Everything you need to know about cotton cultivation. Learn about:- 1. Description of Cotton 2. Habitat of Cotton 3. Climate Suitable 4. Soil Suitable 5. Cultural Operations 6. Harvest and Yield 7. Diseases 8. Pests.
Contents:
- Description of Cotton
- Habitat of Cotton
- Climate Suitable for Cotton Cultivation
- Soil Suitable for Cotton Cultivation
- Cultural Operations for Growing Cotton
- Harvest and Yield of Cotton
- Diseases of Cotton
- Pests of Cotton
1. Description of Cotton:
A small shrub or large herb, erect, reaching 9 or 10 feet in height, with many widely spreading branches; stem stiff, cylindrical, solid, smooth or pubescent, somewhat striate, purplish or green, sprinkled with numerous small, raised, black, dot-like glands.
Leaves alternate, numerous, spreading, on stiff round petioles about or nearly equalling the blade, and covered with similar black dots to those on the stem; stipules rather large, linear-lanceolate, the upper ones falcate, usually soon deciduous; blade 3—6 inches long, and about as wide, cordate at the base, palmately cut about half way or more down into 3 or 5 acuminate entire lobes, or the lower ones ovate, entire, usually covered with deciduous stellate down when young, when mature glabrous on both surfaces, bright green above, paler beneath and with 3 prominent veins, on the centre one of which near its base is a prominent oblong gland.
Flowers large, 3—4 inches in diameter, on stout, spreading, stiff angular pedicels opposite the leaves (really terminal), somewhat thickened upwards and sprinkled with prominent black glands; epicalyx of three very large bracts about 2 inches long, chordate and entire at the base, deeply laciniate with numerous large attenuated somewhat falcate teeth, glabrous, green, ribbed with veins, dotted with glands. Calyx small, about ½ inch long, entirely concealed by the bracts, tubular- campanulate, truncate or faintly’ 5-lobed at the margin, glabrous, parallel-veined and gland-dotted.
Petals 5, strongly convolute in aestivation, spreading but much overlapping, slightly connected to form a very short tube at the base, longer than the bracts, 2½ —3 inches, irregularly obovate-truncate, wedge-shaped at the base, very unequal-sided, pilose externally, finely veined and sprinkled with minute black dots, bright sulphur yellow with a crimson blotch near the base, or pale vinous red.
Stamens numerous, united to form, a long tube, which is fused with the base of the petals below, and is covered with small round or reniform 1-celled yellow anthers on slender filaments. Ovary conical, smooth, dotted, 3 to 5 celled, with numerous ovules; style simple, passing through the staminal tube and projecting beyond its mouth; stigma clavate, slightly 3—5 lobed. Fruit an ovate-ovoid acute or acuminate capsule, 1½ —2 inches long, surrounded and inclosed by the persistent bracts of the epicalyx, smooth, dark brown, loculicidally dehiscent into 3—5 valves.
Seeds numerous, closely packed, but usually easily separable from one another, irregularly ovoid; testa dark brown, rather thick, hard, entirely covered with very numerous long, very delicate, simple, pure white, flexuous hairs about 1 inch long, which are readily removed from the testa and leave a smooth bare surface; embryo completely filling the seed, dotted with small black sunk glands; radicle short, clavate, cotyledons large, much doubled and folded; no endosperm.
2. Habitat of Cotton:
It is probable that this species of cotton is, as its name indicates, a native of the West Indies; this cannot, however, be stated with complete certainty. Its culture is now spread over a large part of the warmer regions of the globe, and under one or other of its forms it is very largely grown in the West Indies, the Southern United States, Central and S. America, tropical and North Africa, the hot parts of Australia, and even the south of Spain.
It affords the best long staple cottons of commerce; Sea Island, Kidney, Peruvian, Brazil, Bahia, &c., being the produce of different varieties. It is the clean separation of the long hairs from the seed which especially gives this species its value, but this character appears not to hold good in all its varieties.
The plant has become naturalised in Western Tropical Africa, and then becomes much more hairy; but Dr. Welwitsch was convinced it was nowhere truly wild there, the only native species being the very distinct G. anomalum, W. & P., which also occurs in Nubia.
