Tea Pests and Their Control
(Note: The author is not an expert. Please take expert advice before using any Pest Control Method.)
Losses due to pests are estimated at 7-10 per cent of the total tea crop; of this, three-quarters is due to the red-spider. In individual gardens or in localized areas, it can at times be 15-25 per cent. The important pests in north-east India are mites, termites, scales, aphids, etc., whereas in south India, the shot hole borer, thrips and mites are the major pests.
Mites are responsible for more and recurring losses in tea than all the other pests taken together. Amongst the mites, the red-spider and scarlet mite are the most important; the two other mites, purple mite and pink mite, may also cause severe damage to tea in some situations. Small populations of the white mite have also occasionally been recorded on seed-trees. In south India, the pink mite and the purple mite are the worst enemies of tea causing economic losses, closely followed by the red spider. The red-spider mite is the most damaging amongst the major pests of tea in north-east India. It attacks the upper surface of the leaves; when the attack is severe it might even shift to the lower surface. The mite spins a fine web over the leaf-surface and its sucking produces red spots which collectively may become so numerous as to give the whole leaf a brick-red appearance. Where attacks are serious, polysulphide sprays are effective against the mites, but to kill the eggs, lime-sulphur is needed. New organic acaricides, such as Chlorobenzilate and Kelthane sprays, can provide adequate control.
Scarlet mite causes serious damage to both young and mature tea in many districts of the north-east India. The mite may be bright scarlet or orange. It sucks the leaf sap, causing brownish discoloration of the affected parts. When the infestation is severe, the leaves may fall and the tender stems present a broomstick-like appearance. Lime-sulphur emulsions containing 0.05 per cent of Chlorobenzilate and 0.037 per cent of Kelthane give effective control.
The purple mite occurs in south India and attacks especially the upper surface of the mature leaves. The affected leaves develop a coppery discoloration on the upper surface which later turns purplish-bronze; such leaves dry up. Chlorobenzilate, Malathion or lime sulphur (1 in 40 parts of water) is effective controls. Yellow mite is occasionally found on isolated bushes in north- east India. It is parchment-colored with a clouded dorsal stripe. It prevails during cloudy weather and attacks only the young leaves, thus ruining the flush. Two applications of lime- sulphur preparation containing 22-26 per cent polysulphide control the mite.
Pink mite has in recent years caused considerable and widespread damage to the young tea in dry weather in Assam. It is also one of the major acarine pest complexes of tea in south India. The affected leafy portion becomes pale, leathery, with the veins and margins becoming light pink and thickened. Infested bushes become stunted.
The tortrix has occasionally caused considerable damage in north-east India. It spins silken threads which contract on drying, drawing the leaf-edges together, thus forming a protective pocket where the caterpillars live and feed. Three or four sprays of DDT (0.1%) give sufficient control.
Several species of thrips are found in the main tea-growing areas. They affect only young and tender leaves and unfolding buds. The affected leaf has rough appearance with minute, brown spots in scattered patches or in continuous lines. The regenerative phase of growth after pruning is the period when the damage is the most and a severe attack may delay the tipping operation. In Assam, this can interfere with the valued second- flush yield.
The jassid or green fly is widely distributed in all the tea-growing districts. The adults and nymphs suck and sap from the under surface of growing shoots; the nymphs cause more damage. The affected leaves become uneven, turn brown and dry up. DDT as spray (0.1%) and emulsion are effective.
The shot-hole borer is the most destructive pest in south India. The bark-boring scolytid beetle is rare in north-east India but of late it has been found to infest large areas of tea in this region. The female bores into the branches and excavates extensive and typical galleries about 2 mm in diameter. Mid-cycle application of Deltamethrin (Decis 2.3 EC at 500 ml/ha) or Fenvalerate (Sumicidin 20.0 EC at 500 ml/ha) reduces the attack of shot-hole borer and increases the yield.
The red borer of tea is a widely distributed pest of tea and causes considerable damage to young and nursery plants. The larva bores into the stem. The leaves wither and dry out even though the branch is unbroken. Introducing paradichlorobenzene in the ejection holes and then plugging the holes kill the larvae. Termites are troublesome pests that can kill mature bushes and sizeable trees. At least 15 per cent of crop is annually lost due to termite damage in north-east India. Dressing the topsoil with Dieldrin (2.25 kg/ha) after final preparation of the beds prevents termite attacks.
Tea is also susceptible to several species of scale-insects, metallic-green beetles and several species of parasitic nematodes.