Learn about the pests that damage winter vegetables and its control.
1. Cabbage Caterpillar, Pieris Brassicae (Linnaeus) (Lepidoptera: Pieridae):
The cabbage caterpillar is world-wide and is found wherever cruciferous vegetables are grown. It is a serious pest of cabbage, cauliflower, knol-khol and it may also attack turnip, radish, sarson, toria (Brassica campestris) and other cruciferous plants.
Damage is caused by caterpillars only. When full-grown, they measure 40-50 mm in length. The young larvae are pale yellow, and become greenish-yellow later on. The head is black and the dorsum is marked with black spots. The body is decorated with short hair. The butterflies are pale white and have a smoky shade on the dorsal side of the body.
The wings are pale white, with a black patch on the apical angle of each fore wing and a black spot on the costal margin of each hind wing. The females measure 6.5 cm across the spread wings and have two conspicuous black circular dots on the dorsal side of each fore wing. Males are smaller than the females and have black spots on the underside of each fore wing.
Life-Cycle:
In the Indo-Gangetic plains, this pest appears on cruciferous vegetables at the beginning of October and remains active up to the end of April. From May to September, the pest is not found in the plains but breeding takes place in the mountains. The butterflies are very active in the field and lay, on an average, 164 yellowish conical eggs in clusters of 50-90 on the upper or the lower side of a leaf.
The eggs hatch in 11-17 days in November-February and 3-7 days in March-May. The caterpillars feed gregariously during the early instars and disperse as they approach maturity. They pass through five stages and are full-fed in 15-22 days during March-April and 30- 40 days during November-February.
The larvae pupate at some distance from the food plants, often in barns or on trees. The pupal stage lasts 7.7-14.4 days in March-April and 20-28 days in November- February. The butterflies live for 2.5-12.5 days and the pest breeds four times during October-April.
The larvae of this insect are Parasitized by Apanteles Glomeratus (Linnaeus) (Braconidae) in the natural populations.
Damage:
The caterpillars alone cause damage. The first instar caterpillars just scrape the leaf surface, whereas the subsequent instars eat up leaves from the margins inwards, leaving intact the main veins. Often, entire plants are eaten up.
Control:
(i) Handpicking and mechanical destruction of caterpillars during early stage of attack can reduce infestation, and
(ii) Spray one litre of malathion 50EC in 250 litres of water per ha. Repeat spraying at 10-day intervals if necessary. Do not spray the crop at least one week before the harvest.
2. Diamondback Moth, Plutella Xylostella (Linnaeus) (Lepidoptera: Yponomeutidae):
This world-wide moth is a serious pest of cauliflower and cabbage, but also feeds on many other cruciferous, solanaceous and liliaceous plants, all over India.
Damage is caused by the caterpillars which, in the earlier stages, feed in mines on the lower side of cabbage leaves and, in the later stages, feed exposed on the leaves. When full-grown, the larvae measure about 8 mm in length and are pale yellowish green with fine black hair scattered all over the body. The moths measure about 8-12 mm in length and are brown or grey, with conspicuous white spots on the fore wings, which appear like diamond patterns when the wings lie flat over the body.
Life-Cycle:
This insect is active throughout the year. Yellowish eggs of the size of pin-heads are laid singly or in batches of 2-40 on the underside of leaves. A female may lay 18-356 eggs in her life-time. The eggs hatch in 9.1, 3.7 and 2.5 days at 13.9, 17.9 and 23.4° C, respectively.
The newly hatched caterpillars bore into the tissue from the underside of leaves and feed in these tunnels. At first, their presence is detected only from the blackish excreta that appear at the mouth of each tunnel, but in the second instar, the mines become more prominent. In the third instar, the caterpillars usually feed outside the tunnels.
The larvae of the fourth instar feed from the underside of leaves, leaving intact a parchment-like transparent cuticular layer on the dorsal surface. The larvae are very sensitive to touch, wind or other physical disturbances and readily feign death. They become full-grown in 16.6, 14.3 and 8.6 days at 17, 20 and 25°C, respectively.
Before pupating, the larva constructs a barrel-shaped silken cocoon which is open at both ends and is attached to the leaf surface. The pupal stage lasts 4-5 days at 17- 25°C and the moths may live for as long as 20 days. The life-cycle is completed in 15-18 days during September-October and there are several generations in a year.
Larval stage is parasitized by Voria ruratis Fab., Itoplectis sp. (Ichneumonidae), Apauteles sicarius (Braconidae) and Tetrasticus sokolowskii (Eulophidae). Brachymeria excarinata Gahan (Chalcididae) is associated with pupa. A larval-pupal parasitoid, Diadrumus collaris (Gravenhorst) (Ichneumonidae) is also found to be associated with this pest.