Cotton is afforded by the other species o the genus, of which by far the most important is G. herbaccum, Linn. This differs from G. barbadense in its smaller size, less dividede leaves and bracts, smaller petals and fewer seeds from which the cotton hairs do not readily separate and which have a short downy covering on the testa.
3. Climate Suitable for Cotton Cultivation:
For successful cultivation, cotton crop requires a frost-free growing season of c. 200 days, a hot summer, sufficient soil moisture and a fairly dry harvesting season. The plant does not tolerate heavy rainfall and cannot be grown at high altitudes. Its cultivation is confined to flat or undulating tracts, up to 3,000 ft. above sea level. Of the various climatic factors which influence growth, yield and quality of cotton in India, rainfall and temperature are important.
It is stated that rainfall alone accounts for about 1/3 to ½ the total amount of annual variation in quality. It is not the average rainfall that determines the yield or quality of the crop, but its distribution in a specified period of crop development. Adequate, but not excessive moisture is required in the early stages of growth; a relatively drier period during flowering and no rainfall during ripening or picking.
The cotton plant can be grown only in areas which are nearly tropical, with a temperature not below 70°F.; it can stand temperatures upto 110°F. The productivity of the plant is heightened if the developmental and maturing periods coincide with periods of high temperature. It has been found in Madras that Cambodia cotton sown in the summer season yields more cotton (of better lint quality) per acre, than when sown as a winter crop.
Similarly in Punjab, where the growing season is limited by the onset of cold weather verging on frost the yield per acre can be appreciably increased by shifting the sowing period to an earlier date, particularly where irrigation facilities are available and where there is no fear of incidence of tirak.
4. Soil Suitable for Cotton Cultivation:
The cotton-growing areas in India can be divided into three main tracts according to soil types, viz. the Indo-Gangetic alluvium, the black cotton (regur) soil of Peninsular India and the red soils of southern India. The soils of the Indo-Gangetic alluvium are clayey or sandy and cotton is cultivated mostly as an irrigated crop, except in small areas in Punjab, U.P. and Bihar, where it is grown under rain-fed conditions.
In the black cotton soil tract, which comprises the bulk of the cotton area in India, the soil is deep, heavy and black, rather clayey, cracking badly when dry, but not disintegrating completely, and swelling and loosening up after the rains; the soil contains appreciable amounts of calcium, but is low in organic matter; it is fertile and retentive of moisture. In this tract, cotton is grown mostly under rain-fed conditions.
The red soils of S. India are light, porous and friable; they contain high percentages of iron and alumina, but the percentage of calcium is low. These soils are usually preferred for the cultivation of American cottons under irrigation.
The bulk of the cotton crop, c. 93%, is grown under rain-fed conditions in India. The rainfall of the cotton tracts ranges from 10- 12 inches in parts of the Punjab, Rajasthan, Kutch, Saurashtra and Gujarat, 25-30 inches in Central India and the Deccan, 50 inches in parts of Bihar, Orissa and Bombay and over 100 inches in the hills of Assam. In areas having a rainfall upto 25 inches occasional irrigation greatly benefits the crop. Only a small part is cultivated under irrigation particularly in parts of Madras, Punjab, P.E.P.S.U., Rajasthan and UP.
5. Cultural Operations for Growing Cotton:
Cultural practices vary in different parts of India owing to differences in soil and climate. In the dry black cotton soil tracts of Peninsular India, the land is ploughed generally once in 3-4 years. Preparation of land consists merely in harrowing 2 or 3 times with a blade harrow, the main consideration being conservation of moisture rather than turning over the soil.
Experimental trials in the rain-fed tracts have shown that apart from the suppression of weeds, deep cultivation has no perceptible effect on the yield of cotton; in some cases, deep cultivation is reported to have affected the yield adversely. In the case of irrigated cottons in Madras, Mysore, U.P. and Punjab, however, the land is thoroughly ploughed, but even here, more than four ploughings are seldom given.
The implements used in cotton culture are primitive. In the black cotton soil tracts, wooden ploughs and blade harrows are the chief implements used for preparing the soil and wooden seed drills for sowing in lines. Large wooden ploughs and iron mould board ploughs are used in tracts infested with weeds.
