Each tea growing areas has its own distinctive pests and diseases though several of them might have been recorded from more than one region. Number of pests and diseases associated with tea plants in an area depends on the length of time for which it is cultivated in that area. More than one thousand species of arthropod pests and nearly 400 pathogens are known to attack tea all over the world, though only about 300 species of insects and mites and 58 pathogenic fungi are recorded from tea in India. Crop loss due to pest and diseases varies between 15 and 20%. Magnitude of the losses is bound to be higher today in view of the increased production and productivity besides the variations in climatic conditions.
Mites are serious pests of tea and they damage the green tissues of leaves, thereby reducing the photosynthetic efficiency resulting in yield reduction. Infestation leads to discoloration of leaves. Most of the species occupy the under surface of the leaves but a few prefer the upper surface also.
Pink mite, Acaphylla theae (Eriophyidae: Acarina):
Important mite pest of tea in southern India causes considerable damage. During early stages of attack leaves turn pale and curl upwards while severe infestation leads to brownish discolouration. Pink mites attack tender crop shoots where “Aassam” hybrids are more susceptible. Eggs are shiny, globular in shape and lay singly on the under surface of the leaves. Eggs are hatches in 2-3 days; there are two nymphal stages and they are white in colour. Population builds up initiates in November/December and attains peak in February/March and declined during May/June. Life cycle completed in 6-9 days.
Purple mite, Calacarus carinatus (Eriophyidae: Acarina):
Damaged leaves characterized by the coppery brown discoloration; presence of numerous white cast skins of the mites along with the live mites; purple mites are prevalent on the under surface of mature leaves; adults are very small, spindle shaped, purple colour; fringed body with five longitudinal white waxy ridges on dorsal side, young ones moult three times; incubation period ranges 3-5 days with two nymphal stages while total developmental period was 6-11 days.
Pale mite, Acaphyllisa parindiae (Eriophyidae: Acarina):
Adult mite is pale white and dorsoventrally flattened; broadly rounded anterior end and tapering posterior end; seen on the under surface of the mature foliage; incubation period 2-3 days, nymphal stages 4-6 days; development completed in 6-9 days.
Scarlet mite, Brevipalpus australis (Tenuipalpidae : Acarina):
Symptoms of attack first appear on either side of the midrib and gradually spread to the entire leaf; feeding leads to brown discolouration of leaves and severe infestation leads to defoliation; adult mite is scarlet red in colour and obovate in shape; reproduction is by parthenogenesis. Eggs are bright red, elliptical, laid in clusters; incubation period is 7-10 days; developmental stages include three legged larva, protonymph and deutonymph and each developmental stage is followed by a quiescent stage; life cycle completed in 30-36 days
Yellow mite, Polyphagotarsonemus latus (Tarsonemidae: Acarina):
observed on young leaves, especially on the top two to three leaves and the bud. Leaves become rough and brittle and corky lines or patches on the surface. Females are yellowish and bigger than the males and they carrying the “female nymphs” on their back. Eggs large, obovate, flattened at the bottom; eggs hatches after 27-32 hours and life cycle completed in 3-5 days.
Control measures (of above listed mite species) include monitoring the field population by regular assessments, regulation of the shade trees as per recommendation and enhancing the populations of natural enemies (phytoseiid mites, predatory thrips and cecidomyiids) in tea ecosystem. Application of spore suspension of the entomopathogen, Parcilomyces jumosotroscus (UPASI sthain) Mycomihc @ 1.5 kg/ha or neem formulations 0.03-0.15% Aza @ 1000 ml/ha or 1% @ 200-400 ml/ha or 5% @ 100-200 ml/ha or sulphur formulations 80% @ 1000 g/ha or dicofol 18.5 EC @ 1000 ml/ha or ethion 50 EC @ 750 ml/ha are recommended. While using power sprayers use a spray volume of 300-350 l/ha or 400-450 l/ha with hand operated knapsack sprayer.
