Tea Cultivation - Insect Pest Management

Pest Management

Insect pest management

About 300 species of insects, mites and eelworms are active in tea areas but all of them are not economically important. The pest damage in tea often leads to a significant impact on productivity, in both short and long term, the latter leading to almost total debilitation and thus eroding into the capital asset itself. Since the magnitude of pest infestation varies seasonally depending on altitude, climate and cultural practices therefore an exact assessment of crop loss is very difficult. However, it was estimated anywhere between 6 and 14 %. Pest infestation and quality Despite crop loss, pest infestation also adversely affects the quality of processed tea. Damage by sucking pests like thrips and mites resulted in dull appearance of tea. Teas made from flushworm infested shoots have low levels of extractable solids and high crude fibre content. Liquors obtained from such teas are ‘flat’ and the presence excreta of the larvae perhaps responsible for the deterioration in quality. The severe infestation of flushworm, pink mite, thrips and tea mosquito bug adversely affected flavour and decrease in polyphenolic contents. But tea manufactured from cicadellid Empoasca flavescens Fabr. infested leaves had higher amount of pigments. An increase in polyphenol oxidase activity and total polyphenols was associated with high pigment formation in these teas. Leaf and shoot pests
	Mites Various species of phytophagous mites infest tea. Among the leaf feeders, the red spider mite (Eriophyidae) Oligonychus coffeae Nietner, is very common. O. coffeae breeds throughout the year and may seen any time on the bushes. It can be seen by the naked eye. The population of red spider is found throughout the year in varying intensities.Tea bushes near road side, labour lines especially those covered with dust are usually harbour more number of red spider. Infestation starts along midrib and vein and gradually spreads to the upper surface of mature leaves but when severe it attack young leaves and spread to the undersurface.
They often form a thin web of silken threads and remain protected against adverse weather conditions. The larvae, nymphs and adult mites suck cell sap and the infested leaves turns reddish or coppery and finally brown in colour and defoliation may occur leading to huge loss in crop. A severe attack of red spider is usually followed by the brown and the grey blight. Further, build up of mite population following hail infestation was also observed.The scarlet mite Brevipalpus phoenicis (Geijskes), is also found in Darjeeling. The mites feed on the underside of the leaf particularly around the petiole and sometimes prevents the flow of nutrients into the leaf lamina. Its feeding leads to yellowing of leaves and brownish discolouration of the midrib. Severe infestation results premature defoliation. Control: Dicofol and propargite at 1:200 dilution (low volume sprayer) and 1:400 (high volume sprayer). Sulphur formulations are also used to control mites. Coverage of all leaves on both surfaces with spray fluid is recommended. Thrips Several species of thrips (Thripidae) infest tea and cause heavy damage by feeding on the buds, tender leaves and older tea under plucking. Pruned tea is usually the worst affected. Taeniothrips setiventris Bagnall, is a common thrip and cause considerable damage to tea in Darjeeling hills when new shoots start coming up. Continuous feeding of young leaves by adults and nymphs causes lacerations of the plant tissues. It sucks cell sap which oozes out from the damage leaf. They make small spots in scattered patches and / or in continuous lines on the leaf surface. Two or more corky lines often called sand papery lines appear on either side of mid-rib. Affected leaf become rough and deformed and may curl up. Population of thrips gradually declines with the onset of monsoon. Control: Tea thrips can be controlled by by spraying chlorpyriphos (1:400, HV) or Imida cloprid @125 ml in 400 lit water/ha (high vloum) during non - plucking period. Under plucking condition safer insecticide like Endosulfan (1:400, HV), Cartap hydrochloride (1:1000, HV), Ethotenprox(1:1000, HV) or Neem formulation should be applied. Results obtained from the field experiments show that the effective control of thrips is possible if the control measures are taken up during early or middle of February when the initial attack is noticed. During peak period of incidence (May-June) two sprays at fortnightly intervals should be undertaken immediately after hard plucking. Application of insecticides on foliage, frame and soil around the collar during the early part of the season gives better control of thrips. Black Plucking during infestation helps to remove the population to a great extent. Jassid The Jassid (Cicadellidae) Empoasca flavescens Fabr. commonly known as green fly, is another cell sap feeder occasionally causes serious damage to young and mature tea bushes. Infestation of Jassid causes the margins of the young leaves to turn brown.