As the period and intensity of rainfall vary considerably in different parts of the country, the sowing and harvesting seasons are spread over many months of the year.
Cotton is propagated mostly by seed. It can be propagated vegetatively by cuttings. Vegetative propagation is particularly useful in acclimatising exotic types, like Egyptian and Sea Island cottons, or for propagating selected hybrids grown by budding or grafting. Cuttings taken from any part of the plant take root, but those from the main axis with a girth of 1 cm. or more are preferred. Cuttings treated with hormones, e.g. Seradix B, give a higher percentage of rooting than untreated ones.
The seeds pass through a period of dormancy before germination. Germination is not satisfactory if sown within 2 or 3 months after the opening of bolls. Normally, cotton seeds are not stored for more than 5 or 6 months. Dry seeds stored under proper conditions retain viability for at least 2 years. Recent studies in America have shown that seeds containing not more than 7% moisture and stored at 90°F retain their viability for as many as 15 years.
It has long been recognised that sowing of good seeds is essential for getting optimum yields of crops. Seeds which are of high density and of large size give a high percentage of germination and seedling growth is vigorous; the initial vigour persists during later growth resulting in an increased yield of cotton. The response of seed selection in desi varieties is more pronounced than that in American cottons. Seeds can be selected for size by sieving and for density by gravity separation, by suspending in a salt solution of the desired density.
Seeds are usually sown broadcast or in lines by drills. The distance between rows varies from 12 to 36 in. according to the type of cotton, the fertility of the soil and, if grown as a mixed crop, the type of crop with which it is grown. In general, American cottons grown under irrigation are given wider spacing. When cotton is grown pure, a spacing of 18 in. between rows and 12 in. between plants ensures a full field population, without leaving unnecessary gaps.
Seeds are usually pre-treated with mud or cow dung to render sowing by drills easy. Delinting and treatment with chemicals, like sulphuric acid or zinc chloride, are also recommended. Soaking in water for 12-24 hours also facilitates germination. It is stated that coating of seeds with ammonium sulphate not only hastens maturity of the crop but also improves yield. In Russia, vernalisation or iarovization of seeds has been tried to hasten maturation and improve crop yield.
The seed rate varies from 5 to 20 lb. per acre depending upon the fertility of the soil, the type of cotton and whether the crop is grown mixed or pure. For desi cotton, the seed rate is c. 10 lb. per acre when sown pure and 7 lb. per acre when sown as a mixed crop. The seed rate for American cottons, particularly fuzzy-seeded Punjab American types, is higher.
American cottons are generally grown pure, while desi cottons are grown in mixture. Some 22 crops suitable for cultivation in mixture with cotton have been listed, the more important among them being Sorghum vulgare and Setaria italica. Inter-cropping with groundnut has been recommended for raising cotton yield. Desi and American cottons are sometimes grown together in parts of Punjab and two types of desi cottons are grown together in parts of Madhya Bharat and Madras.
While this is considered harmful from the point of view of purity of the crop, it has been shown that in areas in which the soil is heterogeneous and weather hazards are high, the growing of cottons in mixture has definite advantages. However, where two pure strains of the same species, possessing more or less identical characteristics are grown in mixture, there is a possibility of natural crossing and consequent risk of deterioration in quality.
Cotton cultivation is generally preceded or followed by an appropriate rotation crop. In the Punjab, P.E.P.S.U., U.P, and Bihar the most commonly practised rotations are – Cotton — wheat, cotton — jowar and cotton — wheat — toria. In the black cotton soil tracts of Peninsular India, jowar usually precedes cotton. It has been stated that growing of jowar raises the sodium ion concentration in the soil and the yield of the following cotton crop thereby suffers. The ill effect of jowar cultivation can be corrected by growing a leguminous crop, e.g., groundnut, sunn-hemp, guar or indigo.
After cultivation, operations consist of inter-culturing between rows or hand weeding wherever climatic conditions permit. Black cotton soils are mostly free from weeds of cultivation. In some places, plants are thinned when 1-1 ½ months old to 9-12 in. apart in rows and off-type plants, if any, are rogued. American cottons are sometimes topped when c. 3 ft. high in order to induce branching.
