Learn about the pests that damage cotton and its control.
1. Cotton Semilooper, Tarache Notabilis (Walker) (Lepidoptera: Noctuidae):
This insect is found throughout the plains of Pakistan and India as a minor pest of cotton, but in certain years, it assumes a serious form. Besides cotton, it also feeds on the leaves of sonchal (Malva parviflora), brinjal, etc.
The full-grown caterpillars are about 40 mm long and dark green, having six pairs of black and bright- yellow spots on the back. As they move, they bend the body, forming half loops and hence the name semi- looper. The adults are stoutly built, white moths, with prominent grey and brown spots on the wings, measuring 30-32 mm across.
Life-Cycle:
The pest is active from April to October and passes the winter as an hibernating pupa. The moths appear in March-April and are active at night. They lay green, rounded eggs singly, on the underside of leaves. The eggs hatch in 2-4 days and the caterpillars immediately start feeding voraciously.
They are full-fed in 9-16 days and then descend to the ground, where they construct earthen cells at a depth of 3 cm for pupation. They emerge as moths in 5-14 days and are short-lived. The life-cycle is completed in 16-34 days. By October-November, they complete 4-5 generations.
The parasitoids associated with larvae of this pest are Actia monticola Mall, and Exorista seviloides Bar. (Tachinidae).
Damage:
The caterpillars feed on cotton leaves and skeletonize them altogether. In years of heavy infestation, the plants may be completely denuded of leaves.
Prevention and Control:
(i) The incidence of pest on the next crop can be minimized by ploughing the fields soon after cotton harvest or by growing clovers in rotation with this crop.
(ii) Chemical control measures are same as in case of pink bollworm.
2. Green Semilooper, Anomis Flava (Fabricius) (Lepidoptera: Noctuidae):
The green semi-looper which feeds on leaves is widely distributed throughout the cotton growing areas of Africa, Asia and Australia. In India, it is a sporadic pest of cotton and sometimes causes a serious damage to the crop particularly in Gujarat and Rajasthan.
Besides cotton, the larvae also feed on Hibiscus esculentus L., Hibiscus cannabinus L., and Phaseolus radiatus L. among the cultivated plants and on Hibiscus rosasinensis L., Sida cardifolia L., Althaea rosea CAV., Bombyx malabaricum DC. and Malachra capitata L. among the forest trees.
The full-grown larva is 25-30 mm long and is pale- yellowish green with five white lines arranged longitudinally on the dorsal surface. The adult is an attractive, small moth with reddish-brown fore wings traversed by two darker zig-zag bands. The hind wings are pale brown.
Life-Cycle:
The emergence of moths coincides with the warming up of the season. The female lays up to 600 eggs on leaves during an opposition period of 8-12 days. The eggs hatch in 4-5 days. The larvae which move around with a characteristic semi-loop crawl and feed on leaves. They complete development by passing through 5 instars within a period of 18-20 days.
They make a loose cocoon before pupation, either within the leaf folds or among debris in the soil. The pupal period lasts 8-9 days. The moths have a life-span of 12-13 days and the life-cycle is completed in 4-6 weeks. More than one generation is completed in a crop season.
Damage:
The young larvae congregate in small groups and move actively and feed on leaf lamina making small punctures. The grown-up larvae feed voraciously on the entire leaves, leaving only the main veins. The caterpillars also eat the tender shoots, buds and bolls. Sometimes, the attack is heavy and the plants may be completely defoliated.
3. Bud Moth, Phycita Infusella (Meyrick) (Lepidoptera: Pyralidae):
This insect is found throughout India as a minor pest of cotton and is more serious on desi than on the American varieties. It is sporadic in occurrence and becomes serious in certain localities only. Apart from cotton, it also feeds on okra and other allied plants. In the caterpillar stage, it makes characteristic webbings around the terminal young growth of leaves, where it feeds.
The full-grown greenish caterpillars are 13-16 mm long, having a black front and faint brown stripes on the rest of the body. The adult is a greyish-yellow moth, speckled with fuscous, and measures 20 mm across the wing expanse. The front wings are faint yellow at the base with red wavy lines and the hind wings are white, with brown marginal lines.
Life-Cycle:
The pest is active from April to October and passes winter as a hibernating caterpillar in debris on the ground. The moths appear in April and lay small rounded eggs on tender leaves of cotton or other host plants. The eggs hatch in about 7 days and the young larvae start feeding on bud or young leaves.
As the larvae grow, they web together the terminal leaves with silken threads and feed inside. They are full-fed in 21 days and make silken cocoons in the midst of twisted leaves. The pupal stage lasts 11 days and the moths, on emergence, live for a few days only. The life-cycle is completed in 5-6 weeks and the pest completes 4-5 generations in a year.
Bracon brevicornis Wesmael and B. kitcheneri Will. (Braconidae) are associated with larvae of this pest.
Damage:
Due to the webbing of leaves and feeding by the caterpillars, further growth of the plants is inhibited. The attacked leaves wither away, dry up and drop off. The flowering and fruiting are very poor and the reduction in yield is considerable.
