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SUSVEG-Asia Brinjal IPM

Brinjal flower

Brinjal (Solanum melongena L)
Family : Solanaceae

The vegetable brinjal, Solanum melongena L. (Solanaceae), is often referred to as eggplant or aubergine in other regions of the world and is grown for its fleshy fruit.  Two crops are typically grown per year in South Asia and because fruits can be harvested every week farmers are provided with an assured income and resource-poor consumers have access to a much-needed, nutritious vegetable, in the summer months when other vegetables are in short supply. 

In India alone over 500,000 ha of brinjal is cultivated per annum with yields of typically 20-40 tonnes/ha/crop.  In Bangladesh vegetables are grown on 2% of the available agricultural land and yield 4% of the produce, unlike rice that uses 72% of the land and yields 51% of the food by weight.  Brinjal is by far the major vegetable representing some 41% by weight of all vegetables produced, occupying 19% of the land used to cultivate them.  

As with every crop farmers have to cope with a range of pests, diseases and crop nutrition issues in order to produce a healthy brinjal crop.  Brinjal is affected locally by whitefly (Bemisia tabaci), ash weevil, (Myllcerus discolour), red spider mite (Tetranychus curcurbitae) and little leaf disease (transmitted by jassids) and soil pathogens such as bacterial wilt (Ralstonia solanacearum) are increasing in prevalence.  In some areas of Gujarat parasitic plants such as orobranche are endemic.  Nevertheless, the most serious pest of brinjal is without doubt the brinjal fruit and shoot borer, Leucinodes orbonalis, a lepidopterous pest whose larvae are well protected from pesticides and natural enemies once they have entered the fruit or young shoots. 

Farmers have depended entirely on insecticides to control of L. orbonalis but the sustainability of this approach is in question as farmers in some areas of Northern India and Bangladesh are finding that even daily applications do not provide effective control.  Indeed farmers in some areas of Bangadesh are applying up to 180 applications of insecticide a year at a cost of $1200/ha/yr, constituting 40-50% of cultivation costs in 2003.  For this reason the project prioritised research effort on this key pest and much of the IPM package developed was concerned with this issue, although technologies for control of other potential pests and diseases based on work by other groups were incorporated. 

Brinjal fruit and shoot borer, Leucinodes orbonalis

The female moth lays eggs individually on the shoots of young brinjal plants. The small larvae that emerge soon eat their way into the tender growing shoots where they are protected from larval parasitoids and natural enemies such as ants and beetles. The feeding activity of the larvae causes the young shoots to droop in a characteristic manner

Adult L. orbonalis moth
Infested brinjal shoot
Female L. orbonalis moth
Brinjal shoot infested with larvae

As the brinjal plant develops and begins to produce fruit the female moth preferentially lays eggs on the fruit into which emerging larvae burrow. Several larvae can be present in one fruit at a time, depending of the fruit’s size.  As the larvae burrow into the fruit they block the hole with excrement or frass so preventing predators entering attacking them.  Only the parasitic wasp, Trathala flavo-orbitalis (Hymenoptera: Ichneumonidae) has an ovipositor long and strong enough to reach the larvae and lay eggs in them.  Project researchers at BARI found that T. flavo-orbitalis can have a significant effect on control of the larvae of L. orbonalis but only when farmers stop applying insecticides, because unlike the pest T. flavo-orbitalis is highly sensitive to insecticides.  The highest incidence of T. flavo-orbitalis occurs between July and December with infestation of larvae in shoots ranged from 12 to 30% and in fruits from 7 to 25%.  Fortunately, T. flavo-orbitalis is a parasitoid of rice leaffolder, Cnaphalocrocis medinalis, as well and so there is no need to augment the population with artificially reared insects because natural populations rapidly colonise non-pesticide treated crops.  Indeed in surveys conducted by BARI researchers the highest levels of natural control of L. orbonalis were found in areas with the lowest use of insecticide and achieved by T. flavo-orbitalis

Remove and destroy infested shhots
Remove and destroy infested fruit
Remove infested shoots by hand
Remove and bury infested brinjal fruit
Shred infested crop residues
grafted brinjal - root stock resistant to bacterial wilt
Remove and shred crop residues
Grafted brinjal - root resistant to bacterial wilt

Crop Hygiene

Crop hygiene is particularly important in areas of intensive cultivation, and in particular where related crops are cultivated over long periods of time.  Infested shoots and fruits should be removed by hand from brinjal fields.  Both can act as sources of future infestation.  Similarly, at the end of a woody crop residues are often collected and stored for use as firewood.  However, these residues contain larvae which emerge the following spring and lay eggs in newly established nurseries.  Ideally crop residues should be shredded or burnt before the next crop is planted in the same way that fields are ploughed to reduce populations of soil borne pests and diseases.  Alternatively, nurseries should be located as far from crop residues as possible.  In general insecticides should be avoided for as long as possible in order to preserve the natural enemies and predators that act to reduce the incidence of L. orbonalis and secondary pests such as T. curcurbitae which are only a problem because of application of insecticides kills the predators that keep their populations in check. 