Practically no manure is given to the crop when grown under rain-fed conditions. The field is sometimes lightly manured by penning sheep or by adding farmyard manure or oil cake. Usually, it is the crop preceding the cotton that is manured. Studies carried out in various centres in India show that both irrigated and rain-fed cottons respond favourably to nitrogenous fertilizers and organic manures, provided the soil is not saline and the rainfall is adequate.
Manuring is profitable only on soils of medium or high fertility and the rate of increase in yield per unit quantity of nitrogen increases with increasing fertility. Application of potash and phosphatic fertilizers is reported to increase the oil content of cotton seeds, while the application of nitrogen decreases the oil percentage and increases the protein content.
In the case of irrigated cottons, the frequency of irrigation varies with the amount of rainfall and the water holding capacity of the soil. In Punjab, irrigation at the time of blossoming has been found advantageous. In Madras, where Cambodia cotton is grown under irrigation, the summer crop yields cotton of better quality than the winter crop.
In the case of the latter, irrigation is necessary once a fortnight in the early stages and more frequently during the period of boll formation. The optimum spacings are ft. between rows and 9 in. between plants in the row. Planting on sides of ridges, as in Egypt, ensures a more uniform crop than planting in beds and also a definite saving in irrigation water.
The first blossoms appear in 7-10 weeks after planting. Generally, the opening of flowers follows a spiral course, commencing with the lowest and ending with the topmost flowering branch. The flowers remain open only for a day. They are pollinated shortly after opening. Until recently self-pollination was presumed to be the rule; it is now known that a certain amount of cross pollination takes place by the agency of insects, particularly bees.
The amount of cross fertilization appears to differ in different types and depends upon such factors as relative rate of blossoming, the distance between plants, and the relative abundance of insect pollinators.
The development of bolls begins immediately after fertilization and is fairly rapid. The full size of the boll is reached in about 4 weeks after fertilization. It has been observed that all flowers in a maturing crop do not produce bolls and all bolls do not yield cotton. Since the yield of cotton is directly dependent on the number of mature bolls, shedding of immature bolls is a matter of great concern to cultivators.
Shedding may take place at any period in the development of the boll and is mainly due to physiological causes. It is also brought about by pests and diseases. Broach cotton have shown that bud and boll shedding is brought about by insufficient nutrition and may be minimised by the application of nitrogenous fertilizers at all stages of crop development.
6. Harvest and Yield of Cotton Crop:
The cotton crop is usually harvested in 3 or 4 pickings, taken at suitable intervals. Picking is carried out by hand, mostly by women, the amount of cotton collected ranging from 20 to 60 lb. per day per person; in the case of irrigated Cambodia cotton, the quantity picked may be as high as 100 lb. per day. The quantity picked depends not merely on the skill and energy of the picker, but on the abundance of open bolls, the size of bolls and the picking quality of the cotton harvested. Quick picking is facilitated by growing types in which bolls mature uniformly and open widely.
Cotton should be picked only when the bolls are fully mature, fully open and the floss has puffed up consequent on exposure to sun. Harvesting from half-open or immature bolls yields cotton containing large percentages of immature fibres and trash. Further, owing to the dry weather prevailing during the picking season in most cotton areas, picked cotton often contains dried bits of leaves and bracts.
Clean picking is necessary as the market value of cotton is adversely affected by the presence of immature fibres and extraneous material. In areas subject to bollworm attack, damaged or stained cotton, which lowers the market value of the produce, should be eliminated before ginning.
The average yield of cotton varies in different tracts even within the same State, depending upon the type of cotton grown and the cultural practices; it also varies from year to year depending upon the vagaries of the monsoon. The average yield in terms of ginned cotton per acre ranges from 50 lb. in Hyderabad to 260 lb. in P.E.P.S.U. These figures represent yields under widely differing conditions, the former under rain-fed conditions and the latter under irrigation.
The yield per acre is low in India as compared to yields in other countries. The yield has remained practically stationary, except for small increases brought about by the introduction of improved varieties. It is a well-known fact that a cotton type, even with a hereditary background for high yield, gives its best performance only when it is sown at the proper time and grown under favourable conditions of soil, climate, optimum spacing, manuring and cultivation.