Red spider mite, Oligonychus coffeae (Tetranychidae: Acarina):
Important mite pest causes considerable damage during the past few years. Infestation starts along midrib and veins further spreads to the entire upper surface of leaves. Due to feeding, the maintenance foliage turns ruddy bronze and infested fields distinct even from a long distance. Severe infestation leads to defoliation. Adult female elliptical in shape, bright crimson anteriorly and dark pruplish brown posteriorlym. Mites spin a web of silken threads on the leaf. Eggs reddish, spherical, provided with a small filament. Incubation period is 4-6 days, before hatching becomes light orange colour. Developmental stages include six legged larva, protonymph and deutonymph. Each developmental stage is followed by a quiescent stage and life cycle completed in 10-14 days.
Control measures of red spider mites can broadly classified as cultural, biological and chemical control methods. Cultural control measures include monitoring the population dynamics by regular field assessment, shade/weed management and removal of alternate host plants (Bidens, Ageratum, Conyza, Crassocephalum, etc). Biological control measures include allowing the build up of natural enemies (phytoseiid mites and coccinellid beetles (lady bird beetles) in tea ecosystem and application of spore suspension of the entomopathogen, Verticillium lecanii @ 1.5 kg/ha in the evening hours when humidity is more. Certain chemicals were recommended for control of red spider mites which include spray formulations of sulphur 80% @ 1000 g/ha, lime sulphur @ 1:40. If mite persists spray any one of the acaricides like dicofol 18.5 EC @ 1000 ml/ha, ethion 50 EC @ 750 ml/ha, fenpropathrin 10 E @ 500 ml/ha, combination of dicofol and ethion 500 ml each and dicofol and quinalphos @ 500 + 350 ml are effective against the pest. While using power sprayers use a spray volume of 350-400 l/ha or 450-500 l/ha with hand operated knapsack sprayer. Care must be taken to thoroughly drench the maintenance foliage and chemicals should be applied only after plucking.
Tea mosquito, Helopeltis theivora (Miridae: Heteroptera: Hemiptera):
Adults and nymphs punctures the plant tissues with needle like rostrum and suck the sap from buds, young leaves and tender stems. Punctures appear as reddish brown spots and due to intensive feeding, leaves curl up, badly deformed and remain small. Shoots dry up and crop loss is near total in response to severe incidence. Adults black in colour, red thorax, black and white abdomen and greenish brown wings. They were active early mornings and late evenings, more in moist shaded areas. Five nymphal stages and development completed in 15-17 days. Its incidence was high during July to December and low between January and June.
Monitoring the infestation level in the field, black plucking, weed control and removal of stalks containing tea mosquito eggs are important cultural control methods. Allowing builing up of egg parasitoid (Erythmelus helopeltidis) in the tea ecosystem is a recommended biological control measure. Certain molecules, endosulfan 35 EC @ 1000 ml/ha, quinalphos 25 EC @ 750 ml/ha, chlorpyrifos 20 EC @ 750 ml/ha, fenthion 80 EC @ 200 ml/ha, quinalphos 25 EC + dichlorvos 76 EC @ 750 + 250 ml/ha recommended for control of tea mosquito. Spraying is suggested in the early mornings or evenings when these bugs are active.
Lygus bug, Lygus sp. (Miridae: Heteroptera: Hemiptera):
Adults and nymphs injure the tender plant parts. Mouth parts are piercing and sucking type. Feeding punctures appear as reddish brown necrotic spots. Symptoms of damage are similar to that caused by Helopeltis attack and it can be controlled as detailed for Helopeltis.
Tea aphid, Toxoptera aurantii (Aphididae: Homoptera: Hemiptera):Colonies seen on tender shoots of young plants and bushes recovering from pruning. Adults and immature stages suck the sap from tender shoots. Due to feeding leaves curl up and stunted shoot growth observed. Attack on young buds delays the recovery of pruned bushes. Colonies of aphids consist of dark brown alate and apterous adult females and nymphs. Population is more from January to April and low during June/July. Monitoring the population in the field with yellow pan water trap, maintenance of regulated shade and manual removal of infested shoots reduce the population to an extent. Aphids are largely regulated by biocontrol agents where larvae of the syrphids and the coccinellids are major predators followed by three species of aphidiid parasitoids. If pest persists application of neem formulations 0.03-0.15% Aza @ 1000 ml/ha or 1% @ 200-400 ml/ha or 5% @ 100-200 ml/ha or spore suspension of the entomopathogen, Paeceilomyces fumosoroseus @ 1.5 kg/ha in the evening hours when humidity is more are recommended.
