Blueberry red leaf spot

The causal agent of the disease known as blueberry red leaf spot is the basidiomycete fungus Exobasidium vaccinii. This phytopathogen is a member of the Exobasidiaceae family and primarily targets members of the Ericaceae family, with Vaccinium species being particularly susceptible to its parasitic activity.

The primary visual symptoms include the appearance of distinct red, crimson, or purple spots on the upper leaf surfaces during the spring and early summer. As the fungus progresses, a white to pinkish powdery layer develops on the underside of these spots, which represents the fungus's sporulation (basidia and basidiospores). Severely infected leaves may thicken, curl, and suffer from premature abscission.

The life cycle of Exobasidium vaccinii is synchronized with the vegetative growth of its host. The fungus spreads via wind-borne or rain-splashed basidiospores that land on new foliage. The infection persists within the plant tissue, where the fungus overwinters as mycelium, ensuring its survival from one season to the next within the stems and shoots of the blueberry bush.

Development and spread are favored by prolonged wet weather, high humidity, and moderate temperatures during the flushing stage. Poor orchard sanitation and dense canopy foliage, which traps humidity and prevents rapid drying of leaves after rain, create the perfect microclimate for the disease to flare up and infect large sections of a plantation.

Economic damage is caused by the reduction of the plant's photosynthetic capacity, which leads to stunted growth, reduced berry yield, and decreased overall vigor of the plantation. Effective control strategies prioritize cultural practices such as pruning out infected branches to remove the inoculum source, ensuring optimal spacing for air circulation, and the judicious application of protective fungicides during the early leaf-development stage.