Apauteles plutellae Kurdyumov effectively checks the population of diamondback moth on cabbage in Gujarat and Karnataka under favourable environmental conditions. In the hill regions of Tamil Nadu, Diadegma semiclausiim Hellen exercises 70 per cent parasitization of diamondback moth in winter months.
Damage:
Caterpillars damage the leaves of cauliflower, cabbage and rape-seed (Brassica napus), particularly in the heart of the first two. Central leaves of cabbage or cauliflower may be riddled and the vegetables rendered unfit for human consumption. The pest is most serious when it appears on the early crop in August-September.
Control:
(i) Remove and destroy all the remnants, stubble, debris, etc. after the harvest of the crop and plough the fields.
(ii) Tomato, when intercropped with cabbage, inhibits or reduces egg laying by diamond-back moth.
(iii) Indian mustard, which attracts 80-90 per cent diamondback moths for colonisation, can be used as a trap crop.
(iv) Spray 750 ml of Dipel 8L or 750 g of Halt WP (Bacillus thuringiensis var. kurstaki) in 200-250 litres of water in the evenings at one week interval.
(v) Spray 625 ml of spinosad 2.5SC or 175 g emamectin benzoate 0.58G or 325 ml indoxacarb 15.8EC or 500 g cartap hydrochloride 50SP or quinalphos 35EC or 250 ml of fenvalerate 20EC in 250 litres of water per ha. Repeat sprays after 10 days, if necessary.
3. Cabbage Semilooper, Thysanoplusia Orichalcea (Fabricius) and Autographa Nigrisigna (Walker) (Lepidoptera: Noccuidae):
These two species are widely distributed in north-western India and are minor pests of cabbage, cauliflower and other winter vegetables. They are polyphagous and attack a number of plants, including groundnut and sunflower. The caterpillars are plump and palish green. They cause damage by biting round holes into cabbage leaves. On walking, they form characteristic half-loops and are often seen mixed with cabbage caterpillars.
The adults of T.orichalcea are light palish brown with a large golden patch on each fore wing. They measure about 42 mm across the spread wings. The adults of A. nigrisigna are darker and have dark-brown and dirty-white patches on the fore wings.
Life-Cycle:
These insects are active during the winter and it is not known how they survive the heat of summer. During the active period, they lay eggs on leaves of host plants and the caterpillars feed individually, biting holes of varying size according to the stage of their development. When full-grown, they pupate in the debris lying on the ground. The moths are very active at dusk on flowers in gardens and public parks, where they are seen in hundreds during the spring season.
4. Tobacco Caterpillar, Spodoptera Litura (Fabricius) (Lepidoptera: Noctuidae):
The tobacco caterpillar is found throughout the tropical and sub-tropical parts of the world. It is widespread in India and besides tobacco (Nicotiana tabacum L.), feeds on castor (Ricinus communis L.), groundnut (Arachis hypogaea L.), tomato, sunflower, cabbage and various other cruciferous crops.
The damage is done only by the caterpillars, which measure 35-40 mm in length at maturity. They are velvety black with yellowish-green dorsal stripes and lateral white bands. The moths are about 22 mm long and measure 40 mm across the spread wings. The fore wings have beautiful golden and greyish brown patterns.
Life-Cycle:
This pest breeds throughout the year, although its development is considerably retarded during winter. The moths are active at night when they mate and the female lays about 300 eggs in clusters. These clusters are covered over by brown hair and they hatch in about 3-5 days. The larvae feed gregariously for the first few days and then disperse to feed individually.
They pass through 6 stages and are full-fed in 15-30 days. The full-grown larvae enter the soil where they pupate. The pupal stage lasts 7-15 days and the moths, on emergence, live for 7-10 days. The life cycle is completed in 32-60 days and the pest completes eight generations in a year.
The natural enemies, Compoletis sp., Eriborus sp., Rogas sp. (Braconidae) and Strobliomyia orbata W. (Anthomyiidae) are associated with larvae of this pest.
Damage:
The larvae feed on leaves and fresh growth. They are mostly active at night and cause extensive damage, particularly in tobacco nurseries.
Control:
(i) Remove the egg masses and clusters of larvae and destroy them.
(ii) Chemical sprays recommended against diamondback moth will also work against this pest, but in this case spot application may be enough if the attack is not widespread in the field.
5. Crucifer Leaf Webber, Crocidolomia Binotalis Zeller (Lepidoptera: Pyralidae):
It is a serious pest of cabbage, radish, mustard and other cruciferous plants in India, Myanmar and Sri Lanka. The larvae web the leaves together and feed on them from the lower surface, often completely skeletonising them. The larva is green with a red head and it has longitudinal red stripes on the body. It is 2 cm in length.
Life-Cycle:
The activity of the pest coincides with the cruciferous crops. The moth lays eggs on the underside of leaves in masses of 40-100 each. The eggs hatch in 5-15 days. In the early stages the larvae feed gregariously on the leaf parenchyma. As they grow, they spread out and start webbing the leaves and feeding on them.
