through the bark and construct galleries within the branches in which eggs are laid. These beetles have symbiotic association with certain groups of fungi called ‘ambrosia fungi’.

Control: The infested dried up branches should be cut back to healthy wood and burned up to kill the alive larvae inside. Cut should be covered by indopasting. Endosulfan, deltamethrin, cypermethrin, fenvalerate are effective.

Beetles

The stem eating beetles in small numbers are found on tea bushes in Darjeeling causing damage to tender stem during March to October. It includes orange beetle Diapromorpha melanopus Lecord and metallic green beetle Chrysolampra flavipes Jacoby.

Control: Spraying with Deltamethrin, cypermethrin, fenvalerate at 1:2000 (low volume) give effective control.

Root pests

Nematodes or eelworms

Plant parasitic nematodes of tea which are found in the soil and affect the root system of the plant. Infestation of root-knot nematodes Meloidogyne incognita Kofoid & White, M. hapla Chitwood and M. javanica Treub, are very destructive to young plants in the nursery. The invasion of roots by eelworms stimulates the root tissues to abnormal growth with the result that galls or root knots are produced and normal differentiation of cells into vascular tissues is virtually blocked and transport of water, solutes are impaired. Therefore, nutrient imbalance is created, photosynthetic rate is reduced and symptoms of nutrient deficiency are expressed causing a general decline in the vigour of the plant, which ultimately become more susceptible to various kinds of stresses. Premature flowering and fruiting some times noticed in case of severely infested plants. The resultant symptoms in the aerial parts are stunted growth, pallor of the leaves and later wilting. Tea plantation infested with nematodes are characterised by patches of unthrifty teas having weak frames. In the nursery, though clonal plants and seedlings are equally affected by root knot nematodes, but clonal plants can withstand nematode attack comparitively better than seedlings since they possess greater amount of roots.

Control: No specific method ensuring complete eradication of nematodes in the nursery is available but some precautionary measures can be taken to reduce the intensity of attack to seedlings and cuttings. However, nursery soils may be treated with systemic granular formulations such as carbofuran 3G, phorate 10G @ 1 g / sleeve / 1 kg of soil. Second application at the same rate after one month of first application should be given. Watering should follow after each application for quick absorbtion of chemical. Phytotoxicity was noticed when applied at higher dosages of granular nematicides. Basamid G, a broad spectrum soil sterilant, @ 20, 30 and 40 gram / sq. m soil was also found very effective against eelworm.

White grubs

Holotrichia sp. normally causes damage to young tea around the collar region which is debarked in the form of a ring or in patches. In such cases the mulch materials during late February or early March should be kept in between rows of tea plants instead of keeping them around the collar, so that the adult cockchafer do not lay eggs near the collar region in the mulch. The early instar grubs feed on the tender roots of grasses and on dry decomposed leaves. The later instars feed on the young tea plants in the collar region. Cockchafer beetles emerge between March and June in north eastern region of India. They mostly affect plants in new clearings. But damage is not uncommon to three to four year old plants. This insect is abundantly found in Darjeeling hills.

Control: In the affected area, the surface soil around the collar of each plant may be loosened and treated with endosulfan / chlorpyriphos solution at a rate of 1:300. After 15 to 21 days of first application, second application at the same rate may be given.
The root mealy bugs Pseudococcus theaecola (Green), Crisicoccus sp., damage roots of the tea bushes in Darjeeling and can be controlled by soil drenching with endosulfan / chlorpyriphos at 1:300 dilution after soil forking of the collar region.

of the young seeds taken place. In case of mature seeds which can not be punctured through the shell, the feeding is restricted to the pericarp only.

Control: Endosulfan or Imidacloprid may be sprayed during July-August. If necessary, second and third spray may be done during February-March and May-June respectively.

