Blueberry powdery mildew

Microsphaera vaccinii is a fungal plant pathogen within the order Erysiphales, commonly associated with the development of powdery mildew on various species of the Ericaceae family, including highbush blueberry and cranberry. Although taxonomic revisions sometimes classify this fungus under the genus Erysiphe, it remains a recognized pathogen that significantly affects berry production systems globally.

The primary symptom of infection is the emergence of white, flour-like mycelial growth on the surface of leaves, shoots, and sometimes fruits. As the infection progresses, the leaves may curl, become stunted, or develop necrotic spots. This covering of fungal growth interferes with the plant's ability to undergo photosynthesis, thereby reducing vigor and yield potential throughout the growing season.

The disease cycle of this pathogen relies on both asexual and sexual reproduction phases. During the growing season, wind-dispersed conidia spread the infection rapidly from plant to plant. As the season ends, the fungus produces overwintering structures known as chasmothecia (formerly cleistothecia). These structures survive the winter on infected plant debris, ensuring the cycle repeats once spring temperatures begin to rise.

Environmental factors are critical for the successful establishment of Microsphaera vaccinii. The fungus thrives in humid conditions and moderate temperatures, typically between 18°C and 25°C. In commercial berry orchards, high plant density and poor canopy management create microclimates with increased humidity, which facilitate the rapid spread of spores and escalate the severity of the outbreak.

Effective management and control strategies are essential for protecting yield quality and plant longevity. Integrated pest management (IPM) is the most efficient approach, focusing on site selection, pruning to enhance airflow, and the removal of infected foliage. Chemical controls, including sulfur-based products or systemic triazole fungicides, are recommended when weather conditions favor disease development and early symptoms are detected in the field.