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Crop

- Cultivation
- Yields
- Cotton pests and diseases
- Glossary

Cultivation

Cotton is primarily grown in dry tropical and subtropical climates at temperatures between 11°C and 25°C. It is a warm climate crop threatened by heath or freezing temperatures (below 5°C or above 25°C), although its resistance varies from species to species. Excessive exposure to dryness or moisture at certain stages of the plant development (lasting 5 to 7 months) may be detrimental to cotton quality and yields, and might also kill the plant.

The seeds should be planted in well-prepared moist soil with high nutrient supplying capacity. Indeed, the cotton plant is particularly weak and its moisture and nutrient uptake is remarkable. Cotton production tends to exhaust the soil, which may require some soil management practices typically by means of physical adjustments, fertilisation, and crop rotation (notably with a culture of leguminous plant and one of cereal). Moreover, the root system of the cotton plant is particularly developed and penetrates downward deeply (its depth can sometimes double the height of the surface stem). Accordingly, cotton should be planted in rich seedbeds that are muddy or argillaceous-sandy, where the taproot would grow downward deeply and develop under favourable conditions. Seedling emergence can occur between one week and a month after planting. During this phase (germination, emergence and seedling growth), the plant needs warm temperature and much moisture (7,000 to 9,000 m3 by hectare), which can be supplied by nature or by means of irrigation. Cotton leaves are about 12-15 cm in length and width. They develop along the main stem in a spiral arrangement. Each new leaf commonly develops 5 to 8 cm above the preceding leaf.

Flowering generally starts one month and a half to two months after the crop is planted. Blooming will continue regularly for several weeks, even months, as long as growing conditions are suitable. After flowering, the inner part of the bloom gradually develops into a fruit (called "cotton boll"). Cotton bolls keep growing until full size (approximately 2 to 3 cm width). It will take about two months between the blooming of the flower and the first opening of the bolls.

Cotton bolls burst open upon maturity, revealing soft masses of fibres. Cotton harvesting is then possible (the relevant timeframe is detailed in the table below, to which the reader is referred). The cotton is picked either manually or mechanically. Manual picking is a very labour intensive and time-consuming task, and may be rather expensive. However, it generally produces quality lint with limited amount of trash, since cotton bolls are picked by hand as they burst open upon maturity. Cotton is harvested mechanically by cotton pickers (the most commonly used) or cotton strippers, which remove all the cotton bolls. Cotton strippers are generally used after application of a defoliant. Mechanical harvesting is faster than the manual picking of cotton. However, unwanted leaves and twins may be collected with the cotton. Cotton picked by a stripper might thus need additional cleaning (sorting of the trash) in order to obtain quality lint. Once the cotton is picked (either mechanically or manually) it is transported to a cotton gin, where the cotton fibres (lint) are separated from the cottonseeds. The cotton lint is then compacted in bales and stored.

Especially in the United States, cotton is increasingly grown as "irrigated" cotton. Although irrigated cotton farming tends to be more expensive than "dry land" cotton (which relies on rainfall), it generally produces higher quality lint with greater uniformity and yield potential. Moreover, the maturation period tends to be shorter than for dry land cotton.

Planting and harvesting times for cotton, by producing country

The cotton season conventionally starts on the 1st of August each year.

	Planting period
	Harvest time

Source: UNCTAD secretariat, based on Dagris and ICAC information

For further information, please refer to:
- Cotton with Special Reference to Africa (A. N. Prentice): chapter 10 - the physical environment: climate and soil, 1972.

Yields

World cotton yields (seed cotton and cotton fibre), 1961 - 2003

Source: UNCTAD secretariat (Data: Food and Agriculture Organisation (FAO) for seed cotton; the International Cotton Advisory Committee (ICAC) for cotton fibre)

World annual yield production of seed cotton has increased in a constant manner since the early 1960s, except during the decade 1990's where it remained relatively unchanged. Yields in seed cotton rose from 858 kg/ha in 1961 to 1,760 kg/ha in 2003.

While during the 1960-1980 yields in developed countries were on average more than twice and a half those of developing countries, since the beginning of the 1980s the gap has increasingly narrowed, up to a ratio of 1.3 in 2003. Much of the rise in developing countries' share can be attributed to improved yields in China, mainly as a result of investment in research and innovation. Cotton fibre production and yields have also grown considerably. Over the period 1961-2003, fibre output per hectare (world average) grew from 314 kg to 619 kg, with an average increase of about 1.8% per year. Developing and developed countries have followed the same pattern of convergence as for seed cotton.

The five largest producers in the period 1961-2003 were, by order of importance, China, the United States, the Commonwealth of Independent States (Uzbekistan in particular), India and Pakistan. Since the beginning of the 2000s, China recorded higher yields per hectare compared to the other countries with an average of 3,400 kg/ha for seed cotton and 1,080 kg/ha for cotton fibre (about one time and a half the yield in the United States over the same period).