Seasonal abundance of pests

Since insects are poikilothermic (cold blooded), their body temperature varies with the surrounding temperature and so they are especially strongly influenced by climate and weather. Temperature, precipitation, humidity, wind speed and other climatic variables can directly influence pest by affecting their rate of development, reproduction, distribution, migration and adaptation. In addition, indirect effects can occur through the influence of climate on the insects’ host plants, natural enemies and interspecific interaction with other insects

The incidence of aphids, thrips and red spider mites was observed to be correlated with maximum-minimum temperature, humidity and rainfall. In general, the month of February and March appeared to be most favourable for incidence of aphids Toxoptera aurantii Boyer de Fonscolombe, followed by a greater incidence in July. The mite population was found to be very much weather dependent. The population of red spider mites mainly occurs in late winter and summer months.

The population of jassid found on tea bushes throughout the year. The population reaches peak in May - June in plains and June - July in Darjeeling.

The tea mosquito Helopeltis theivora Waterhouse, breeds all the year round but it numbers fluctuate. The population during cold dwindles down and it reappear in February - March from the residual population. Serious infestation seen during June to September when bushes virtually cease to form shoots and there may be total loss of crop. The infestation subsided in November and the adults are rarely found in December.

Pesticide residue in tea

Recent focus on pesticide residues on processed tea has led issuance of Maximum Residue Limits (MRLs) on a group of pesticides by different producing and consuming countries and various International agencies. A time frame has been prescribed to achieve these limits. Most of the pesticide after spray on the canopy of the tea plant is retained on the leaf surface and constitute the initial deposit of the plant along with transpirative flows. Many of the organophosphate compounds penetrate into the leaf surface rather quickly (Systemic). The application of acaricides and other insecticide on tea are usually carried out soon after plucking. These chemicals consequently are deposited on the mature maintenance foliage and also on the shoots which are in different stages of growth. The weight of these immature shoots increases over a period of 6 - 14 days, depending on the plucking interval. Therefore, the pesticides applied on such shoots undergo a growth dilution. In other words, the weight of a bud increases during the plucking interval and this helps in bringing down the residues of pesticides if any on a weight by weight basis (mg/kg). The immature buds by the time attain the size of pluckable shoots (2/3 leaves and a bud), the residue of applied pesticides on them will be either nil or very low. In Darjeeling, the residue level of malathion, quinalphos and fenvalerate are found to declined more than 90 % in 7 days after spraying and the percentage caused by growth dilution may be little less than 45 %. Further, between application of a pesticide and the consumption of the tea, a considerable amount of the pesticide present in green leaves is lost at the time of processing at high temperature. Generally, 30 - 60 % of pesticide residues are lost in the manufacturing process. Degradation in this stage is primarily due to evaporation and thermal decomposition. It has been reported that the higher the vapour pressure, the greater the degradation during processing. It was also observed that rainfall, evaporation, biodegradation and photolysis are some of the ways in which pesticide residues are lost. Sensitivity of pesticides to light is an important factor which determines their residues on tea. In an experiment conducted in Darjeeling, no residue of monocrotophos after 4 hours of its application was detected during dry and wet seasons. The residues of malathion, fenvalerate, dimethoate on 5th day after application in dry season were found below the MRLs established by various organisations and countries. Further, in case of quinalphos it was on 7 th day after application. While in case of dicofol the residue on 7th day during wet season was found below MRLs but it was higher in dry season. Researchers have also observed in Darjeeling that the residue of organophosphate and chlorpyriphos in processed tea on 5th day after application at the recommended dose (1:400) are well below the prescribed MRLs. They further observed there is no necessity to discard first plucking when cypermethrin is applied at the recommended dose (1:4000). Loss of pesticide residue also takes place in storing and with the passage of time between processing of tea and use of the same. When tea is infused with boiling water, pesticide residues contained in tea are partly degraded by high temperature and partly by dissolving in the liquor which will be consumed. Generally, only those pesticides with high water solubility may potentially be transferred to the tea cup in significant amounts. If the applied chemical is not easily soluble, more residues may remain on the spent tea and less in the infusion.

The ‘half life’ of insecticides on tea varies greatly. It was observed in an experiment conducted in Darjeeling, pyrethroid pesticides had very similar half life in dry and wet seasons while the half life of organophosphate vary from 13 hrs to 26 hrs in dry season and 6 to 21 hrs in wet season. The half life of quinalphos in wet season was recorded high (2.73 days) while in dicofol it was 0.4 and 1.2 days in dry and wet seasons respectively.