Blister blight of tea

Blister blight, caused by the obligate parasite Exobasidium vexans, is considered one of the most destructive diseases affecting the tea industry globally. This fungus specifically targets the young, succulent parts of the plant, potentially causing severe yield losses if not managed appropriately within commercial tea estates.

The host range is primarily limited to tea plants (Camellia sinensis). The pathogen attacks the young leaves, stems, and buds, often referred to as flushes, which are the main components harvested for tea production. By damaging these tissues, the fungus directly interferes with the economic output of the plantation.

The symptoms of the disease are characterized by the development of small, translucent spots on young leaves. As the infection progresses, these spots expand into circular, blister-like structures that turn pinkish or reddish. On the underside of these lesions, a white, velvety coating of fungal spores develops. Infected shoots often become distorted, thickened, and brittle, leading to the necrosis of tender tissues.

Environmental conditions play a critical role in the disease cycle. Exobasidium vexans thrives in cool, humid climates with frequent cloud cover or high precipitation. The fungus requires high humidity for spore germination and infection. Dense planting patterns and poor airflow within the canopy significantly exacerbate the spread of the disease during monsoon or rainy seasons.

Integrated pest management (IPM) is essential for controlling blister blight. Effective strategies include:

• Pruning to ensure proper canopy management and improved aeration.
• Selecting resistant or tolerant tea clones for planting.
• Judicious use of nitrogen fertilizers to avoid excessive succulent growth.
• Implementing a strict schedule of fungicide applications during high-risk periods.
• Regular field monitoring to detect and eliminate early infection spots before they spread.