Mass trapping for control of brinjal borer

As the name suggests control by mass trapping involves catching the insects in a baited trap.  In this case the bait is the female-produced sex pheromone used to catch the adult male moth.  The lure is highly attractive to male moths and specific to the target species.  The purpose of this activity is to reduce the chances of female moths finding a mate so that she is unable to produce viable offspring.  Research by AVRDC suggests that female L. orbonalis only mate once and form other research we know that even delayed mating can significantly reduce the number of viable eggs female moths can produce (fecundity).  Nevertheless, in order to catch enough male moths to have an impact on size of the next generation of damaging larvae it is important to know what constitutes the best quality lures and traps, the minimum area that can be treated and where to place them in a crop (height and density).  These were some of the issues that project researchers investigated in order to provide farmers with a cost-effective and efficacious system that would control the pest.  Indeed this is one of the very few examples of the successful use of mass trapping of Lepidopterous pests to achieve significant levels of control appropriate for use by smallholder farmers.

The Lure

The pheromone lure is composed of two active compounds (E)-11-hexadecenyl acetate and (E)-11-hexadecen-1-ol in a ratio of 100 : 1.  Farmers would normally purchase these from reputable suppliers already impregnated into polymer dispensers.  Ideally the dispensers should have a field life in excess of two months with an optimal loading of 3mg.  The ratio of the compounds is critical, any more than 3% of the minor component and attractiveness is compromised and a complete absence of the compound also reduces catch significantly.  The compounds are relatively stable to sunlight but their high molecular weights mean that typical rubber septa used for other Lepidopterous pheromones, such as Helicoverpa armigera, are not best suited for this pheromone and polyethylene vials were found to significantly increase release rate and hence attraction. 

The trap

A range of traps designs have been found to be suitable for L. orbonalis and although the best catches were obtained with flat sticky discs, they were not practical for farmers and water traps prepared from plastic bottles are recommended, although in India dry funnel traps are inexpensive and readily available in the market.

Setting up pheromone trap
Dry funnel trap
Preparing a water trap
A dry funnel trap
Pheromone lure in funnel trap
Promoting mass trapping at farmer meeting, Gujarat
Lure inside funnel trap
Promoting traps at farmers' meeting, Gujarat

Water traps work best when a small amount of detergent is added to reduce the surface tension and the lure is positioned 1 cm above the water level to encourage contact.  Dry funnel traps require less maintenance but good quality plastic bags are essential because they are found to split after some time in the field. 

Trap placement

The optimal trap density is 100 per ha (40 per acre) and control can be achieved in 0.5 ha plots.  The timing of trap placement is entirely up to the farmer.  Project researchers found that while higher yields are obtained if the traps are placed out some after transplanting nevertheless the farmer will achieve benefits even if the traps are placed into field of mature crop with a high incidence of infestation.  However, there is a 2 to 3 week delay before the incidence is reduced significantly because of the high larval population already present.  Traps should typically be placed at crop height or just above to achieve the optimum catch and traps should be evenly spaced in the field (5 m spacing).  Mass trapping not completely remove infestation but can reduce damage to less than 20% from a mature crop with 70% damage and works more effectively if insecticide application is stopped.  Using a reduced number of traps will still achieve some effect and encouraging neighbours to use them will benefit both farmers. 

Bacterial wilt

Soil pathogens can be major constraints to brinjal production, particularly in periods of heavy rain.  In Bangladesh a technique of grafting resistant rootstocks has been developed by IPM CRSP researchers.  This technique involves rearing both wild-type resistant and cultivated susceptible seedlings until they have two true leaves (15 to 21 days.  Make a V-shaped vertical cut in the rooted wild-type resistant plant approximately 1cm above the soil level and placing the susceptible seedling into the split after cutting the seedling in a similar manner to remove the root system.  The two plants are then held together with a plastic peg for a few days and then released.  Farmers who have come forward for training in the technique from BARI have set themselves up as entrepreneurs to sell the seedling to their neighbours at a good profit.  Grafted plants can be cropped for up to 1.5 months longer than conventional crops with significant increases in yield.  The technique is also effective with tomato plants. 