The low average yield in India is attributed to low fertility of soils, and to the circumstance that nearly 90% of the area is dependent on rainfall. Further, weather hazards are high since the cotton-growing areas in India are widely scattered over many latitudes. Improvements in yield due to the introduction of improved strains are often counter-balanced by adverse seasonal conditions and consequently, the spread of high-yielding strains, though fairly extensive, has failed to produce a perceptible change in the average acre yield.
Under the Grow More Cotton Scheme, intense efforts are being made for raising the acre yield by distributing improved seeds, application of manures like ammonium sulphate, extension of irrigation facilities and adoption of improved cultural practices including prophylactic measures against pests and diseases.
7. Diseases of Cotton:
The more serious diseases of cotton in India are wilt and root rot. Anthracnose occasionally causes damage, particularly in years of heavy and continuous rainfall. Of the physiological disorders, red leaf blight and tirak (bad opening of bolls) are serious. Small leaf or stenosis is caused by a virus. Other diseases of cotton are of minor importance, occurs sporadically or are confined to certain tracts or affect certain types of cotton.
Wilt caused by Fusarium vasinfectum Atk. is widely prevalent in the black cotton soil areas of Deccan and Gujarat; it is practically absent in the Indo-Gangetic plain. The main symptom of the disease is drooping or wilting of leaves which starts from the old leaves at the base and gradually proceeds upwards, finally involving the entire branch or the whole plant.
Affected leaves turn yellow or brown and are shed. The disease may affect plants at any stage of growth; its incidence is particularly high in plants which have completed vegetative growth.
Various species of Gossypium are attacked, but types belonging to G. hirsutum and G. barbadense are immune from the Indian strain of the fungus. As the fungus persists for several years in the soil, crop rotation is of little value as a control measure. The development of wilt-resistant strains is the only means of fighting the disease and such types have been evolved to suit various tracts.
Some of the wilt-resistant strains under general cultivation are Jayawant and Jayadhar in Karnatak, Jarila and Virnar in Khandesh, Vijay in Gujarat, Strain 2087 in Surat, Kalyan in Saurashtra, H-420 in Madhya Pradesh, Gao-rani-12 in Hyderabad and Bhoj in Madhya Bharat.
Root rot is caused by Macrophomina phaseoli (Maubl.) Ashby; this organism and Corticium solani Bourdet & Galzin are both involved in the causation of the disease in Punjab. The disease is widely distributed in Punjab and is particularly severe in irrigated tracts. It is also common in the sandy alluvial soils of north Gujarat and, to a less extent, in the black cotton soil areas of western and southern India.
The most striking symptom of the disease is the sudden and complete wilting of affected plants; almost all branch roots decay and the entire plant can be easily pulled out of the ground with the tap-root intact. American and Asian types of cotton are susceptible, but G. arboreum race indicum (Rozi cotton) is reported to show a high degree of field resistance. M. phaseoli has a wide range of hosts and attacks a variety of crops.
It has been found in Punjab that early and late sowing (in the first week of April or end of June) contribute to a marked reduction of root rot in indigenous and American cotton types since, the resultant stands escape the period of maximum virulence of the causal organism. Inter-cropping of cotton with jowar or moth (Phaseolus aconitifolius Jacq.) also reduces disease incidence, as shading of ground checks rise in soil temperature. Cultivation of resistant types will provide the ideal means of control, but such types have not been evolved so far.
Anthracnose is caused by Colletotrichum indicum Dastur and is common in Madras. It has been reported from Madhya Pradesh, Bombay and Bengal. The damage due to this disease is, however, insignificant. The fungus causes damping off of seedlings. When the bolls are attacked, the damage is serious; the bolls dry up or are shed before maturity.
Bolls of all sizes are attacked and lint hairs in contact with the diseased portions are stained yellow or brown, or are clumped into a solid, brittle mass of fibres. Types of cotton belonging to G. herbaceum and G. arboreum race bengalense and race indicum are attacked, although the latter shows greater resistance to the disease. The fungus occurs also on common weeds like Aristolochia bracteata Retz. and Hibiscus sp.