Mealy bug, Nipaecoccus viridis (Pseudococcidae: Homoptera: Hemiptera):Feeds on the young shoots and its severe infestation leads to defoliation. Adult female soft bodied, oval, flattened, dark brown, 2.5-3.0 mm long, female laid a large number of eggs, hatches out in 7-10 days with a total developmental period of 15-20 days. Monitoring the field population and manual removal of infested branches controls Mealy bug population. If pest persists Quinalphos 25 EC @ 500 ml/ha or dimethoate 20 EC @ 500 ml/ha is recommended. Addition of non ionic wetting agent (5 ml/10 l of water) will be helpful in achieving better control.
Brown bug, Saissetia coffeae (Coccidae: Homoptera: Hemiptera):Mature scales are: hemispherical in shape and deep brown in colour; occurs on leaves and tender stems; females are sedentary; adult males are winged forms; Eggs are seen under the scale; crawlers disperse and attach themselves with tender plant parts after hatching. Brown bugs naturally regulated by the parasitoids, Encyrtus infelix and Coccophagus cowperi and it can be controlled as recommended for Mealy bug.
Green scale, Coccus viridis (Coccidae: Homoptera: Hemiptera):Observed on tender stems and leaves; females yellowish green in colour and oval in shape; reproduction by parthenogenesis, female lay 600 eggs; eggs hatch out immediately after deposition; three nymphal instars lasting 4-6 weeks; adults live for 2-5 months. It can be controlled as recommended for mealy bug.
Root mealy bug, Dysmicoccus sp. (Pseudococcidae: Homoptera: Hemiptera):
Attack the roots of young tea plants in nurseries.
Tea Jassid, Empoasca flavescens (Cicadellidae: Homoptera: Hemiptera):
Adults and nymphs suck the sap from tender leaves; leaves curl downwards, gradually turn brown and dry up; adults are yellowish green and measure 2.5-2.75mm long; eggs inserted singly into the leaves; incubation period varies from 6-13 days; development completed in 8-15 days according to the temperature. Plucking removes a large part of eggs and nymphs and it can be controlled as recommended for mealy bug.
Tea Thrips, Scirtothrips bispinosus (Thripidae: Thysanoptera):
Prefers young leaves and buds; continuous feeding causes lacerations which appear as streaks; leaf surface becomes uneven and curled; feeding marks on the buds later appear as two parallel lines; attack more pronounced in the fields recovering from pruning; leads to inordinate delay in tipping and consequent crop loss; adults characterised by their brown abdomen, Incubation period is 6-8 days; egg hatch into larva, two larval instars, creamy white in color, prominent eyes; prepupa and pupae are found in the leaf litter and soil; adults emerge from the pupae after 3-5 days; weak fliers, dispersal and migration is helped by wind; build up starts by Nov/Dec. reaches peak in Feb/March or April/May. Monitoring the population in the field with yellow sticky traps and maintenance of regular shade besides the natural enemies like Anthocorids and predatory thrips can reduce the population. Suggested to apply the spore suspension of the entomopathogen, Verticillium lecanii @ 1.5 kg/ha in the evening hours when humidity is more. Certain chemicals were recommended for control of thrips; quinalphos 25 EC @ 750 ml/ha; dimethoate 20 EC @ 500 ml/ha; endosulfan 35 EC @ 1000 ml/ha; quinalphos 25 EC + dichlorvos 76 EC @ 750+250 ml/ha. Spray should be targeted to the shoots on and below the plucking table, and also the side.