	The affected leaves curl downwards with recurved margins and growth hampered severely. This characteristics symptoms is known as rim blight. The attack is restricted to the abaxial surface of the young leaves. The incidence of Jassid used to welcome by the tea planters of Darjeeling. There is a consensus of opinion that the green fly (Jassid) damage improves the quality of tea by increasing the flavour. But there is no definite evidence on the belief. However, if there is even some improvement in flavour, it is doubtful how far the loss of crop is compensated by the improvement of quality of processed tea. Control: Regular plucking removes a large part of the eggs, nymphs and keeps the pest under control. Similar measures on the peak incidence of this pest should be undertaken as mentioned in case of thrips but while spraying care should be taken that the lower surface of the leaves are also properly sprayed.
	Tea mosquito bug The tea mosquito bug (Miridae) Helopeltis theivora Waterhouse, popularly known as ‘tea mosquitoes’ is one of the major pest causing extensive damage in Darjeeling. The nymphs and adults of Helopeltis are the active suckers of sap from buds, young leaves, tender stems and shoots. They feed at early morning, late evening and night hours
On sunny and warm day, Helopeltis takes shelter in lower layer of bush canopy. The insect inject toxic saliva through their needle like rostrum which causes necrosis of the tissues and turn brown first then black and they dry up subsequently. Eggs are laid in tissue of tender stem, mid-rib and petiole of leaves. It was reported that a single first instar nymph of H. theivora could make as many as eighty feeding lesions in 24 hours. Infestation of Helopeltis may become destructive during the cropping season. A total of at least 3 – 4 rounds of rehabilatory spray (zinc sulphate 500 g, boric acid 200 g, urea 500 g in 200 litres of water) can be done in between the pesticidal applications or at weekly intervals.
Control:Similar pesticides as suggested under thrips control should be sprayed during early mornings and late afternoon when these bugs are active. Under sever infestation a round of Synthetic pyrethroid like Deltamethrin (1:2000, HV) should be applied followed up by above pesticide if infestation continues. Before spraying the whole section, about 6 to 10 rows of the bushes covering the outer periphery of the section would be sprayed first and then the operators should move from the periphery towards the section of the centre systematically. Barrier spraying helps to trap the migratory and mobile stages of the population of tea mosquitoes. Spraying should be done after removing the infested leaves by skiffing from the table or by black plucking. The sections prone to Helopeltis attack every year may be pruned or deep skiffed if possible instead of leaving them either unpruned or under lighter form of skiff. Pruning / skiffing in the pest prune areas should be done from the periphery towards the centre where few bushes may be left unpruned. Spray on untouched bushes may be done after three days and then only pruning / skiffing of the bushes can be done. Abundant growth of weeds should not be allowed in Helopeltis prune areas. Aphid The tea aphis (Aphididae) Taxoptera aurantii Boyer de Fonscolombe, is a common pest. The adults and nymphs of this insect continuously suck sap from lower surface of tender leaves along the midrib, tender stem, bud and petioles resulting crinkle leaves curl inwards and growth of the shoot retarded. The field recovering from pruning suffer worst attack of aphids from February onwards. The life history is completed in 5 - 10 days depending on season. Reproduction takes place parthenogenetically. Males are not found during any part of the year. Control: Similar pesticides as suggested under thrips control can be used. Scale insects and mealy bugs Coccoids are sucking pests which attack the foliage, stems and roots of the tea bushes. Their increasing trends have been found throughout Darjeeling. In Darjeeling, Eriochiton theae (Green), Pinnaspis theae (Maskell), Phenacaspis manni Green, Ceroplastes rubens (Maskell), C. cerifera (Anderson), Hemiberlesia rapax (Comstock), Andaspis dasi Williams, Asteroleucanium pustulans (Ckll.) have been recorded as major pests of mature tea. A. dasi caused severe damage to branches of mature tea under cover of mosses. Cultural practices in Darjeeling gardens to keep the bushes unprunned and also the weather conditions are perhaps the main contributing factors for this pest. The coccid and scale infested shoots become unproductive leading to drying up of leaf and fall. When attack lasted long irregular swelling noticed on the branches due to growth of callus inside. Control: Malathion (1:400, HV) shoul be sprayed on the infested branches during non-pluking period. Better control is achived if infested bushes are pruned or deep skiffed and then sprayed. In the plucking season two rounds of drenching spray with appropriate chemical at 15 days interval would generally be sufficient. Caterpillars The bunch caterpillar (Bombycidae) Andraca bipunctata Walker, is occasionally observed in Darjeeling gardens. The destructiveness of caterpillars increases as they grow in age. They remain in clusters during day hours and become active in the night and start feeding ravenously. The branches on which they form clusters are completely stripped of their leaves thereafter they migrate to adjacent bushes. They laid oval shaped yellow eggs in rows on the abaxial surface of the leaves. The life cycle is completed 55- 65 days in March-June.
