Powdery mildew of Ericaceae

Podosphaera myrtillina is a fungal pathogen belonging to the order Erysiphales, known primarily as the causative agent of powdery mildew on various species within the Ericaceae family, particularly the genus Vaccinium. As an obligate biotroph, it thrives by colonizing the surface of leaves, flowers, and young stems, drawing nutrients via specialized structures called haustoria.

The disease manifests as a distinctive white, powdery fungal growth that spreads rapidly across the plant tissues. While often considered a secondary concern compared to other fungal issues, heavy infestations of Podosphaera myrtillina can lead to severe physiological stress in blueberry and cranberry crops, resulting in stunted growth and significant fruit yield reduction.

The biological cycle of this fungus involves both asexual and sexual reproduction phases. The asexual stage produces abundant conidia, which are dispersed by wind throughout the growing season to infect new tissues. In the fall, the fungus produces overwintering structures known as chasmothecia (formerly cleistothecia) on dead leaves and plant debris, ensuring its survival during colder months.

Environmental conditions play a critical role in disease dynamics. The pathogen flourishes in warm, humid weather, though it does not strictly require leaf wetness for infection. High planting densities and lack of adequate ventilation create a microclimate conducive to rapid outbreaks, often requiring proactive management of the orchard’s environment to break the infection cycle.

Economic damage is caused by the necrosis of foliage, premature leaf drop, and weakened plant vigor, which directly impacts the return on investment in berry production. Effective management involves a combination of strategies: maintaining good orchard hygiene, promoting air circulation through proper pruning, and applying targeted fungicide treatments during high-risk stages of the plant's development to prevent the spread of conidia.