Caterpillars: Large group of insects injurious to tea;
flushworms, leaf rollers and tea tortrix are common caterpillar pests commonly seen in first year fields recovering from pruning. Make leaf nests by webbing the leaves, one above the other, feed from inside. Populations seen in large numbers during August to December.
Flushworm, Cydia leucostoma (Tortricidae: Lepidoptera):
Larva is brown in colour 1 cm long; enters into the bud by making a small hole, ties up the margins of growing bud and form a case; feeds on the upper epidermis of leaves; affected leaves become rough, crinkled and leathery; adult moth very small, less than 1cm long blackish brown in colour; eggs are pale yellow and laid singly on the undersurface of mature leaves; incubation period 4-5 days, five larval instars; larva takes 19-25 days for development inside the leaf case; pupal period varies from 8-10 days; moths were active during morning and evening hours; Control measures include manual removal of infested shoots. Flushworm is naturally regulated by the larval and pupal parasitoids; if pest persists spray neem formulations 0.03-0.15% Aza @ 1000 ml/ha or 1% @ 200-400 ml/ha or 5% @ 100-200 ml/ha or spray the spore suspension of the entomopathogen, Paecilomyces fumosoroseus @ 1.5 kg/ha in the evening hours when humidity is more.
Tea tortrix, Homona coffearia (Tortricide: Lepidoptera):
Caterpillars make leaf nests by webbing the leaves, one above the other, using silken threads, and feed from inside; adult moth is brown coloured, bell shaped; eggs are laid in masses, incubation period 6-8 days; larvae are greenish in colour and about 2 cm long; larval period last for 20-30 days; pupal period ranges from 9-15 days. Control measures are same as for flushworm.
Tea leaf roller, Caloptilia theivora (Gracillariidae: Lepidoptera):
Young caterpillar first mines into the leaf; older larvae roll the leaves from tip downwards, feed from inside; normally, young leaves are preferred; adult moth is very small, with narrow wings; eggs are deposited on the undersurface of leaves; larva hatch out in 2-3 days; larval period is 14-20 days; pupal duration 7-14 days.
Pyralid leaf webber, Ereboenis saturata (Pyralidae: Lepidoptera):
Larva feeds on older leaves from the upper surface; leaving the lower epidermis, the skeleton of leaves; the caterpillar webbed together the individual leaves by silken thread; feed gregariously from inside the web.
Looper caterpillar, Buzura suppressaria (Geometridae: Lepidoptera):
Young caterpillars feed on young leaves and mature larvae prefer older leaves; they made series of small holes along and a little away from the margin; in severe cases of attack, tea bushes completely denuded; female deposits upto 200 eggs in batches on the tree trunks; incubation period 7-10 days; on emergence, caterpillars suspend by silken threads and get dispersed by wind; larvae dark brown with pale greenish white lines on the back and side; on the leaves, they move like leeches; after 4-5 weeks, they pupated in the soil for a period of 3-4 weeks; pupa brownish, 2-2.5 cm long, life cycle completed in 8-10 weeks.
Twig caterpillar: Ectropis bhurmitra (Geometridae: Lepidoptera):
Young caterpillars feed on young leaves and mature larvae prefer older leaves; in severe cases of attack, whole leaves are eaten off, leaving the midrib; adult large pale grey wings and slender body; eggs are bluish laid in clusters; covered by a mass of buff coloured hairs; incubation period is 7-10 days; mature larvae are dark brown 4.5 cm long; while resting the larvae are closely resemble a dry twig; larval period is completed in 3-4 weeks and pupated in the soil; pupae are 1.5-2 cm long and reddish brown colour; life cycle is completed in about 5 weeks.
Blue striped nettle grub, Latoia lepida (Limacodidae: Lepidoptera):
Feeds the maintenance foliage; grubs green in colour with three pale blue longitudinal stripes; full grown grubs measure 3-4 cm long; eggs are flattened, laid in clusters of 10-30; single female lays more than 500 eggs and hatch in 6-8 days.