Cotton yields (kg/ha), China

Productivity increased sharply in China during the period 1961-1966, when seed cotton yields per hectare rose from 620 kg to 1,425 kg (with an increase of about 130% in five years) and fibre output per hectare moved from 259 kg to 345 kg. But since then productivity had been flat, at least up to the early1980s, when seed cotton yields increased by more than 5.5 (reaching 3,467 kg per hectare in 2003) and output levels rose by more than 4 for cotton fibre (1,058 kg/ha in 2003).

	1960	1970	1980	1990	2000	2003
Seed cotton yields (kg/ha)	1097	1366	2218	2610	3398	3467
Cotton fibre yields (kg/ha)	310	450	715	844	1082	1058
Ginning output (%)	29	33	32	33	32	31

Source: UNCTAD secretariat (Data: ICAC)

Cotton yields (kg/ha), former Soviet Union

Over the period 1961-1991, the former Soviet Union was able to produce higher cotton yields per hectare than the other major cotton producing countries, with an average of 2,562 kg/ha. Since the collapse of the Soviet state, productivity has been flattening. The annual average output over the period 1992-2003 was approximately 2,035 kg/ha, that is, it declined by approximately 500 kg/ha per annum.

	1960	1970	1980	1990	2000	2003
Seed cotton yield (kg/ha)	2206	2764	2672	2197	1914	1758
Cotton fibre yield (kg/ha)	742	861	775	695	611	592
Ginning output (%)	34	31	29	32	32	34

Source: UNCTAD secretariat (Data: ICAC)

Cotton yields (kg/ha), India

Indian yield had remained constant over the period 1961-2003, with an average yield of 639 kg/ha for seed cotton and 189 kg/ha for fibres.

	1960	1970	1980	1990	2000	2003
Seed cotton yield (kg/ha)	396	469	547	711	654	751
Cotton fibre yield (kg/ha)	123	146	207	301	310	312
Ginning output (%)	31	31	38	43	47	42

Source: UNCTAD secretariat (Data: ICAC)

Cotton yields (kg/ha), United States and Pakistan

United States and Pakistan were respectively the second and fourth major world producers, with a respective output of 8 and 3 million tonnes of cottonseed. However, their productivity rate (1,846 kg/ha for the United States and 1,602 kg/ha for Pakistan) did not depart significantly from the world average (1,576 kg/ha over the period 1961-2003).

		1960	1970	1980	1990	2000	2003
Seed cotton yield (kg/ha)	United States	1472	1403	1709	1879	1945	2070
	Pakistan	835	934	1329	1728	1821	1818
Fibre yield (kg/ha)	United States	543	520	639	724	731	757
	Pakistan	268	307	422	568	625	617
Ginning output (%)	United States	37	37	38	39	38	37
	Pakistan	32	33	33	33	34	34

Source: UNCTAD secretariat (Data: ICAC)

Although cotton production in Africa is not significant on a global scale, a large number of African countries remain heavily dependent on cotton. For example, cotton accounts for 60% of foreign exchange earnings in Mali. Between 1961 and 2002, West African countries reported cotton yield per hectare at approximately 890 kg. Yields have been rising over the reference period, reaching approximately 1,400 kg per hectare in 2002, up from 275 kg/ha in 1961, with an annual productivity growth of around 5% (close to the productivity growth rate in China (5.3%) or Brazil (4.9%)). Cotton production and productivity levels vary considerably among African countries. Besides West African countries, the case of Egypt deserves special consideration. Indeed, production and productivity levels were remarkably higher in Egypt than in any other African cotton producing country. Egypt accounted for one third of total output in Africa between 1961 and 2002, producing nearly 1.1 million tonnes of cotton over the reference period. In terms of productivity, between 1961 and 2002 its yield per hectare was at 2,230 kg, that is to say, Egypt produced per hectare more than double the cotton of the best performing African country. This performance originates in the fact that cotton is grown under irrigation in Egypt, a way of cultivation that is generally not used in West Africa. By contrast, Nigeria, Tanzania, and Chad performed weakly, with an annual yield ranging between 400 and 500 kg/ha on average over the period 1961-2002. Even though the annual growth rate has been significant (ranging between 4% and 5%), yield per hectare was set at nearly 600 kg in 2002.

Cotton yields (kg/ha), Francophone Africa

	1960	1970	1980	1990	2000	2003
Agricultural output (kg/ha)	436	692	1014	1008	952	988
Cotton fibre yield (kg/ha)	197	267	390	417	407	391
Output at cotton gin (%)	45	39	38	41	43	40

Source: UNCTAD secretariat (Data: ICAC)
Note: The analysis draws on figures for nine francophone African countries: Benin, Burkina Faso, Ivory Coast, Mali, Senegal, Togo, Cameroon, Central African Republic, Chad.