Farmer's friends

Unlike cotton, little effort is made to encourage farmers’ friends in brinjal.  Indeed, at first sight there appears to be little insect activity on the crop, in contrast to rice, for example, which teams with life.  Certainly, the larval stage of the major pest, L. orbonalis, is well protected inside either stem or fruit of the plant.  Nevertheless, it is vulnerable to attack by predators in the egg, and adult stages and by larval parasitoids, such as T. flavo-orbitalis, mentioned above, in the larval stage.  Generalist predators such as ants, ground beetles, ladybirds, spiders and related natural enemies and parasitoids are all important for preventing minor pest species from achieving economic importance, notably grasshoppers (e.g. Oxya nitidula, Poekilocerus pictus), whitefly, Besimia tabaci, thrips, (e.g. Frankliniella schultzei, Thrips apicatus, T. tabaci), and jassids (Empoasca devastans, Hishimonus phycitis).  To encourage such species farmers should set aside small areas of land to cultivate flowering weed species and in particular those that provide alternative food sources for ‘farmers friends’ such as nectar.  Bird perches should not be necessary in brinjal but would be of assistance to species such as drongo’s, flycatchers and bee-eaters that prefer to rest above the canopy level. 

Predatory dragonfly
Predatory spider
Farmers' friend dragonfly
Farmers' friend - spider
Predatory ladybird larva
Predatory ladybird adult
Farmers' friend - Ladybird larva
Farmers' friend - Ladybird adult

Minor pests and diseases

Little leaf is a minor disease and one that is best controlled by removing infested plants and either burning or burying them.  The symptoms are easily recognised by a profusion of small leaf growth.  Failure to remove infested plants will allow the infestation time to spread to neighbouring plants. 

Little leaf disease
Weeding - a family affair
Little leaf disease in brinjal
Weeding - a family affair
Ash weevil - minor pest
Flower beetle - minor pest
Ash weevil - minor pest
Flower beetle - minor pest

Effective weed management is very important for a healthy vegetable crop and although most farmers conduct up to 5 to 6 hand-weeding operations a season significant cost-savings can be made by weeding at critical times in the crop cycle, typically twice at 15 to 20 and 35 to 40 days after sowing.

Brinjal grey or ash weevil, Myllocerus subfasciatus (Coleoptera: Curculionidae) is a widely distributed insect.  Adults are leaf feeders and can cause significant local damage.  Larvae feed on roots which results in widespread wilting and can lead to premature death of mature plants.  Female M. subfasciatus lay up to 500 eggs over a period of three months, however, the eggs are laid in the soil and rarely seen.  Farmers locally control the pest using phorate or carbofuran (1 kg a.i. per ha) but this should be avoided where possible. 

Adult flower beetles such as Oxycetonia versicolor are large brilliantly coloured, day flying beetles that are readily recognised by farmers.  They are principally pollen feeders.  The larvae develop in organic matter in the soil and while some do infest roots they are seldom of any economic importance to brinjal producers.

Root knot nematode can be a significant problem, although this only becomes apparent when the root nodules are observed after harvest.  Nevertheless, where fields have a history of nematode problems farmers IPM CRSP recommends the use of decomposed chicken manure (3 tonnes/ha) although project researchers did not find this treatment efficacious with tomato plants, whereas the use of marigold plants (Tagetes erecta) or cold water extracts prepared from them was highly effective. 

Epilachna larva
Epilachna adult
Epilachna larva
Epilachna adult
Epilachna - leaf damage
Epilachna - fruit damage
Epilachna - leaf damage
Epilachna - fruit damage

Epilachna beetle, Epilachna vigintioctopunctata Fabricius (=Henosepilachna vigintioctopunctata) (Coleoptera: Coccinellidae) causes economic damage in some areas of South Asia.  Adult and larvae are polyphagous, feeding in a characteristic scraping manner on tomato, potato and brinjal leaves, in particular.  Adult females can lay between 120 to 180 spindle-shaped eggs in groups of 10 to 20.  The white larvae are characteristic with brown, branched spines over the body.  The larvae pupate on the leaf surface.  Pupae are yellow with the anterior devoid of spines.  Adults emerge after 7 days with 12 to 28 spots on their elytra.  Because the life cycle takes between 17 and 50 days, they have the potential to cause considerable economic damage but rarely do.  Nevertheless, project researchers at TNAU found, for the first time, evidence to suggest that Epilachna beetle fed on brinjal fruit pericarp and mesocarp resulting in considerable economic loss for the farmer concerned.  The reason why the beetle fed on fruit was thought to be related to the use of high nitrogen fertilizer inputs, though this was not confirmed.  The feeding resulted in mature fruit in which seed were exposed and no market value.   High temperatures and low relative humidity have an adverse effect on development and while the beetles can be controlled with insecticides balanced fertilizer inputs and natural control should ensure that they are not required. 

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