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Tea grey blight (Pestalotiopsis theae) Photo: placeholder pending image-fill pass

Tea grey blight (Pestalotiopsis theae)

Grey blight of tea, caused by the ascomycete Pestalotiopsis theae (Sawada) Steyaert and related Pestalotiopsis spp., is a chronic foliar disease of tea throughout India, more damaging in the hot, humid plains of Assam, Dooars and Tripura than in the Darjeeling/Nilgiri hills where blister blight dominates. Unlike blister blight, Pestalotiopsis is a secondary, wound- and stress-associated pathogen that exploits hail damage, sun scorch, mite or helopeltis injury and post-pruning shock.

Identification and symptoms

Infection begins at leaf tips or margins as small water-soaked spots that quickly enlarge into circular to irregular lesions with concentric rings. Mature lesions are silvery-grey to dull brown, with a dark thin border, sometimes coalescing across the leaf blade. Tiny black, raised, pinhead acervuli — the asexual fruiting bodies — develop in concentric rings on the upper surface; under a hand lens these are diagnostic. In severe attacks, leaves wither and shed prematurely, exposing maintenance foliage and slowing recovery from pruning.

Hosts and lifecycle

P. theae is restricted mainly to Camellia sinensis and a few related Camellia spp. Conidia released from acervuli are dispersed by rain splash and wind; they germinate at 20-28 °C and require 6-12 hours of leaf wetness. Latent infection is common — the fungus colonises healthy tissue subclinically and erupts after stress. Disease pressure peaks in the post-monsoon (September-November) and again after pruning when fresh wounds and tender foliage are abundant.

Damage and economic impact

Grey blight is rarely catastrophic on its own but routinely causes 5-15% leaf-area loss across affected sections, with measurable impact on flush vigour, recovery after pruning and made-tea quality. It is the principal post-pruning disease in Assam clonal sections.

Management

The Tea Board Plant Protection Code lists grey blight under "wound-pathogen" diseases requiring an integrated approach:

  • Cultural: avoid pruning during cool, wet weather; smooth-cut prune wounds with sharp tools and paint stumps with copper oxychloride paste; balance nitrogen with potash to avoid soft, susceptible foliage; manage shade to reduce extended leaf wetness.
  • Mite and pest control: control Tea Mosquito Bug Helopeltis Tea, thrips and red spider mite to remove entry wounds.
  • Chemical: PPC-approved sprays of copper oxychloride 50 WP 210 g + zinc sulphate 35 g in 40 L water per ha, alternated with carbendazim 50 WP 100 g/ha or hexaconazole 5 EC 200 mL/ha, at 10-14 day intervals during the high-risk window.
  • Resistant material: among TV clones, TV23 and TV26 are rated less susceptible than the older TV1, TV9, TV17 (Tea Tv 1 Tocklai Vegetative Clone).

See also: Tea Blister Blight Exobasidium, Tea Camellia Sinensis Assamica, Tea Camellia Sinensis China Type, Tea Tv 1 Tocklai Vegetative Clone, Tea Mosquito Bug Helopeltis Tea.

References

  1. Tea Research Association Tocklai — Disease Profile. https://www.tocklai.org/
  2. UPASI Tea Research Foundation — Disease Bulletin. https://www.upasitearesearch.org/