Tea Cultivation - Insect Pest Management

Pest Management III

Alternative to targeted pesticides

The use of chemical pesticides can be minimised by integrating it with other available methods of control.

Biological control
Numerous biocontrol agents are active in tea fields exerting a natural regulation of several pests. A considerable number of natural enemies of pests of tea have been identified and some of them have been proved capable under ideal conditions of keeping the pest populations below economic threshold levels.





a. Chrysoperla	b. Robber fly	c. Orange dragon fly
d. Adult ladybird beetle (Coccinella)	e. Assassin bug sucking the juices from larva	f. Grub ladybird beetle
g. Mantis	h. Wasp	i. A mud Wasp's nest packed with larvae
j. Spider	k. Wolf Spider	l. Damsel fly

There are two methods in the study of indigenous natural enemies:
i. Identification and augumentation and conservation of natural enemies.
ii. Mass rearing of natural enemies in laboratories and releasing against pest at frequent intervals.

A single ladybird can devour an entire colony of thrips or mites in a day. Collection and subsequent release of ladybirds in badly infected areas has given excellent result. The areas have shown almost complete recovery within 45 days followed by prolonged mite free period. Similarly a spider can kill five hoppers in a day. The aphid, Toxoptera aurantii is naturally controlled by syrphid, coccinellid and hemerobiid predators and aphidiid parasitoids. The braconid, Apanteles aristacus Nixon, is the principal parasitoid of Cydia leucostoma. Sympiesis dolichogaster Ashmead, is the major natural enemy of leaf roller, Caloptilia theivora. Biological methods of control are not available at present for all pests affecting tea. However, they are in the process of evolution and refinement.

Cover crop and living mulches

It may provide habitat for natural enemies of insects, mites and nematodes. Pests may be supressed through antagonistic or allelopathic effect, or by preferential attraction to the cover crop over the desired crop.

Microbial agents

It includes bacteria, fungi, viruses, protozoa, and nematodes that are pathogenic or antagonistic to pest species, including insects, plant pathogens and weeds. Pathogens can cause epizootics in pest populations, especially caterpillars. Encouraging results were obtained with introduction of Bacillus thuringiensis (Bt) against Cydia leucostoma. Bt is safe for human beings but its crystal protein produces a fatal endotoxin in the gut of the target caterpillar pests. A fungus Paecilomyces tenuipes (Peck) Samson was recorded in tea estates of Darjeeling parasitising pupal stage of various Psychid pests (Basket worm) of tea during early June to late October. B. bassiana, an entomopathogenic fungus isolated from membracid bug, a shade tree pest, was tested against Helopeltis in Darjeeling provided 49 % control by spraying 20 % suspension for two rounds at 15 days intervals.

Pest resistant clones

It would provide inexpensive, environmentally sound, and highly effective way to avoid pest problems. Even low levels of resistance are important since the need for other control methods can be reduced. Different cultivars of tea with varying growth habits differ in their resistance, tolerance and susceptibility to pests.

Botanical insecticides

These are derived from extractions, pressing, infusions, pulverizing, etc and they come from any plant part. The fact they are plant derived, however, does not distinguish them from other pesticides by virtue of their use, mode of action, chemistry, formulation toxicity safety, efficacy, marketability, or overal utility.

Neem has been found to have multifarious properties like antifeedant, repellent, toxicant, growth inhibitor, antiovipository etc. The bio-efficacy of neem oil (NO) and neem seed kernel powder (NSKP) against sucking pests have been observed in a field trial conducted in Darjeeling.NO and liquid soap at 1% concentration offered best control followed by NSKP 100 gm treatment. The average cost benefit ratio was 1: 2.13. It was also observed various plants exhibiting insecticidal activity which could be effectively utilized for the control of specific type of pests. The antifeedant properties of the extracts derived from the aerial parts (leaves and stem) of Artimisia vulgaris Linn. Urtica dioica Linn. Polygonum runcinetum Ham. and Eupatorium glandulosum Linn. which are at home in Darjeeling hills were evaluated in the laboratory against bunch caterpillar, Andraca bipunctata. The maximum antifeedant action was exhibited by the extract of A. vulgaris followed by P. runcinatum, U. dioica and E. glandulosum. The problem associated with much-hailed botanicals and biopesticides is their varying degrees of sucesses in the field situation. Actually while a sector of scientific community advocates in favour of them reporting their superiority in laboratory trials, others demonstrated their inefficiency in many-a-field trials.

Cultural control

This, probably the most economical and widely applicable method of pest control. In tea, routine cultural operations such as mulching, plucking, pruning, manuring, regulation of shade and drainage which increase the vigour of the bush plays a predominant role in suppression of pests. Infestation by mites and thrips is seen more in tea fields devoid of shade. The heavily shaded and moist areas will be damaged more by tea mosquito bug. Leaf folding caterpillars during plucking can be manually removed. A few rounds of black plucking reduce the incidence of thrips, Helopeltis etc. Weeds serve as alternate hosts for many tea pests. Effective weed control assumes greater significance in the management of tea mosquitoes. Further, the insect pests are also removed by plucking, skiffing and pruning. These operations are assumed to strongly affect the population of insect pests on new shoots. Balanced nutrition helps improves vigour of plants to withstand pest attack.