Saddle backed nettle grub, Thosea cervina (Limacodidae: Lepidoptera):
Larvae feed on the leaf tissue on the under surface; severe cases of infestation completely strip off the leaves; adult moth is dark reddish brown; mature larvae are 4 cm long, greenish colour with three brown markings; central marking is saddle shaped, other two are look like pear; larvae pupate in the soil; pupae are dark brown, globular and resemble tea seeds.
Fringed nettle grub, Darna nararia (Limacodidae: Lepidoptera):
Caterpillars scraping on the under surface of leaves; during severe outbreak, the leaves are completely eaten off; pale brown adult moths are active at night; eggs are oval, flattened, shiny and laid singly on leaves; incubation period is about a week; larvae are about 1.5 cm and pale green in colour; larvae moult five times and larval duration is five weeks; pupated in the soil for three weeks.
White banded nettle grub, Thosea recta Hampson (Limacodidae: Lepidoptera):
Young larvae scrape off the under surface of the leaf; mature larvae eat large portions of leaves; adult moths are grayish brown and measure about 2.5 cm across wings; larvae are green in colour with a silvery white band on the dorsal side; brown oval cocoons are seen attached to leaves or twigs.
Large jelly grub, Belippa lalaena (Limacodidae: Lepidoptera):
Larvae eat off large portions of mature leaves; grubs are pale bluish, 1.5 cm long, rounded and resemble a bulb of jelly; larval period is about 2 months; cocoons are whitish, rounded and attached to bushes. Control measures are identical as suggested for caterpillars.
Large Faggot worm, Eumeta crameri (Psychidae: Lepidoptera):
Infest the older leaves and bark; in the pruned fields, damage will be severe; male moths are reddish brown with wings; male moths are reddish brown with wings; females are devoid of wings and legs; winged males are mate with grub like females; female lay 500 eggs inside the case; incubation period is 10-15 days; young caterpillars construct silken bags, covering with bark and dry twigs; larval duration is 9-10 months; before pupation, the bag is suspended from the bush; larva pupated inside the closed bag; male moth emerges out but the female remains inside the pupa.
Red slug caterpillar, Eterusia aedea virescens (Zygaenidae: Lepidoptera):
Prefers mature foliage; by severe attack, the bush frames become naked; adult moths are brightly coloured in hues of black and pale yellow; eggs pale white in colour and oval in shape; incubation period is 10-12 days; caterpillars resemble nettle grubs and moves like slug; larva is brick red colour with six rows of tubercles on the body; larva ejects a viscous fluid through these pores as a defensive mechanism, when disturbed; five larval instars completed in 4-5 weeks; caterpillar spins a pale yellow colour cocoon for pupation; adult emergence takes place after 3 weeks.
Lobster caterpillar, Neostauropus alternus (Notodontidae: Lepidoptera):
Commonly seen in new clearings and nurseries; completely devour all the leaves from a small plant; forewings of moths are grayish white with few reddish brown spots; eggs are whitish, finely sculptured and laid in small clusters; incubation period is 5-10 days; the black caterpillars are grotesquely shaped and resemble dry leaves; larval period is 3-4 weeks; pupated inside a wooly cocoon; adults emerge after 10-14 days.
Cut worm, Spodoptera litura (Noctuidae: Lepidoptera):
Attack the maintenance foliage; made irregular holes on the tea leaves by feeding; adults have white hind wings; forewings are grayish brown marked with silvery lines; eggs laid in clusters, hatched in 3-4 days; larvae are dull olive green in colour and feed for 3 weeks; pupated in the soil for one week.
Red borer, Zeuzera coffeae (Cossidae: Lepidoptera):
Usually, young stems are bored by the caterpillars; as the larva grows, the tunnel is also extended; holes are made at intervals to eject the excreta and wood particles; tunnel may run even up to root; moths have white wings with many black spots; eggs are laid like beads on a thread; caterpillars emerge in 10 days; they suspend themselves by silken threads and get dispersed; larvae bore into young stems; larvae tunnel downwards, devouring the woody parts, especially the pith; tunnels are extended to thicker branches; mature larva is about 3.5 cm long and purplish brown or reddish brown in colour; larval duration is 4-5 months; pupated in a special chamber for a month.The affected branches may be cut to sound wood. The larvae may be killed in situ by pouring a strong solution of an insecticide like endosulfan or quinalphos by using an ink filler and plugging the holes.
