Cotton

I

Introduction

Cotton, natural vegetable fibre of great economic importance as a raw material for cloth. Its widespread use is largely due to the ease with which its fibres are spun into yarns. Cotton's strength, absorbency, and capacity to be washed and dyed also make it adaptable to a considerable variety of textile products.

II

Cotton Plants

Cotton is produced by small trees and shrubs of a genus belonging to the mallow family, which also includes hibiscus, hollyhock, and the common mallow. The immature flower bud, called a square, blooms and develops into an oval fruit called a boll that splits open at maturity, revealing a mass of long white hairs, called lint, that cover the numerous brown or black seeds. When fully mature and dry, each of these hairs is a thin flattened tubular cell with a pronounced spiral twist, and is attached to a seed. The length of the individual fibres ranges from 1.3 to 6 cm (y to 2y in). Shorter fibres that grow from the seeds are called linters.

Several species are grown commercially; these range from a small tree of Asia, to the common American Upland cotton, a low, multibranched shrub that is grown as an annual. Another species includes the long-fibre Egyptian and Sea Island cottons botanically derived from an Egyptian species. Sea Island cotton thrives in the unique climate of the Sea Islands, located off the south-eastern coast of the United States, and on the islands of the Caribbean such as Barbados. As with Egyptian cotton, the fibre is white and lustrous but its length is greater than that of any other type of cotton, which permits the spinning of extremely fine yarns. Pima, originally called American-Egyptian cotton, is a hybrid type.

It is almost impossible to determine the native distributions of the various species of cotton. Scientists have determined that fibre and boll fragments from the Tehuacán Valley of Mexico are about 7,000 years old. The plant has certainly been grown and used in India for at least 5,000 years and probably for much longer. Cotton was used also by the ancient Chinese, Egyptians, and indigenous inhabitants of North and South America.

III

Cultivation

Successful cultivation of cotton requires a long growing season, plenty of sunshine and water during the period of growth, and dry weather for harvest. In general, these conditions are met within tropical and warm subtropical latitudes in the Northern and Southern hemispheres.

Production of the crop for a given year usually starts soon after harvesting the preceding autumn, when many cotton farmers chop or shred the stalks with machines. The residue is ploughed under and the land usually left rough until spring tillage. Planting time in spring varies from the beginning of February to the beginning of June.

A number of methods, chemical and mechanical, have been used to control weeds and grass, including intensive spraying of herbicide before and after planting. The cultivator, rotary hoe, and flame cultivator are also used to destroy weeds.

Mechanical pickers are used extensively in irrigated lands. The picker has vertical drums equipped with wire spindles that engage and pull the cotton from open bolls.

IV

Cotton Insects and Diseases

In addition to the flowers, the underside of each leaf of the cotton plant contains a small cup-like structure holding nectar. These deposits and the succulent stem make the plant attractive to a variety of insect pests. Chief among these is the boll weevil. The use of early-maturing strains of cotton plus the application of several chemicals and control methods have greatly reduced losses from boll-weevil infestation. The bollworm, the pink larva of a small moth, is believed to have been a native of India but is now parasitic on cotton throughout the world. The larvae burrow into the bolls and eat the seeds. Quarantine, fumigation of seed, and destruction of waste removed from the cotton in ginning are control measures. The bollworm-tobacco budworm is also one of the most damaging cotton pests in terms of losses and control costs. Armyworm, thrips, lygus, and red spider are among other significant pests.

Among the serious diseases to which the cotton plant is subject is the wilt caused by a fungus which enters the roots from the soil and manufactures a poison. No treatment is known, but wilt-resistant strains of cotton have been developed. Another fungus disease is boll rot or anthracnose, caused by sac fungus. The best control is using seed from fungus-free fields.