.

The primary hosts for this pathogen are stone fruit trees belonging to the Prunus genus. Plum trees (Prunus domestica) are most frequently reported to suffer from this infection. However, the fungus can also impact other related species like cherries and damsons, especially in regions with high humidity levels and limited air circulation within the orchard canopy.

Diagnostic symptoms include the formation of irregular necrotic spots on the leaves. As the infection progresses, these spots may coalesce, causing significant tissue death. In humid conditions, a characteristic dark, velvety growth can be observed on the underside of the leaves, which corresponds to the conidial mass of the fungus. This stage is crucial for the pathogen's secondary spread throughout the orchard.

The development and spread of Aureobasidium prunicola are heavily dependent on environmental variables. High humidity, prolonged leaf wetness, and moderate temperatures are the primary drivers of disease outbreaks. The fungus overwinters in fallen leaf litter and on the bark of infected branches, creating a reservoir for new infections every spring when temperature and moisture conditions align.

Effective control measures require a combination of cultural and chemical strategies. Sanitation is paramount, involving the removal and destruction of fallen leaves to reduce the primary inoculum. Maintaining proper orchard hygiene, including systematic pruning to ensure adequate sunlight penetration and airflow, significantly inhibits fungal growth. If necessary, targeted fungicide applications during the early stages of leaf development can provide substantial protection against the disease.