Herbicides and Plant Physiology. Andrew H. Cobb. Читать онлайн. Newlib. NEWLIB.NET

Автор: Andrew H. Cobb
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Биология
Год издания: 0
isbn: 9781119157700
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      One year’s seed is seven year’s weed.

      A traditional rhyme

      The human race has been farming for over 10,000 years. Weeds have been an unwelcome presence alongside crops ever since the first farmers saved and planted seeds in the region that is now present‐day Turkey and the Middle East. Indeed, when these early farmers noticed a different plant growing, decided they did not want it and pulled it up, they were carrying out a form a weed control that is still used today: hand roguing.

      But what are weeds? Weeds are all things to all people, depending on the viewpoint of the individual. To some they are plants growing where they are not wanted; to others they are plants growing in the wrong place, in the wrong quantity, at the wrong time; and to some they are regarded as plants whose virtues have yet to be fully discovered! The need to control weeds only arises when they interfere with the use of the land, and this is usually in the presence of a crop, such as in agriculture and horticulture. Weed control may also be necessary in other situations including amenity areas, such as parks and lawns, in water courses, or on paths and drives where the presence of plants may be regarded as unsightly. It should not be overlooked, however, that weeds contribute to the biodiversity of ecosystems and should only be removed when financial or practical implications make their presence unacceptable. With this in mind an appropriate definition of a weed is:

      Any plant adapted to man‐made habitats and causing interference of the use of those habitats. (Lampkin, 1990)

      Or

      A plant whose virtues remain to be discovered. (Emerson, 1912, see https://theysaidso.com/quote/ralph‐waldo‐emerson‐what‐is‐a‐weed‐a‐plant‐whose‐virtues‐have‐never‐been‐discovered)

      Source: Radosevich, S.R. and Holt, J.S. (1984) Weed Ecology: Implications for Vegetation Management. New York: Wiley. Reproduced with permission of John Wiley & Sons.

Number of species classified as the world’s worst weeds (%) Family Examples of major crops Examples of major weeds Common name
44 Gramineae Barley, maize, millett, oats, rice, sorghum, sugar cane and wheat Elytrigia repens (L.) Couch
Alopecurus myosuroides (L.) Black‐grass
Avena fatua (L.) Wild oat
Sorghum halepense (L.) Pers. Johnson grass
Echinochloa crusgalli (L.) Barnyard grass
4 Solanaceae White potato Solanum nigrum (L.) Black nightshade
Datura stramonium (L.) Jimsonweed
Hyoscyamus niger (L.) Henbane
5 Convolvulaceae Sweet potato Convolvulus arvensis (L.) Field bindweed
Cuscuta pentagona (Engelm) Field dodder
Ipomoea purpurea (L.) Roth Tall morning glory
5 Euphorbiaceae Cassava Euphorbia maculata (L.) Spotted spurge
Euphorbia helioscopia (L.) Sun spurge
Mercurialis annua (L.) Annual mercury
6 Leguminosae Soybean Cassia obtusifolia (L.) Sicklepod
Melilotus alba (Desc) White sweetclover
Trifolium repens (L.) White clover

      Most plants grow in communities consisting of many individuals. If the resources available (such as space, water, nutrients and light) become limiting then each species will be forced to compete. Weeds are often naturally adapted to a given environment and so may grow faster than the crop, especially since the crop species has been selected primarily for high yield rather than competitive ability. A unit of land may therefore be regarded as having a finite potential biomass to be shared between crop and weeds, the final proportion being determined by their relative competitive ability.

      Source: Naylor, R.E.L. and Lutman, P.J. (2002) What is a weed? In: Naylor, R.E.L. (ed.) Weed Management Handbook, 9th edn. Oxford: Blackwell Publishing/BCPC. Reproduced with permission