Learn about the pests that damage jute and its control.
1. Jute Mealybug, Maconellicoccus Hirsutus (Green) (Hemiptera: Pseudococcidae):
Besides jute, this sap-sucking mealy-bug attacks the roselle fibre crop (Hibiscus sabdariffa L.); an important fibre allied to jute, and is responsible for an appreciable decrease in the yield of fibre.
Life-Cycle:
The mated females lay pink cylindrical eggs which are rounded at the ends. The eggs are laid on plants inside the ovisacs and measure 0.3 mm in length and 0.2 mm in breadth. The incubation period varies from 7 to 14 days in different seasons. On completion of the incubation period, the emergence of the nymphs starts from the ovisacs in batches, corresponding with the sequence of egg-laying.
The tiny nymphs crawl out on the host and select a suitable spot to settle down. They are light pinkish and secrete both a white mealy powder and honey-dew. They develop distinctive sex characters after undergoing a few early moultings. The full-grown larva secretes fine white mealy fibres with which it forms a cocoon and then pupates in it.
The females remain wingless, and on maturity, they develop ovisacs in which eggs are laid. The bugs suck sap from the stem and leaves. The female is a rotund, sack-like, light pink creature and measures about 3 mm in length. The males are slender and have a pair of delicate wings.
Scymnus pallidicollis (Coccinellidae) is the most efficient predator and feeds vigorously on the eggs, nymphs and adult females.
Damage:
The nymphs and females feed on the apical parts of a plant which becomes stunted and shows bushy-top symptoms. The petiole becomes shortened, the lamina crumples and the internodal length is reduced, resulting in fibre deterioration and yield reduction.
Prevention and Control:
Spray 1.25 litres of dimethoate 30EC in 625 litres of water per ha.
2. Jute Semilooper, Anomis Sabulifera (Guenee) (Lepidoptera: Noctuidae):
This is a specific pest of jute and is the most destructive in the jute tracts of India and Bangladesh. It is also found in Myanmar and Sri Lanka and in parts of Africa. Only the caterpillars cause damage by feeding on the foliage and being green, they camouflage but are easily noticed when they crawl by producing a loop in the middle.
Life-Cycle:
The pest passes winter in soil in the pupal stage and the moths appear in May-June, when the crop begins to grow in the field. They lay eggs singly on the underside of young leaves; a female may lay more than 150 eggs which look like water droplets. When the weather is warm and moist, the egg stage lasts about two days. The tiny caterpillars, on emerging, start feeding on the apical leaves and buds.
They attain a full length of about 4 cm after 5 moults, in about 17 days. The pupation may take place on the plant or in the soil. In summer, the pupae emerge in about a week, but those, which diapause, spend the entire winter in that stage. The life-cycle is completed in about one month and several generations are completed in a year.
Litomastix gopimobani Mani (Encyrtidae), Tricholyga sorbillans Wiedemann and Sisyropa formosa Linnaeus (Tachinidae) are associated with the larvae of this pest.
Damage:
The attack is severe on half-grown plants which are one metre high. The second generation is the most damaging and sometimes up to 90 per cent of the leaves may be eaten up. Generally, the top 7-9 leaves are damaged and plant growth is adversely affected, resulting in a considerable reduction in the yield of fibre.
Prevention and Control:
(i) The pest can be suppressed by ploughing the infested fields after harvest and thus killing the pupae,
(ii) The caterpillars can be dislodged into kerosenized water by drawing a rope across the young crop.
(iii) Spray 500 ml of fenitrothion 50EC in 500 litres of water per ha. Repeat the treatments three times at 15- day interval from mid-June or at first appearance of the pest.
3. Beet Armyworm, Spodoptera Exigua (Hubner) (Lepidoptera: Noctuidae):
This polyphagous insect is a serious pest of young jute plants and at one time, was a major pest of indigo (Indigofera arrecta) and hence also called indigo caterpillar. Also, it is a minor pest of chillies, onion, brinjal, sweet pepper, gram, linseed, lentil, cabbage, maize, cotton, safflower (Carthamus tinctorius L.), sunflower, etc. Geographically, it is found in Europe, South Africa, America and the Orient. In India, USA, Canada and other countries, it has been recorded as a minor pest of lucerne CMedicago sativa L.) and hence, is also known as the lucerne caterpillar.
The caterpillars feed on leaves, making webs, within which they feed gregariously for 2-3 days. The moths have dark spotted fore wings and white hind wings. They are active at night but remain hidden under various shrubs in the day time. The colour of larvae depends on the crop on which they feed.
Life-Cycle:
The pest passes winter as a pupa, which is enclosed in webbings, forming a rough pupal cocoon. Some of them emerge as moths in February, but a number of them continue in that state till the beginning of the monsoon. A female lays up to 200 eggs in clusters. The eggs are spherical and resemble poppy seeds in shape and size, having lines radiating from the centre.
The egg-clusters are covered with buff hairs. The eggs hatch in 1-3 days and the young caterpillars start feeding in groups. They feed voraciously on the epidermis and also make webs. Within 2-3 days, the gregarious larvae spread out and hide under various shelters, from where they come out in the morning and evening to feed on the leaves.
