Powdery mildew of blueberry

The causal agent of this disease is the obligate parasite Erysiphe vaccinii, a fungus belonging to the Erysiphales order. This pathogen is specialized in infecting plants of the Ericaceae family, commonly impacting blueberries (Vaccinium species), cranberries, and other related shrubs in both wild environments and commercial cultivation.

The primary hosts affected by this fungus include blueberry and cranberry bushes. The infection primarily targets young foliage and tender green shoots, though it can also colonize the surfaces of leaves throughout the growing season. If left untreated, the fungus can survive in dormant buds and fallen debris, posing a risk for subsequent years.

The most diagnostic sign of the infection is the appearance of white, dusty mycelium patches on the upper surface of the leaves. As the disease progresses, the white patches may expand to cover the entire leaf surface. Infected leaves often become distorted, curled, and may develop reddish or purplish discoloration before turning necrotic and dropping prematurely.

Disease development is favored by warm, humid conditions, especially when there is high relative humidity combined with low rainfall. While moisture on the leaf surface is not required for the germination of the fungus, humid air is essential. Poor air circulation within dense canopy structures significantly accelerates the spread of conidia across the field.

The economic impact of Erysiphe vaccinii is linked to reduced photosynthetic capacity, which weakens the plant and decreases fruit production. Management strategies focus on sanitation and chemical intervention, such as:

• Pruning and destroying infected branches to reduce inoculum.
• Improving air circulation through proper plant spacing.
• Applying preventive sulfur-based fungicides during the early season.
• Using systemic fungicides if a severe outbreak is detected.