Hepialid borer, Sahyadrassus malabaricus (Hepialidae: Lepidoptera):
Young caterpillars bore into the stems; excavate long cylindrical tunnels; eating of bark and sapwood resulted in cankers; top end of the tunnel opens into cankers; feeding takes place at night; it can move forward and backward with equal ease; attacked bushes can be easily located by the frassy mat, formed of powdered wood and silk, hanging near the holes; they have grey forewings with faint mottlings; male produce sharp, pungent, mustard like smell by the scent glands; eggs are broadcast by the female in flight; a few succeed in tunneling the tea stems; caterpillars made very long galleries extend up to roots; mature larva is pale yellow, pencil thick and 6-10 cm long; Larval duration is 10 months; pupated in the lower part of the tunnel; pupal period lasts for 3-5 weeks. Control measures same as for red borer.
Shot hole borer, Euwallacea fornicatus (Scolytidae: Coleoptera):
Female beetles construct galleries in stems; leads to branch breakage and consequent crop loss; grubs and adults feed on the fungus, Fusarium bugnicourtii growing in the galleries; female beetle are black, 2-2.5 mm long with strongly sclerotised body; eggs are laid singly inside the gallery, three larval instars; female lays upto 45 eggs, male female ratio 1:8; population reaches high levels during April, May, July, October and December; all life stages are seen throughout the year;
SHB is managed in an integrated way with the following control measures:
Cultural control (medium type of pruning in SHB infested fields, post prune spraying with any one of the recommended insecticides, application of N and K2O at 1:2 in the pruned year, assessment of SHB infestation level at the end of second year or beginning of third year using the sta ndard sampling method), biological control methods (mid-cycle control measures in the third and fourth years if the average percentage of infestation in the new wood is at or above 15%, two rounds of entomopathogen spray (B. bassiana WP) during May end, July and October) and chemical control (two rounds of recommended insecticide spraying during April and December.
White grub: Holotrichia sp. (Melolonthidae: Coleoptera):
Larvae eat away the roots of young plants; at times they gnaw the bark of stems near the ground causing a ring barking effect; adults are brownish in colour; eggs are deposited in the soil; incubation period 12-18 days; larval period is 8- 10 months; pupal period lasts for 3 months. Pre heating of nursery soil and check the organic manure/compost thoroughly for eggs or grubs or pupae before their application. Addition of systemic granular insecticides in the nursery soil; soil application of endosulfan 35 EC at the concentration of 1: 500 (20 ml of the chemical in 10 l of water); soil around each bush may be treated with 1 litre of the spray fluid; application may preferably be carried out with a soil injector or soil around the plant loosened and the diluted chemical has to be applied; use knapsack sprayer after removing the nozzle; application has to be repeated after one month.
Leaf eating beetles, Mimela xanthorrhina (Scarabaeidae: Coleoptera):
Beetles prefer mature foliage; adult beetles are metallic green in colour. Application of endosulfan 35 EC @ 1000 ml/ha or quinalphos 25 EC 750 ml/ha recommended for its control.
Leaf eating weevil, Myllocerus sp. (Curculionidae: Coleoptera):
Application of endosulfan or quinalphos will be effective.
Grasshoppers & crickets, Grasshoppers: Orthacris incongruens and Orthacris robusta (Pyrgomorphidae: Orthoptera):
Migrate to tea only when their natural weed hosts are eliminated and feed on mature tea leaves.
Cricket, Brachytrupes portentosus:
Destructive pest in tea nurseries. Application of endosulfan or quinalphos will be effective.
Termites, Odontotermes spp. (Isoptera):
Considered only as secondary pests and these are scavengers of dead and moribund wood.
Termites: Microcerotermes sp. (Isoptera):
Damage tea bushes in north-east India while Glyptotermes dilatatus, Neotermes greeni and Postelectrotermes militaris attack tea in Sri Lanka.