The larval stage is completed in 15-20 days and the full-grown larvae seek shelter in debris, on the ground. They spin silken webbings and prepare rough cocoons with bits of leaves and other material. The pupal stage lasts 5-7 days and the life cycle is completed in about 30 days. From November onwards, the pest hibernates in the pupal stage. During the active season, a number of generations are completed.
Euplectus sp. (Pselaphidae) is associated with this pest.
Damage:
The damaged crop, on which larvae have fed, gives a webbed appearance. The older caterpillars, which feed in the morning and evening, have a voracious appetite and strip off quite large patches on the foliage. However, the young jute plants, less than two months of age, suffer the most. The early sown capsularis varieties suffer greater losses than those sown later.
Prevention and Control:
(i) The pest can be suppressed by collecting and destroying the egg masses and the caterpillars which are feeding within the webs.
(ii) Spray 625 ml of fenitrothion 50EC in 625 litres of water per ha.
4. Jute Stem Girdler, Nupserha Bicolor Postbrunnea Dutt (Coleoptera: Lamiidae):
Originally, this pest was confined to a number of host plants, among which Sesbania aegyptiaca Gdhaincha) was the most important. However, in the past two decades, it has become a major pest of only one species of jute (Corchorus olitorius L.) and also of mesta, an allied fibre crop. The main damage is caused by the adult beetle while preparing sites for egg-laying on the stem. The geographic distribution is throughout the jute belt in India and Bangladesh.
Life-Cycle:
The female beetle makes two rings by cutting a strip, the space in between the rings being 1.0-1.4 cm. In this area, a slit is made, which reaches as far as the pith, where the beetle deposits one egg. Since a female lays, on an average, 35 eggs, many jute plants are damaged within 2- 3 weeks. The eggs are yellowish and are about 1.5 mm long and 0.5 mm broad. They hatch in 3-4 days and the emerging larvae start feeding and travelling downwards along the central hollow of the stem, feeding on the pith.
The larvae become full-grown in 30-50 days and measure about 1.4 cm. During the active season, the larvae pupate in a chamber made in the hollow of the stem. With the advent of winter, the larvae cut out small portions of the stem in which they encase themselves and diapause.
These encasements are detached from the main stem and when the jute plants are placed under water, they float, carrying with them, the larvae. Thus, the diapausing larvae escape drowning. The females prefer stems of 2.5-5.0 mm in diameter, which are available at different heights of the jute stem, depending on the age of the crop.
The larval stage continues up to the next spring and pupation takes place only after the rains have started. The pupation and the emergence of beetles seem to synchronize with the availability of jute plants. There is only one generation in a year.
The common and important parasitoids associated with the larvae of this pest are Neocatolaccus nupserhae L. and Norbanus acuminatus (Chalcididae)
Damage:
The main damage occurs because of oviposition, resulting in the breakage of fibre length at several places. Thus, both the quality of fibre and the yield suffer. The damage is estimated at 6-30 per cent, being more in younger plants than in the older ones. Not much damage is caused by the feeding of larvae or adults.
Prevention and Control:
(i) In areas where the girdler is a severe pest, the growing of resistant species of jute (capsularis) is useful.
(ii) Mix 25 kg of phorate 10G per ha in the top soil followed by light irrigation.
5. Jute Stem Weevil, Apion Corchori Marshall (Coleoptera: Apionidae):
The jute stem weevil can cause appreciable damage to the early-sown jute or the crop grown for seed. It has been recovered in all the jute-growing parts of India and Bangladesh. The small weevil is only 1.8 mm in length and 0.8 mm in breadth, brown or dull black and has small whitish setae on its body. It bores holes for oviposition with the rostrum in the jute stem and the larvae feeding inside the stem also injure the fibre.
Life-Cycle:
In the active season, the weevils make holes in the stem and lay eggs which are about 0.4 mm in length and 0.3 mm in breadth. A single female may lay as many as 675 eggs during its life-span of about 120 days. The eggs are generally laid at the base of the petiole, in which the larvae bore and damage the top leaves.
In older plants, the weevils prefer to oviposit in the basal region and the lower part of the stem is damaged. The larvae emerge after 3-5 days and start feeding on the surrounding tissues. They are full-fed in 8-11 days when they measure 2.8 mm in length and about 1 mm in breadth. Then, they make a rough chamber in the stem and pupate.
The pupa measures 2.1 mm in length and about 1 mm in breadth. The pupal stage is completed in 4-6 days and the weevil emerges from the pupal case through an exit which is either made by the larva before pupation or by the weevil itself.
Although the adults may live for about 200 days, the normal life-cycle is completed in 15-24 days. A number of overlapping generations are completed during the jute season. The winter is passed in the adult stage and the weevils seek shelter in bushes, shrubs and hedges, and start laying eggs on the new crop next year.
Damage:
The main damage to the quality of fibre is caused by weevils making oviposition holes. A female may make a number of holes before laying an egg and damages numerous stems in her life time. The fields suffering the most are those with nitrogen fertilizer and those which are sown early. The weevil has a number of alternate host plants but the capsularis varieties seem to be relished the most.
Prevention and Control:
(i) The pest may be suppressed by the removal and destruction of infested plants at the time of thinning the crop and by collecting and destroying the stubble after harvest.
(ii) Spray 2.5 kg of carbaryl 50WP in 625 litres of water per ha.