	The black or sungma caterpillar Lymantria albulunata Mre. found to cause extensive damage to young and mature teas during early 1980s in Sungma tea estate of Darjeeling hills. This is an endemic pest restricted to some particular gardens only. It normally found at an elevation of about 1300 metres and highest population found in May. The female lays eggs in cluster on the abaxial surface of the leaf.
	A lamantriid caterpillar (Orgyia sp. (?) is observed in Darjeeling gardens during February – September. A newly hatched caterpillars are gregarious in habit and feed on the epidermal tissue of the surface of the mature leaves. As a result of damage small hole are formed on the leaf surface. The lamantriid caterpillars attacked both young and mature tea bushes. The full grown and other immature stages of the caterpillar start feeding from the margin of the leaf. In bad infestations the plants may be severely defoliated.
The Darjeeling black hairy caterpillar Euproctis latifascia Walker, is observed in many gardens of Darjeeling hills with limited damage caused by them. It attacks old leaves of young and mature tea. They made small and big perforations on the leaves and occasionally whole leaf is eaten up. Sometimes the young plants in the nursery are defoliated and death occurs. The hairy caterpillars remain concealed underneath the stone, fallen bamboos and lathframes or clod of earth during the day and the damage is caused during night. The body colour of the full grown caterpillar is blackish brown.
	Leaf folding caterpillar such as flushworm (Tortricidae) Cydia leucostoma Meyrick, has become a serious pest of young tea in Darjeeling hills. The larvae immediately after hatching tie up the margins of two or three tender leaves thus forming a protective pocket where the caterpillars live and feed. The affected leaves become rough, thick and somewhat brittle in texture with crinkled appearance.
	The looper caterpillar (Geometridae) Buzura suppressaria Guenee, is also found in Darjeeling tea gardens. The young early instars feed on the margin of the tender leaves while the late instars prefer older leaves. In severe cases of attack caterpillars can completely strip a bush of its leaves and infestation become devastating within a short period. The young looper is dark brown with pale greenish white lines on the back and sides and has a brownish head. The body colour gradually changes to green to brownish grey or dark brown. The life cycle is completed in about 60- 72 days. Young larva of looper is highly mobile and can therefore be carried away to long distances by wind when suspended on silken thread
Control: Endosulfan and phosalone are effective. Synthetic pyrethroids are very efficient to control bunch, sungma and hairy caterpillars. The application rate should be 1: 2000 and 1: 4000 with low volume sprayer and high volume sprayer respectively only for full grown caterpillars and early instars respectively. Bunch caterpillar can easily be controlled by hand collection and destruction as they remain in clusters during day time. The infestation of flushworm can be controlled by hand picking of infested shoots at the time of plucking. Manual removal of caterpillars, pupae will be an easy method in controlling them.
Weevils and beetles Various kinds of weevils attacking tea in India, These weevils devour young and old leaves and if they attack in the nursery or in newly planted field the damage will be serious. Geotragus subfaciatus, attacks tea leaves in Darjeeling hills. Control: Endosulfan and chlorpyrifos are effective against Geotragus sp. Under sever infestation a round of synthetic pyrethroid should be applied.