Cotton pests and diseases

Cotton pests

Cotton insects are the principal cause of yield losses. Estimates indicate that the yield losses due to insect infections would amount to almost 15% of world annual production.

More than 1300 different species of insect pests attack the crop. Among the most common and endogenous species found in cotton fields are:

• The pink bollworm (Pectinophora gossypiella) was first described in 1843 by W.W. Saunders as Depressaria gossypiella, from specimens found to be damaging cotton in India in 1842. The pink worm withdraws nutrients from the inside of the cottonseed and may cause serious yield losses. Although the most sever infestations have occurred in Africa and India, the pink bollworm has been recorded in nearly all cotton-producing countries and is a key pest in many of these areas. Infestations may be reduced by the heating of cottonseeds at about 55°C, as well as by other management tactics, including plantation treatment and destruction of the infested crop.

• The boll weevil (Anthonomus grandis), also known as bollworm, is most common in American cotton plantations.

• The Egyptian (spiny) bollworm (Earias insulana) and the red bollworm (Diparopsis castanea) feed on the developing cotton bolls.

• Cotton stainers (Dysdercus superstitious) attack maturing cotton bolls and seeds. They may cause the staining of the lint. In addition, feeding wounds may allow the entry to the boll of saprophytic fungi (organisms which draw nutrients from the host, but do not harm it, contrary to parasites).

• Other insect pests of cotton, such as the white flies (Bemisia gossypiella), may adversely affect lint quality and yield potential. They suck sap from leaves and pose the most serious threat in India and Africa.

• The cotton aphid (Aphid gossypii), also known as the melon aphid, infests the cotton seedlings. Cotton aphids are among the most injuring insects found in cotton. They suck sap from leaves and secrete honeydew* on the undersides of leaves. Honeydew secretions may burn the leaves and interfere with photosynthesis. In addition, aphid is a vector of viruses and a carrier of other insects. In Africa, aphid infestations are among the most injuring insect pests in terms of economic yield lost.

• Nematodes: There are approximately 128 species of nematodes associated with cotton. Five parasitic forms pose the most serious threat to the crop, including the Meloidogyne incognita (or root knot nematode) and the Rotylenchulus reniformis (or reniform nematode). These two species can become serious pests (in the United States, particularly in the State of Virginia, they accounted for 99% of the damage caused by cotton parasitic nematodes). These parasites live in the soil (the root knot nematode favours rough and arenaceous* soil) and withdraw nutrients from the plant roots. Symptom patterns associated with nematodes include stunting, potassic deficiency or early maturity. Nematodes can reduce yields (in Alabama, United States, yield losses are estimated to average 10% or 20%, but can peak to 50% in arenaceous dry soil). Also, depending upon the stage of development of the infested crop, they can hamper the quality of cotton. Root knot nematodes do produce plant damage symptoms that are rather easy to recognise, such as the yellowing or whitening of normally green plant tissue because of a decreased amount of chlorophyll. Damage symptoms caused by other kinds of nematodes (for example, the reniform nematode) are more difficult to detect, since they are generally small and sparse. Besides the direct damage, nemitodes are also an important factor in the incidence of Fusarium and other wilts of cotton. Nematodes may be controlled by cultural practices, such as crop rotations, soil tilling, and use of resistant varieties, or by chemical treatment through nematicides. The two types of nematodes seldom coexist in the same fields.

Certain species are endemic to specific areas of the world. For more information on these types of cotton pests, please refer to the following website:

- Parasitic problems, two new Thysanoptera, insect pests of the cotton plant in Ivory Coast: French Agricultural Research Centre for International Development

More information on cotton pests at:

- Insects associated with Gossypium hirsutum: United States Department of Agriculture, Agricultural Research Service, Southern Plains Agricultural Research Center (SPARC), Crop Germplasm Research Unit

- Cotton (P.M. Phipps, Extension Plant Pathologist, Tidewater AREC): Virginia Cooperative Extension

- Pest Management: National Cotton Council of America (in particular, the section on nematodes)

- Nematode: French National Institute for Agricultural Research

- Nematodes in Cotton in Alabama: William Gazaway, Extension Plant Pathologist, Professor, Plant Pathology, Auburn University

- Cotton with special reference to Africa (A. N. Prentice) : chapter 12 - Cotton pests and diseases, 1972.

- Cotton facts: International Cotton Advisory Committee and Common Fund for Commodities (2003)

Most common diseases in the cotton plant

• Bacterial blight of cotton, also called angular leaf spot (Xanthomonas malvacearum) is favoured by wet weather (temperature above 25°C and relative humidity exceeding 85%). Disease incidence is higher in plants with injured tissues (due to insect pests or cold temperatures). The disease causes stunting and yellowing of the leaves (mainly lower leaves). As diseases progresses, it may result in defoliation. Affected bolls are smaller than normal and exhibit small black spots on their surface. Bolls may fail to open or produce bad quality lint.

