high severity

Tea Blister BlightIdentification & Treatment Guide 2026

Exobasidium vexans · Family: Exobasidiaceae

Tea blister blight (Exobasidium vexans) causes translucent blister-like swellings on young tea leaves that turn brown and papery. It attacks only the young flush that is harvested for tea. Manage with regular plucking (7-day rounds), copper fungicide sprays, good drainage, pruning for air flow, and hexaconazole application during wet weather.

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Quick Diagnosis

high

Tea Blister Blight

Affects: young leavesbudsyoung stems
Peak Season: Cool wet weather (15-25°C), misty conditions, monsoon season in South Asia
Spread Risk: Fast
Spread By: Wind-dispersed basidiospores, rain splash

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Symptoms: What does Tea Blister Blight look like?

Visual identification guide — tap each stage for details

Small translucent spots on young tea leaf from blister blight — Initial translucent spots on young expanding tea leaf

Raised convex blisters with white underside on tea leaf — Characteristic raised blister with white sporulation underneath

Severe blister blight with brown papery lesions on tea shoots — Dried brown blisters and shoot distortion — unmarketable flush

Early Stage

Small translucent spots on young leaves
Small (2-5 mm) translucent, light-colored spots appear on the upper surface of young expanding leaves. Spots are initially pinhead-sized and easy to miss.

Mid Stage

Convex blisters with white sporulation underneath
Spots enlarge into raised, convex blister-like swellings (5-15 mm) on the upper surface. The underside of the blister shows white, velvety basidiospore production. Blisters have a translucent, watery appearance.

Late Stage

Brown papery blisters and shoot dieback
Blisters dry to brown, papery, sunken spots. Heavily infected shoots become distorted, twisted, and may die back. Severely blistered leaves are rejected during plucking, reducing made tea output.

Causes: Why is my plant getting Tea Blister Blight?

Environmental triggers and disease cycle

Cool temperatures (15-25°C) with persistent mist and overcast weather
High rainfall and humidity above 80%
Stagnant air in sheltered valleys
Dense shade and poor air circulation within the bush canopy
Continuous presence of young succulent flush (the only tissue susceptible)

Disease Lifecycle

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Host Plant

Susceptible crop

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Pathogen

Exobasidium

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Conditions

Cool wet weather (15-25°C), misty conditions, monsoon season in South Asia

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Infection

Penetrates tissue

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Symptoms

Visible signs

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Spread

Wind-dispersed basidiospores

How to Treat Tea Blister Blight

Tick each step as you complete it — works offline too

🌿 OrganicSafe for all farms

Organic Treatment Steps

4 steps

Maintain regular plucking rounds (every 7 days) — removing susceptible young flush reduces available tissue for infection.
Apply copper oxychloride at 3 g/L during high-risk weather periods (misty, cool, wet).
Prune bushes to maintain an open, well-ventilated canopy that dries quickly after rain.
Manage shade trees to allow some sun penetration — avoid excessive shade.

🧪 ChemicalUse protective equipment

Chemical Treatment Steps

4 steps

Apply hexaconazole (Contaf 5EC) at 1 ml/L every 7-10 days during the peak blister blight season.
Propiconazole (Tilt 250EC) at 0.5 ml/L as alternative systemic fungicide.
Apply copper hydroxide (Kocide 2000) at 2 g/L as protectant during moderate disease pressure.
Note: Observe pre-harvest interval (PHI) of 7-14 days between last spray and plucking to ensure residue compliance.

Prevention & Seasonal Calendar

Year-round protection plan for your crops

Pre-Planting

Maintain regular plucking (7-day rounds) to remove susceptible flush
Prune bushes and shade trees for good air circulation

Mid-Season

Apply preventive fungicides at the onset of cool wet weather
Ensure adequate drainage — avoid waterlogged conditions around bushes

Post-Harvest

Select planting sites with good air drainage — avoid sheltered hollows

🛡️ Resistant Varieties

TRI 2025 (Sri Lanka, tolerant)TRFK 6/8 (Kenya, tolerant)Some Assam clones show moderate tolerance

View full seasonal calendar for your region →

Frequently Asked Questions

Common questions about Tea Blister Blight

Why does blister blight only affect young leaves?

E. vexans can only infect actively expanding, succulent young tissue (the 'flush'). As leaves mature and harden, they become resistant. This is why only the youngest 2-3 leaves and bud are affected — which unfortunately are exactly the leaves plucked for tea manufacture. Mature leaves on the bush are immune.

Does blister blight affect tea quality?

Yes. Blistered leaves produce made tea with dull liquor, reduced flavor, and off-notes. Tea buyers reject lots with high blister blight damage. For premium teas (Darjeeling first flush, Sri Lankan highland), even moderate blistering can cause significant price reductions.

Why is blister blight seasonal?

The fungus requires very specific conditions: cool temperatures (15-25°C), persistent mist or light rain, and high humidity. These conditions occur seasonally in highland tea regions — during the monsoon in India/Sri Lanka, or during the long rains in Kenya. During dry or warm periods, blister blight naturally declines because basidiospores desiccate rapidly and cannot infect without free moisture.

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Affected Plant

Tea

Camellia sinensis

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Treatment Guide

Full Treatment Protocol

Detailed spray schedule & dosage guide

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