Exobasidium maculosum

Exobasidium maculosum is a fungal pathogen classified within the division Basidiomycota and the class Exobasidiomycetes. This fungus is specifically known for causing localized leaf spot symptoms on highbush blueberry (Vaccinium corymbosum) plants. As a parasitic organism, it exclusively targets the green tissues of the host, leading to visible pathological changes.

The disease manifests as distinct spots on the upper surface of blueberry leaves, which initially appear light green or yellow and often progress to vibrant red or brownish hues. On the underside of these spots, a white, felt-like layer of mycelium and fungal spores develops, which is a diagnostic feature used to identify this specific pathogen in the field.

The life cycle of the pathogen is highly dependent on environmental moisture. Spore germination and subsequent infection of new leaf tissues occur primarily during spring, coinciding with periods of high humidity and moderate temperatures. The spores are typically disseminated by splashing rain and air currents, allowing the fungus to spread rapidly within a dense plantation.

The economic impact of Exobasidium maculosum is significant due to the reduction of effective leaf area, which impairs photosynthesis. This leads to premature defoliation, which severely stresses the plant, reduces berry size and yield, and compromises the plant's ability to store sufficient carbohydrates for winter survival and next year's growth.

Effective management strategies require a combination of cultural practices and chemical control. Growers should focus on improving air circulation within the canopy through selective pruning and removing infected plant debris. If infections are severe, the application of appropriate fungicides, particularly those recommended for Basidiomycete control, should be performed early in the season to prevent secondary spread.