Tea leaf miner, Tropicomyia theae (Agromyzidae: Diptera):
Leaf mining fly inserts the eggs into the leaves; emerging larvae make meandering tunnels on the leaves; l arvae are cylindrical, tapering anteriorly and truncated posteriorly; pupate inside the tunnel at the leaf margin; developmental period is a month.
Sewing blight: Orasema sp. (Eucharitidae: Hymenoptera):
Wasp lays eggs on tea leaves; oviposition marks appear as a line of punctures; there is no serious threat.
Root knot nematode, Meloidogyne javanica (Heteroderidae: Tylenchida):
Causes severe galling of roots of mature tea bushes; leaves become smaller in size, yellowish in appearance, growth is retarded; eggs and larvae are relatively large and the stylets are unusually long in larvae and females. Application of carbofuran 3 G @ 25 g/bush immediately after pruning and repeat the application after 3 months. Application of neemcake @ 2 kg/bush is also suggested.
Tea diseases can be categorized in to three classes on the basis of the plant part that infected by the pathogen, viz., root, stem and leaf diseases.
Most common root diseases are red root disease (Poria hypolateritia) brown root disease (Fomes noxius) and black root disease (Rosellinia arcuata). Primary root diseases are common in the areas previously under jungle, spreads through soil or by root contact and leads to death of bush. Chlorosis and drying without defoliation are initial symptoms of the primary root diseases. Apart from these primary root diseases, secondary root diseases like charcoal stump rot (Ustulina zonata), violet root rot (Sphaerostilbe repens) and Diplodia root rot (Botryodiplodia theobromae) are also common. Primary root diseases have been controlled by soil drenching with systemic fungicides like carbendazim, tridemorph, hexaconazole (0.5% solution) and application of biocontrol agents such as Trichoderma sp. and Gliocladium sp. in the planting pit (200 g/pit).
Black root disease (Rosellinia arcuata)
First identified root disease of tea, black, wooly mycelium on root surface and at collar while 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 and spreads rapidly in damp weather. Removal of surface mulch around 10 meters is suggested followed by drenching the soil with Dithane M 45/Captan 30 g/10 litres of water. Avoid soil rehabilitation.
Red root disease (Poria hypolateritia):
Fast spreading and slow killing pathogen; 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 and spreads mostly by root contact. Alternate hosts are Coffee, Grevillea, Albizia and Erythrina.
Brown root disease (Fomes noxius):
Common in low elevation area; slow spreading and quick killing pathogen; soil encrustation, which cannot easily be washed off; mycelium tawny brown resembling sambar skin; Wood turns soft and spongy and 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 and alternate hosts are Coffee, Grevillea, Albizia and Erythrina.
Xylaria root disease (Xylaria sp.):
Roots covered by black, ribbon like mycelial strands; Extensive necrosis of feeder roots; causes stress for nutrients and moisture which resulted in high casualty soon after drought. Alternate hosts are Grevillea, Indigofera and Erythrina.
Control measures of root diseases:
Phytosanitary measures include isolation of infected area by taking trenches of 1.2 m deep and 45 cm width. Uprooting and burning the bushes in situ are warranted. Rehabilitate soil with Gautemala grass or thornless Mimosa. Soil treatment with tridemorph or hexaconazole 0.5% @ 100 ml/hole punched at every square foot. Soil treatment can be carried out after six months of planting during April/May or November/December. At the time of planting incorporation of biocontrol agents like Trichoderma species or Gliocladium virens @ 200 g per planting pit is recommended.
Secondary Root Diseases:
Charcoal stump rot (Ustulina zonata):
Lightning is a pre-disposing factor for charcoal stump rot. Sudden death of bushes, white fan shaped mycelium on the surface of wood beneath the bark and charcoal like encrustation on bark seen in advanced stages are the symptoms. Uprooting of affected bushes, forking and loosening soil and taking 60 X 60 X 60 cm pits 3-4 months prior to planting and keeping them open for aeration are suggested. Spraying dug out soil and pits with 1% copper oxychloride suspension and avoiding N application in the first year of planting is suggested as control measures.