As the disease is transmitted by seed, the use of clean seeds for sowing provides a method of control. Good results are obtained by immersing the seeds for one hour in 0.25% Uspulun (hydroxymercuri-chlorophenol), dusting with the same preparation, or delinting with sulphuric acid (1 part of acid to 15-20 parts of seeds by volume). Two applications of Bordeaux mixture to seedlings and use of wider spacing in sowing have proved effective in controlling seedling blight and also in checking boll rot. Removal of collateral hosts aids in controlling seedling blight.
Small leaf (Stenosis or Smalling) is a virus disease prevalent in Bombay, Madras and Punjab. In Bombay, G. herbaceum and the perennial cotton Rozi (G. arboreum race indicum) are the worst affected; in Madras, Mungari cotton shows high susceptibility; in Punjab, the attack is confined mostly to American types, though a few indigenous types are also susceptible.
Small leaf is characterised by diminution in the size of all plant organs. The leaves get crinkled and deformed, and a distinctive mosaic appearance is imparted by the appearance of reddish or pinkish yellow patches. The number of leaf lobes is reduced. The root system is poorly developed and affected plants can be pulled out easily with the tap-root intact. Affected plants are often sterile.
The Incidence of small leaf is correlated with abnormal weather conditions. The disease can be transmitted by grafting, but not by sap or seed. No insect vector has been discovered so far.
Red leaf blight is a physiological deficiency rather than a disease, occurring in all areas where American cottons are cultivated. Glabrous types are more susceptible than hairy ones. Asian cottons are on the whole immune. Three kinds of red leaf may be distinguished and any one, any two, or all the three together, can be present in a G. hirsutum crop. Natural or genetic red leaf makes its appearance only when the plant is in the active reproductive phase.
It does not harm the plant; in fact, it hastens maturity. The second type of red leaf is associated with jassid attack. Jassid-resistant cottons are free from this type of red leaf. The third type of red leaf is caused by nitrogen deficiency in the soil or by water-logging. Application of ammonium sulphate at the proper time provides control.
Tirak or bad opening of cotton bolls is another physiological disorder affecting American cottons in Punjab. The extent and severity of the disorder vary from year to year. The first symptom is yellowing, drooping or shedding of leaves. The bolls remain small, crack prematurely and seeds, which remain immature, bear lint of poor quality. Two sets of soil conditions are associated with the development of tirak, viz., soils which are deficient in water and containing alkali salts in the subsoil from the second or third foot downwards and soils deficient in nutrients, especially nitrogen.
The application of sulphate of ammonia proved beneficial in reducing tirak in crops cultivated on light sandy soils deficient in nitrogen; it is ineffective in the case of crops grown on sandy loams with saline subsoil. In the latter case, the incidence of tirak may be minimised by late sowing in June and heavy irrigation’ at short intervals, beginning with mid-August.
Late sowing reduces vegetative growth and prevents water deficiency in the crop, while, heavy and more frequent irrigation ensures enough water supply from the upper non-saline layers of the soil. It has been observed that late sowing contributes to tirak reduction even in soils deficient in nitrogen. However, it adversely affects the number of bolls per plant, but this disadvantage can be remedied by thicker sowing.
Diseases of minor importance affecting cotton crops in India are dry rot or sore shin caused by Macrophomina phaseoli (Maubl.) Ashby; sclerotium wilt caused by Corticium rolfsii (Sacc.) Curzi; wet rot or damping off caused by Phytophthora parasitica Dastur and a species of Pythium; boll rot caused by Aspergillus niger van Tiegh.; internal boll disease caused by Nematospora nagpuri Dastur; brown speck (sooty mould) caused by Capnodium sp.; black arm or angular leaf spot caused by Xanthomonas malvacearum (E.F. Sm.) Dowson; cotton rust caused by Cerotelium desmium Arth.; grey mildew caused by Ramularia areola Atk.; and root knot caused by an eelworm.
Of these, the black arm disease is common in American cottons in Madras, Karnataka and Madhya Pradesh. The disease is caused by the bacterium which occurs in the soil or in cotton seeds. Though of minor importance, it causes heavy losses in some years. Selection of resistant strains is the only practical means of control.
Some strains of G. arboreum and G. herbaceum are immune to this disease. In Madras, Strain-2196 has been found resistant under varied conditions of season and soil. The use of fungicides is regarded only as a palliative, not a solution, for the control of black arm. Jatropha curcas Linn, is reported to serve as a collateral host for the bacterium.
