Tobacco Plant Species
qiazhan English name: Tobacco
Sub Title:
tobacco, common name of the plant Nicotiana tabacum and, to a limited extent, Aztec tobacco (N. rustica) and the cured leaf that is used, usually after aging and processing in various ways, for smoking, chewing, snuffing, and extraction of nicotine. Various other species in the genus Nicotiana are grown as ornamentals, known collectively as flowering tobaccos. This article deals with the farming of commercial tobacco from cultivation to curing and grading.
Cultivation
Though tobacco is tropical in origin, it is grown throughout the world. Cultivated tobacco (N. tabacum) requires a frost-free period of 100 to 130 days from date of transplanting to maturity in the field. Aztec tobacco (N. rustica), which is grown to some extent in India, Vietnam, and certain Transcaucasian countries, matures more quickly and is more potent than cultivated tobacco.
The prime requisite for successful tobacco culture is a supply of well-developed healthy seedlings that is available at the proper time for transplanting. Soil for a plant bed should be fertile and of good tilth and drainage; it must be protected from chilling winds and exposed to the sun. The soil is usually partially sterilized by burning or using chemicals such as methyl bromide (now illegal in many countries) to control plant diseases, weeds, insect pests, and nematodes. The soil must be finely pulverized and level so that the seed can be lightly covered with soil by rolling or trampling. Uniform distribution of seeds is important. In warm regions of the world, the germinating seedlings are produced outdoors in cold frames covered with thin cotton cloth or a thin mulch, such as chopped grass (used in particular in Zimbabwe), straw, or pine needles. Glass or plastic is used in colder regions, and close attention is given to watering and ventilation. After 8 to 10 weeks the seedlings are 10 to 18 cm (4 to 7 inches) in length and are ready for transplanting in the field. Transplanting machines are used extensively in some areas, but much of the world’s tobacco is planted by hand.
Spacing of plants in the field varies widely according to the type of tobacco. Orinoco strains, used for flue curing, are grown in rows 1.2 metres (4 feet) apart, with plants 50 to 60 cm (20 to 24 inches) apart in the row. Varieties in the Pryor group are grown to produce the dark air-cured and fire-cured types and are often planted in hills 1 metre (3.5 feet) apart. Burley and Maryland strains, used for the production of light air-cured tobaccos, may be planted 81 to 91 cm (32 to 36 inches) apart or closer. Broadleaf and seed-leaf strains, including the Havana seed, Cuban, and Sumatra varieties, are used for the production of cigars; they are grown in rows spaced 1 metre (3 feet) apart, with individual plants placed at a distance of 38 to 68 cm (15 to 27 inches) from each other. The variety grown for production of Perique is spaced the widest, with rows 1.5 metres (5 feet) apart and 91 to 107 cm (36 to 42 inches) between plants. Aromatic tobaccos, also used for cigars, are spaced in rows 38 to 60 cm (15 to 24 inches) apart with 8 to 20 cm (3 to 8 inches) between plants in the row.
Soil requirements vary widely with the type of tobacco grown, though well-drained soil with good aeration is generally desirable. Flue-cured, Maryland, cigar-binder, and wrapper types of tobacco are produced on sandy and sandy loam soil. Burley, dark air-cured, fire-cured, and cigar-filler types are grown on silt loam and clay loam soils, with clay subsoils. The need for fertilizer is determined by the type of tobacco, soil, and climate; nitrogen, phosphorus, and potassium are commonly applied as necessary to prevent symptoms of nutritional deficiency.
Large-leaf tobaccos are often topped—that is, the terminal growth is removed—when the plant has reached the desired size, usually at or shortly after flowering. The number of leaves remaining varies widely. Dark air-cured and fire-cured tobaccos may have 10 to 16 leaves, while Burley, flue-cured, Maryland, and cigar types may have 16 to 20 leaves. After topping, the suckers, or lateral shoots, are removed to increase leaf development, providing increased yields. The work may be done by hand, in which case it must be repeated regularly, or by application of sucker-suppressing chemicals. Aromatic tobacco culture differs from that of most of the large-leafed tobaccos in that the plants are rarely topped and preferably are grown on soils of low productivity.
Diseases and pests
Common diseases and pests are black root rot, Fusarium wilt, tobacco mosaic virus (TMV), bacterial leaf spot, downy mildew, black shank, broomrape, and witchweed. These may be controlled by sanitation, crop rotation, the use of fungicide and herbicide sprays and fumigants, and breeding of disease-resistant strains. Some resistant varieties of tobacco have been produced by blending desired characteristics from longflower tobacco (N. longiflora) and N. glutinosa, among others, with strains of commercial tobacco.
Common insect pests are green June beetle larvae, cutworms, and flea beetles in the plant bed and hornworms, grasshoppers, flea beetles, cutworms, budworms, and aphids in the field. The cigarette, or tobacco, beetle damages the stored leaf and sometimes the manufactured product. Insect pests are controlled on the growing crop by using pesticide sprays and dusts, on the stored product by fumigating and trapping. Biological control often is effective. Fumigation controls nematodes in the field.