Diplodia root disease (Botryodiplodia theobromae):
Commonly seen in low and mid-elevations area and debilitation of the bushes casused due to lack of starch reserves caused by continuous hard plucking and pruning the bushes soon after rush crop, prolonged soil moisture stress and damage due to pests and diseases. Weak appearance of frame and presence of unhealthy leaves, failure of bushes to recover after pruning, dieback of new shoots and presence of white powdery spots with black centres on root surface are the symptoms of Diplodia root disease. Control measures improve the health and vigour of the plants which include carrying out pruning at the right time, adopting proper plucking standards and adequate manuring and timely plant protection measures taken.
Violet root rot (Sphaerostilbe repens):
Water logging is the predisposing factor. Symptoms due to violet root rot are 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 and white colour mycelium, later turns to purple, seen on wood. Avoid planting in water logging areas and improved drainage controls the violet root rot in tea.
Collar canker (Phomopsis theae):
Observed mostly in young tea and pathogen invades the stem through open wound. Predisposing factors are 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 and surface watering during dry weather. Chlorosis, cessation of growth, profuse flowering and canker on stem are the symptoms of collar canker. Certain clones are highly susceptible to collar canker (UPASI-3 & TRI-2024). Preventive measures include avoid planting of susceptible clones in gravelly soils and drought prone areas, improving organic matter of marginal soils and using plants with good root system. Removal of affected portion by pruning to healthy wood and application of copper fungicide or spore suspension of biocontrol agents like Trichoderma and Gliocladium to cut ends are the curative measures.
Wood rot (Hypoxylon serpens):
Black encrustation (fructification) on stem and affected portion crumbles on gentle pressure. Pruning during dry weather conditions should be avoided and rejuvenation pruning is suggested as curative measure.
Branch Canker (Macrophoma theicola):
Cancerous growth around the longitudinal wounds on the branches of tea bush. This fungus is a weak parasite affecting the bushes damaged by hail. Control measures are to cut off the affected branches and spraying any of the systemic fungicides (Tridemorph, hexaconazole and/or calixin) at 0.5 % (50g in 10L) over the infected portions.
Leptothyrium die-back (Leptothyrium theae):
Common in higher altitudes, noticed in fields recovering from pruning; pathogen enters through the prune cuts dieback of shoots below the cut ends; infected branches snap off easily. Application of copper oxychloride & linseed oil paste on cut ends, soon after pruning prevents the disease.
Blister blight (Exobasidium vexans):
Favourable conditions for infection are cloudy weather (monsoon months); continuous leaf wetness for 11-13 hours coupled with relative humidity >60% and temperature between 17 to 22oC. Direct penetration of pathogen through upper surface of leaf; infects only tender leaves and stem (pluckable shoots); appearance of translucent spot and well developed lesion seen in 2 weeks. Lesions sunken on the upper surface and convex at lower surface where upper surface is smooth while 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 and spore discharge period extends upto 8 days. Number of spores ejected in 24 hours is 1.3 million/sq.cm and the pathogen completes its life cycle 11- 28 days. Chemical fungicides such as copper oxychloride as protectant (inhibits germination of spores), tridemorph (Calixin), hexaconazole (Contaf 5E) and propiconazole (Tilt 25EC) are recommended for blister blight control in both pruning and plucking fields. Spraying schedules are issued for adoption in south Indian plantations.
Grey blight (Pestalotiopsis theae) and brown blight (Glomerella cingulata):
Pathogen gains entry through wounds and more prevalence in shear harvesting fields during monsoon, stripping, inadequate blister blight control leads to wounds. Spraying of mancozeb at 0.3% (30 g in 10 litres of water) or carbendazim or thiophanate methyl 0.05 % (5 g in 10 litres of water using hand operated knapsack sprayers at 10-15 days interval could be followed to control such diseases. Affected bushes should be thoroughly drenched with the fungicide suspension. The spray volume can be adjusted between 175 and 300 litres per hectare.