Tea

Plant protection

Root diseases

Black root disease (Rosellinia arcuata)

Black, wooly mycelium on root surface and at collar White and star shaped mycelium on wood surface   Girdling and canker at collar region                             Black lead-shot like perithecia seen occasionally, on collar                                            Mycelium grows freely through surface soil and organic matter Spreads rapidly in damp weather

Control measures

• Remove surface mulch around 10 m

• Drench soil with Dithane M 45 or Captan - 30 g / 10 litres of water

• Avoid soil rehabilitation

Red root disease (Poria hypolateritia)

	Fast spreading and slow killing Mycelium white, later turns red, in advanced stages may appear black Interwoven with adhering soil On washing soil goes off - blood red mycelium seen
Wood spongy and sodden Fructification plate like with spores at collar -rarely seen Spreads mostly by root contact Alternate hosts : Coffee, grevillea, albizia, and erythrina

Brown root disease (Fomes noxius)

Common in low elevation Slow spreading and quick killing Soil encrustation, which cannot easily be washed off Mycelium tawny brown resembling sambur skin
Wood turns soft and spongy Honey- comb like reticulations on the wood Fructification seen on stumps- bracket shaped, irregular and hard Spores carried by wind, lodges on stumps of shade trees Infection spreads mainly through root contact Alternate host : Coffee, Grevillea, Albizia, and Erythrina

Control measures:

Phytosanitary measures and drenching the soil with tridemorph or hexaconazole 0.5% are recommended.

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Charcoal stump rot (Ustulina zonata)

Pre-disposing factor Lightning Symptoms Sudden death of bushes White fan shaped mycelium on the surface of wood beneath the bark Charcoal like encrustation on bark, in advanced stages

Control measures

• Uprooting of affected bushes

• Forking and loosening soil

• Taking 60 x 60 x 60 cm pits 3-4 months ahead of planting

• Keeping them open for aeration

• Spraying dug out soil and pits with 1% copper oxychloride suspension

• Avoiding application of N in the first year of planting

Violet root rot (Sphaerostilbe repens)

Pre disposing factor

• Waterlogging

Symptoms Leaves turn yellow and droop Gradual death of bushes Presence of enlarged lenticels on root bark Roots become inky black/violet Develop rancid odour- vinegar smell Mycelium white, later turns to purple, seen on wood

Control

• Avoid planting in water logged areas

• Improve drainage

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Stem diseases

Collar canker (Phomopsis theae)

• Seen mostly on young tea

• Pathogen invades the stem mostly through open wound

Predisposing factors

• Deep planting

• Planting in gravelly soils

• Mulching closer to collar

• Wound caused by weeding implements

• Fertilizer application close to the collar

• Pegging

• Low moisture status in bark

• Surface watering during dry weather

Symptoms

• Chlorosis

• Cessation of growth

• Profuse flowering

• Canker on stem

Highly susceptible clones

• UPASI 3, TRI 2024

Control measures

• Avoid planting susceptible clones in gravelly soils and drought prone areas.

• Improve organic matter of marginal soils

• Use plants with good root system

Wood rot (Hypoxylon serpens)

Black encrustation (fructification) on stem Affected portion crumbles on gentle pressure Control measures Preventive Avoid pruning during dry weather Curative Rejuvenation pruning

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Leaf disease

Blister blight (Exobasidium vexans)

Favourable conditions for infection :

• Cloudy weather (monsoon months)

• Leaf wetness for 11-13 hrs.

• Relative humidity >60 %

• Temperature 17 to 22ºC

Pathogen entry and symptoms:

Direct penetration through upper surface of leaf Infects only tender leaves and stem (pluckable shoots) Appearance of translucent spot Well developed lesion seen in 2 weeks Lesions sunken on the upper surface and convex at lower surface

• Upper surface is smooth

• Lower surface is first dull then grey and finally pure white

• Affected leaves are distorted- irregularly rolled

• Stem infection leads to goose neck shape, dieback and snapping at the point of infection

• Sporulation occurs after 10-19 days

• Spore discharge period- up to 8 days

• Number of spores ejected in 24 hours - 1.3 million / sq.cm

• Life cycle 11- 28 days

Control measures

Chemicals recommended (Pruned fields):

• Copper oxychloride -Protectant (inhibits germination of spores)

• Triazole fungicides

• Tridemorph (Calixin), hexaconazole (Contaf 5E) and propiconazole (Tilt 25EC)

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General strategy for management of pests

Cultural operations such as plucking, pruning, shade regulation and weed control are manipulated to reduce the incidence of pests. Tea mosquito lays large number of eggs on the broken ends of plucked shoots. Intensive removal of stalks during plucking is recommended to reduce the incidence of this pest. Weeds offer excellent hiding places and serve as alternate hosts for Helopeltis and red spider mites. Growth of weeds and wild host plants in and around tea fields may be controlled and this will help to reduce the incidence of pest. Severity of attack by shot hole borer increases with the age of the field from pruning. Therefore, it is advised to maintain the length of pruning cycles to 4 years in mid elevation areas. Application of higher rate of K₂O to the soil in the first year of the pruning cycle significantly reduces the infestation by shot hole borer.

Biocontrol agents:

Minor status of many of the tea pests is mainly due to the influence of the biocontrol agents. So far, more than one hundred species of predatory and parasitic insects and mites have been reported from the tea estates of southern India. Data are also available on the bioecology of the major parasitoids and predators. An exhaustive list of natural enemies of tea pests is available in Journal of Plantation Crops, 2001, 29 (2): 1-10.

Use of botanicals:

Formulations containing azadirachtin have been found effective against pink and purple mites and caterpillar pests such as flushworms and leaf rollers. Use of these neem formulations are recommended mainly to save natural enemies and to reduce the load of synthetic pesticides on tea.

Use of inorganic compounds,hydrocarbon oils:

Formulations of sulphur is effective against red spider mites. Recently, spray oil from paraffinic base has been found effective against red spider mites. Since this oil does not leave any residues in tea, it is incorporated into the mite control programme in tea.

Integrated pest management (IPM):

During the last one decade, progress achieved to incorporate non-chemical control strategies and to evolve an integrated pest management programme for tea. The package of IPM practices for tea has been presented at the National Workshop, organised by the Directorate of Plant Protection, Govt. of India and the same has been published in the Planters Chronicle April 2002 issue( 98 (4) : 107-125).

Source: http://www.upasitearesearch.org/

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Last updated: 19-06-2008