Exobasidium leaf spot of tea

The causal agent of this disease is the fungus Exobasidium gracile, which belongs to the basidiomycete group. This is a specialized parasite that targets the tissues of the tea plant. The disease type is exobasidiosis, characterized by the formation of distinct galls and deformities on the plant's vegetative organs as the mycelium develops.

The primary crop affected by this pathogen is tea (Camellia sinensis). The infection manifests on young leaves and shoots, which makes it particularly destructive for commercial plantations, as these tender flushes are the core product harvested for high-quality tea production.

The key symptom of the infection involves elongated, often twisted swellings on the leaves, which initially appear pale green or yellowish. As the spores mature, the surface of these affected areas becomes covered in a characteristic whitish-gray bloom composed of fungal basidia and spores, leading to premature tissue hardening and necrosis.

The development of the fungus is favored by high air humidity, frequent fog, and moderate temperatures typical of highland tea-growing regions. Pathogen spores are easily dispersed by rain splash and wind, rapidly infecting healthy bushes in crowded plantings where poor air circulation prevents the leaf surface from drying out quickly.

The harmfulness of Exobasidium gracile lies in significant yield losses and a decline in tea leaf quality. Infected leaves become unsuitable for processing, and chronic infestation weakens the bushes, making them more susceptible to secondary diseases and environmental stress. Control measures include:

• Regular sanitary pruning of affected shoots to reduce the primary inoculum load.
• Maintaining optimal planting density and thinning plantations to improve air circulation.
• Applying copper-based fungicides or specific antifungal treatments during periods of high infection risk.
• Cultivating tea varieties resistant to exobasidiosis as the most effective long-term management strategy.