8. Pests of Cotton:
Nearly 50 insect pests affecting cotton crops have been recorded in India. The more important among them are spotted bollworms, pink bollworm, jassids and stem weevil. In certain areas, a leaf roller and two types of bugs cause serious damage.
There are two types of spotted bollworms, Earias fabia Stoll, and E. insulana Boisd., almost similar in shape and form. E. insulana is a green moth with a spiny caterpillar shape and E. fabia is a partially green moth with a smooth-bodied caterpillar shape. The damage caused by both bollworms is similar. They attack growing shoots, buds, flowers and bolls. Their multiplication in the field is favoured by cloudy, drizzling weather.
Affected young plants are characterised by drooping and fading of top shoots; in mature plants, the buds, flowers and bolls are shed. Young worms attack tiny buds of growing shoots or bore into succulent internodes, 3-4 in. below the tops of shoots, and destroy flower buds as soon as they appear. Developing bolls are also attacked and are generally shed; those which remain attached do not open or even if they open, they contain practically no cotton.
The pest is kept under control by a number of parasites and predators. Damage due to spotted bollworms can be reduced by the destruction of affected shoots at the commencement of the growing season, by complete removal of standing cotton sticks from fields soon after the harvest, and by non-cultivation of malvaceous plants like bhindi (Hibiscus esculentus) in the same area during the period between two cotton growing seasons.
A small implement has been devised for removing standing cotton stalks from the field. Recent trials have shown that spraying with DDT reduces the severity of infestation.
Pink bollworm (Platyedra gossypiella Saund or Pectinophora gossypiella Saund) is a serious pest of cotton in many parts of India, particularly in Punjab, Uttar Pradesh and Hyderabad. Multiplication of the pest is favoured by high humidity and a temperature of 70-80°F. The pest is more destructive to American cottons than to indigenous types. Pink bollworm causes shedding of buds, flowers and young bolls.
Older bolls are not generally shed, but they are rendered completely or partially useless; the cotton obtained from partially damaged bolls is poor in ginning and spinning qualities and the oil content of the seeds is low.
The pest is kept under control by a few parasites, but none of them is fully effective in eliminating infestation. In areas in which resting larvae are found in un-ginned cotton and soil, the following control measures may be adopted – (1) sowing early ripening cottons; (2) picking all cotton as early as possible and removing all plants from the field immediately after the last picking; (3) ginning seed cotton 8-10 weeks before the monsoon sets in; and (4) allowing no cotton plant, cotton stick or stump and no alternate host plant to remain in the field during the off season.
In Madras, removal of cotton sticks and all cotton before the first of August is made compulsory by the Madras Agricultural Pests and Diseases Act of 1919, enacted primarily to control stem weevil.
In areas where the pest passes the resting stage in the fallen material, rejected bolls or ginned seed, the following measures are recommended – (1) the fallen material, unpicked bolls, etc. should be burnt before May; (2) cotton seed should be treated to a temperature of about 60° for c. 5 min. by exposure to the sun in May for a day or two in thin layers or by passing it through a Simon heater, as in Egypt.
Jassids or Leaf hoppers (Empoasca devastans Dist.) cause considerable damage to American cottons, particularly in Punjab. Cambodia cottons in Madras are fairly resistant while indigenous cottons are unaffected. The insect sucks the cell sap from leaves. The leaves get curled, develop a reddish tinge from the margin inwards and ultimately dry and drop down. Attacked plants do not bear fruit; even if they do, fruiting is subnormal.
There is a close association between hairiness of the under surface of leaves, particularly the length and density of hairs, and jassid resistance. Isolation of resistant strains is the most effective method of combating jassid incidence. Among the strains evolved, 4-F, L.S.S. and 289-F-43 in Punjab, Parbhani-American in Hyderabad, Buri-107 in Madhya Pradesh and Cambodia in Madras are less susceptible to jassid attack.
An American cotton, Strain-1821, evolved in Madras, is reported to be resistant to jassid under varied conditions of season and soil. The pest can also be controlled by spraying the crop with 0.2% DDT solution or dusting with 10% DDT powder. Spraying with a mixture of DDT and BHC in equal proportions ensures freedom also from aphis attack.