Prevention and Control:
Spray 2.0 kg of carbaryl 50WP in 315-375 litres of water per ha.
4. Tobacco Caterpillar, Spodoptera Litura (Fabricius) (Lepidoptera: Noctuidae):
Tobacco caterpillar is a polyphagous pest and the larvae cause serious damage to cotton from August to November. The young larvae feed gregariously and skeletonize the foliage. The grown up larvae disperse and feed singly. Besides leaves, they also damage the buds, flowers and green bolls.
Prevention and Control:
(i) Avoid growing castor, moong, dhaincha (Sesbania aculeata) and okra in and around cotton as these are the most preferred hosts of tobacco caterpillar and help the pest to multiply before shifting to cotton,
(ii) Plough the dhaincha crop immediately when it has attained reasonable height and bury the larvae along with the straw deep into the soil,
(iii) Keep the fields free from the weed (Trianthema portulacastrum), as it acts as an alternate host of the insect.
(iv) Collect and destroy the egg masses and young larvae feeding gregariously on the cotton crop,
(v) Spray 2-0 kg of acephate 75SP or 5-0 litres of chlorpyriphos 20EC or 2-0 litres of quinalphos 25EC or 625 g of thiodicarb 75WP or 375 ml of novaluron 10EC or 750 ml of pyridalyl 10EC or 150 ml of chlorantraniliprole 18.5SL in 250 litres of water per ha.
5. Cotton Grey Weevil, Myllocerus Undecimpustulatus Faust (Coleoptera: Curculioniaae):
This insect is found throughout India and is a minor pest of cotton, particularly of the desi cotton varieties. It also feeds on a number of other cultivated plants such as bajra (Pennisetum typhoides), maize, sorghum, guava, arhar (Cajanus cajan), groundnut, etc. The plants are attacked by the weevils which are prominent above the ground as well as the grubs which feed on the underground parts. The weevils are grey and are 3-6 mm long. The grubs are white, legless, and cylindrical are about 8 mm in length.
Life-Cycle:
The pest is active from April to November and passes winter in the adult stage hidden in debris. The weevils appear in April-May and lay ovoid, light yellow eggs in the soil. A female lays, on an average, 360 eggs over a period of 24 days. The eggs hatch in 3- 5 days in May-September and the young grubs feed on the roots of cotton and other plants.
The grubs complete their development in 1-2 months. They pupate in the soil inside earthen cells, forming creamy-white pupae, which change into adults in about one week. The adults live for 8- 11 days in the summer and 4-5 months in the winter. During the active period, the life-cycle is completed in 6-8 weeks and the pest probably breeds 3-4 times in a year.
Dinocampus mylloceri Walker (Braconidae) parasitizes the larvae of this insect.
Damage:
Both adults and grubs cause damage. The grubs feed underground on the roots of cotton seedlings and destroy them. One grub can destroy 9 seedlings in 40 days. The adults which feed on leaves, buds, flowers and young bolls cut prominent round holes.
Prevention and Control:
(i) The pest can be suppressed by disturbing the soil up to a depth of 7.5 cm and destroying the eggs, grubs and pupae,
(ii) Spray 2.5 kg of carbaryl 50 WP in 375 litres of water per ha.
6. Cotton Stem Weevil, Pempherulus Affinis (Faust) (Coleoptera: Curculionidae):
The grubs of cotton stem weevil feed on many species of cotton in India, Myanmar, Thailand and the Philippines. In India, it occurs in Tamil Nadu, Andhra Pradesh, Karnataka, Kerala, Bihar, Orissa, Rajasthan, Uttar Pradesh, Gujarat and Assam. The most favoured host of this insect is Triumfetta rhomboidea Jacq.
The grubs feed on the soft tissues of cotton stems. Greyish-black weevils emerge from the stem killing the plants. The adult is a dirty brown or greyish-black weevil, about 3 cm in length. The grub is slightly curved, creamy white, with a distinct head.
Life-Cycle:
The weevils emerge from the cotton sticks wherein they spend the summer. After mating, the female makes a cavity in the hypocotyle region of the plant and lays an oval, globular, smooth, milky white egg. During an opposition period of 60-80 days, a female may lay up to 121 eggs visiting from plant to plant.
The eggs hatch in 6-10 days and the grubs feed inside the soft stem tissue. They continue to feed inside till the development is completed in 35-57 days. The pupation takes place inside the stem and this stage lasts from 25 to 30 days. Three generations are completed in a year from October to April and the summer is passed as an adult in the cotton sticks.
Damage:
The pest causes serious damage to Cambodia cotton in South India. As the grubs tunnel within the stem, that portion swells, and such symptoms are generally seen at the base of the plant. The younger plants when attacked succumb, while the older plants may survive but suffer in vigour. Under strong winds, the affected plants may break at the swellings. The pest causes plant mortality upto 25 per cent, especially during the early stages of growth.
Prevention and Control:
(i) Collection and destruction of affected plants is recommended for the control of this pest, and
(ii) Avoid growing of alternate or collateral host plants during the off season.