• Boll rot (Diplodia gossyina, Colletotrichum spp., Fusarium spp.) attacks lower bolls near maturity. Warm, humid conditions favour the disease. Affected bolls are dark brown, with a white to salmon-pink overgrowth. The fungus is capable of giving a brownish tint to the lint. This disease is a stress-related one, in the sense that it infects plants that have been previously damaged by insect pests. Management practices include seed treatment, as well as the use of resistant varieties.

• The Verticillium dahliae, a common soil inhabitant, penetrates though roots and grow up along the stem tissue. The fungus is favoured by cooler temperatures, excessive soil moisture and excessive soil nitrogen levels. Symptoms first appear on the lower leaves, which turn yellow. Larger plants are stunted (as diseases progresses, defoliation may occur), whereas younger seedlings may die.
Management strategies include proper management of irrigation and the selection of resistant varieties. Under conditions favourable to the development of the disease, yield reductions of up to 30% are possible.

• Seedling diseases (fungi Rhizoctonia solani, Pythium spp.) cause seed and root rotting. In the case of Rhizoctonia solani, girdling of the stem at ground level is observed. Pythium spp. is characterised by the similar symptom patterns, with a water soaked lesion at the soil line.

• Fusarium wilt (Fusarium oxysporum, F. vasinfectum) was first discovered in the United States in 1892, in Egypt ten years later. Wet weather conditions (temperature above 23°C and relative humidity exceeding 85%) are particularly conducive to disease development. Disease incidence can be higher in plants with injured tissues (for example, plants damaged by nematodes). Plants can be affected by the disease at any stage during the season. The vascular tissue of infected plants exhibits a brown/chocolate discolouration through the main stem. Infected water-conducting stem tissues become inactive, causing wilted foliage. Plant death, wilting, yellowing and defoliation are typical of disease symptoms. Leaves turn yellow between veins and eventually shed to leave bare stems. Once the fungus has colonised the plant (diagnosis is confirmed by splitting the stem to reveal dark brown), it most likely causes the death of the host. There is no commercially viable way to eradicate the disease once established (apart from soil fumigation, which is excessively expensive). The impact of the disease may nonetheless be reduced by the use of varieties with high levels of resistance to Fusarium wilt, or by avoiding crop stresses such as over-irrigation and over-application of nitrogen. Fusarium wilt is now an important constraint to sustainable cotton production, especially in Australia.

• Of all diseases known to occur in cotton, cotton root rot (Phymatotrichum omnivorum) is one of the most destructive and difficult to control. The fungus lives in alkaline soils low in organic matter. It occurs only at elevations below 1500m. The fungus has unique biological characteristics that contribute to management difficulties. First of all, Phymatotrichum omnivorum has a remarkably wide host range (infecting over 2300 species alongside cotton), although it attacks only mature plants and does not easily spread from field to field. Second, the fungus survives for long periods of time in the soil (much of the fungus is found as deep as 60cm to 2m in soils). This explains why fungicides are not effective treatment. The fungus is only active when air and soil temperatures are high (respectively above 40°C and 27°C). When environmental conditions are conducive to its development, the fungus invades the pants through their root system. Infected plants can die in two weeks. The first disease symptom is slight yellowing of the leaves, which then quickly turn to a bronze colour and begin to wilt.

For further information on diseases in cotton, please refer to:

- Pest management in cotton: The State of Queensland (Department of Primary Industries and Fisheries)

- Cotton Diseases: The Bugwood Network, University of Georgia, College of Agricultural and Environmental Sciences and Warnell School of Forest Resources

- Cotton Home Page: University of Georgia, College of Agricultural and Environmental Sciences, in particular:
    • Disease and Nematode Management in Georgia Cotton: University of Georgia, College of Agricultural and Environmental Sciences,
    • Cotton diseases and nematodes management: University of Georgia, College of Agricultural and Environmental Sciences.

- Cotton - Gossypium hirsutum: Texas A&M University, Department of Plant Pathology and Microbiology

- How to Manage Pests (Cotton): University of California, Agriculture and Natural Resources (UC IPM - Statewide integrated pest management guidelines)

- Cotton facts (M. R. Chaudhry, A. Guitchounts) : Comité consultatif international sur le coton et Fonds commun sur les produits de base, 2003

- Cotton with special reference to Africa (A. N. Prentice) : chapter 12 - Cotton pests and diseases, 1972.

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Glossary

Honeydrew: "Liquid excretions of Homoptera, consisting largely of sugars and amino acids. Honeydew causes a scorching of leaves, the photosynthetic activity of which is reduced by the presence of sooty moulds" (French National Institute for Agricultural Research).

Arenaceous: Sandy.