The larval stage is completed in 24-27 days in the summer and about 50 days in winter. When full-grown, the larva descends to the ground and pupates in the soil after making an earthen cocoon. The adult moth emerges in 14-40 days and the life-cycle is completed in 43-82 days. More than one generation may be completed in the season.
The larvae are parasitized by Microbracon mellus Ram and Apanteles crocidolmiae Ahmed (Braconidae).
Damage:
The caterpillars cause considerable damage to the crops by webbing the leaves together and feeding on them. They also feed on flower buds and bore into the pods.
Control:
(i) Remove and destroy the webbed leaves with larvae within.
(ii) Spray 940 ml of Malathion 50 EC or 320 ml of dichlorvos 100 EC in 250-300 litres of water per ha.
6. Cabbage Borer, Hellula Undalis (Fabricius) (Lepidoptera: Pyralidae):
The cabbage borer is one of the serious pests of cruciferous crops, having a worldwide occurrence. The larvae attack cabbage, cauliflower, radish, knol-khol, beet-root and the weed, Gynadropsis pentaphylla (Capparidaceae).
The damage is caused by the caterpillar which is 12-25 mm long and creamy yellow with a pinkish tinge and has seven purplish brown longitudinal stripes. The adult moth is slender, pale yellowish-brown, having grey wavy lines on the fore wings. Its hind wings are pale dusky.
Life-Cycle:
This pest breeds throughout the year but comes to the notice in autumn when the cruciferous vegetables are sown. The female moths lay eggs singly but more often in clusters, on the under surface of the leaves or some other parts of the plant. The colour of the egg is pinkish and their shape is oval.
The eggs hatch in 2-3 days. The caterpillars feed in the heart of the cabbage and become full-grown in 7-12 days, after undergoing four moultings. The full-grown caterpillar spins a cocoon among the leaves touching the ground or even inside larval burrows. The pupal period is about 6 days and the life cycle is completed in 15-25 days.
Damage:
The caterpillars first mine into the leaves. Later on, they feed on the leaf surface, sheltered within the silken passages. As they grow bigger they bore into the heads of cauliflower and cabbage. When the attack is heavy, the plants are riddled with worms and outwardly the heads look deformed.
Control:
(i) Collection and mechanical destruction of caterpillars in early stage of attack helps to check the infestation,
(ii) Since the attack is mostly in the nursery and on young plants in the field, spray 375 g of carbaryl 50WP in 150 litres of water per ha. Repeat spray at 10-day interval, pick all flowering heads before spraying and observe 7 days waiting period after spray for the next picking.
7. Cabbage Flea Beetles, Phyllotreta Cruciferae (Goeze), P. Chotanica Duvivier, P. Birmanica Harold, P. Oncera Maulik and P. Downesi Baly (Coleoptera: Chrysomelidae):
The cabbage flea beetles attack almost all the cruciferous plants in Europe, erstwhile USSR, North and South America, Australia, Japan and India. The common field crops like mustard, raya, taramira, toria and vegetables like radish, turnip, cabbage, cauliflower and knol-khol are severely damaged by adult beetles in West Bengal and Uttar Pradesh. Some winter flowering plants, namely dahlia, sweet sultan, antirrhinum and sweet peas also provide food for the beetles.
The dorsum of the adult beetle, P. cruciferae, is metallic blue in colour, with a greenish hue. The body is elongate narrow in front but broad distally. The beetle is round at the anal end. The head is finely punctate and the antennae extend beyond the middle of elytra. The female beetle measures 2.0 mm in length while the male beetle measures 1.8 mm. The larva is dirty white in colour with pale white head and measures about 5 mm in length.
Life-Cycle:
This pest is active throughout the year except during the winter months, when it hibernates in the soil or among plant debris. The over-wintered adult beetles emerge in the last week of February or in the beginning of March and settle on the growing cruciferous plants.
The female beetle lays 50-80 creamy white eggs singly in the soil around the host plants, during the oviposition period of 25-30 days. The incubation period ranges between 5-10 days. The larva is very active and feeds on the tender roots of the host plant. It moults thrice during a total larval period of 9-15 days.
The larva before entering into the pre-pupal stage wriggles out of the mined roots and prepares an earthern cell, 0-5 mm long, in the vicinity of the infested plants. There it pupates. The pre-pupal period is 2-4 days and the pupal stage lasts 8-14 days. There are 7-8 generations of this pest in a year.
The adults are parasitized by Microctonus indicus (Braconidae).
Damage:
The adults mostly feed on the leaves by making innumerable round holes in the host plants. The stem, the flowers and even pods may also be attacked. The old, eaten away leaves dry up, while the young leaves are rendered unfit for consumption. A special kind of decaying odour is emitted by the cabbage plants attacked by this pest.
Control:
Spray 2.5 kg of carbaryl 50WP in 250 litres of water per ha.