Semiochemicals, including pheromones, allomones, kairomones

Another approach for controlling pests is to modify their behaviour by exploiting their natural chemical communication or feeding cues. Semiochemicals are non-toxic behaviour modifying a mixture of chemical compounds released from exocrine glands of insects such as sex pheromones, used by insect females to attract their mates, and antifeedants which may be based on the compounds produced by plants. The pheromones, in general, do not find a place in pest control in tea in India. However, in many moth species the females releases pheromones (odours) and in response males fly up wind to find them. For some species these compounds have been identified and synthesized. Such pheromones have been used mainly for monitoring populations, for disrupting mating, for mass trapping, and for lure and kill.

The allelochemicals such as kairomones and allomones produced by plants and herbivores may help in enhancing natural enemy activity and may find a role in integrated pest management (IPM) in tea as well.

Insect growth regulators (hormones) can be effectively employed for adverse modification of the normal growth and behaviour of tea pests. Growth regulators like dimilin found to be biologically effective to hinder the normal growth of caterpillars and full grown larvae of bunch caterpillars fails to pupate. The chitin inhibitor, diflubenzuron had been field tested for the management of Cydia leucostoma of tea.

Oil, soap and other fatty acids

These are effective and have less impact on human health and wild life than synthetic organic chemicals. The spray of lemongrass (Cymbopogon citratus and C. nardus) oil and other vegetable oil had good control over some tea pests.

Integrated Pest Management (IPM)

It comprises strategies aimed at minimising pest damage through the careful integration of available pest control technologies. IPM is a pest management system that in the context of associated environment and the population dynamics of the pest species, utilizes all suitable techniques and methods in as compatible a manner as possible and maintains pest populations at levels below those causing economic injury. It is not simply the juxtaposition or superimposition of two control techniques (such as chemical and biological controls) but integration of all suitable management techniques with the natural regulating and limiting elements of the environmen.
In IPM system when pesticide application is inevitable the following tips are important to keep the residue below MRL.

• Keep vigilance on pest incidence. Proper identification of pest, their developmental stages, site of attack, damage symptoms etc are necessary for selection of right pesticides. In case of combined infestation of red spider, pink and purple mites, recommended acaricides may be used. But combined infestation with scarlet mites, sulphur should be avoided as it has no effect on scarlet mite. However, recommendations issued by the Tea Research Institutes should be consulted for the right choice of pesticide and their dosage.

• Monitoring of the incidence and build up of pests, for example, tea mosquitoes, green fly, red spider, can show initial build up in the month of January-February in north east India. If initial build up is not controlled, repeated rounds of spraying can not be avoided during cropping season.

• Biological information - critical time for taking up control measures and economic threshold will have to be determined. Damage threshold limits have been established in India for mite pest (Banerjee, 1971b), in China for tea looper, tea Jassid, pink mite, leaf rollers, tussock moth and the black aphid (Chen and Yin, 1988) and in Sri Lanka for the plant parasitic nematodes (Gnanapragasam and Herath, 1989).

• Identification of alternate hosts of pests and where possible use them as trap crop. Plant species which is preferred for oviposition by particular insect can be utilised as trap crop.

• Apply pesticides only when it is absolutely necessary.

• Proper supervision during spraying is important. Often, in absence of supervision, the operators may tend to over apply the pesticides at places and complete the job/task expeditiously. Such application may bound to carry residues in plucked leaves. Supervision is therefore must.

• Soil stirring during the cold weather reduces the incidence of caterpillars, thrips, termites, cockchafer grubs etc.

• Bush health and hygiene is prerequisite for good crop protection. It may be of little use to adopt control measures if, for example, the soil is not prepared well or soil fertility is low or unbalanced. Many crop pests affect primarily weakened plants. It is therefore, important to aim for a healthy bush by proper tillage, planting of proper clone at the right time, appropriate spacing and providing sufficient water/moisture and nutrients. A healthy bush can compensate pest damage by growing new shoots or spreading up the growth of undamaged parts.

• Alkaline washing of pruned bushes reduces pest incidence. The alkaline solution (washing soda 6 kg, quick lime2-3 kg and water 100 litre) may be kept for overnight and strain by using cheese cloth. The strained solution may be applied to the frame by using a hand operated sprayer fitted with nozzle size 40.

• Use of pesticides on rotation. Synthetic pyrethroids should not be used repeatedly or at frequent intervals.

• Allow a minimum gap of eight to ten days between insecticide/acaricide application and plucking.

• Use of conventional sprayer is preferable.