| Revision as of 17:12, 6 March 2004 view sourceMarshman (talk | contribs)Extended confirmed users9,354 edits Add in minimal text taken from Noxious weed← Previous edit | Revision as of 13:48, 11 March 2004 view source MPF (talk | contribs)Extended confirmed users42,236 edits Weed, CANext edit → | ||
| Line 1: | Line 1: | ||
| ''This article is about unwanted plants. Other meanings: ] and ].'' | ''This article is about unwanted plants. Other meanings: the town of ]; ] and ].'' | ||
| ---- | ---- | ||
Revision as of 13:48, 11 March 2004
This article is about unwanted plants. Other meanings: the town of Weed, California; Weed music distribution service and Marijuana.
Weed is the generic word for a plant growing in a spot where it is not wanted. The most prominent use of the word is in connection with farming, where weeds may damage crops when growing in fields and poison domesticated animals when growing on pasture land. Many weeds are short-lived annual plants, that normally take advantage of temporarily bare soil to produce another generation of seeds before the soil is covered over again by slower growth; with the advent of agriculture, with extensive areas of ploughed soil exposed every year, the opportunities for such plants have been greatly expanded.
Noxious weeds
A Noxious weed is a plant that is growing in such a manner that it is causing problems by interfering with other desirable plants or contaminating the harvest of useful plants. Noxious weeds are especially problematic weeds because they spread rapidly, are hard to kill, are toxic to cattle and/or humans, or cause other serious problems. Generally (but not always) noxious weeds are invasive species. In the US and Canada, government agencies, usually within the federal, state or provincial departments of agriculture maintain lists of noxious weeds, and the term has legal significance. It is usually unlawful to transport these weeds or their seeds.
The teasel, for example, was a plant widely grown because it was used to manufacture woolens. It is no longer needed for this purpose but grows everywhere ("Growing everywhere" does not make it a noxious weed). Thus it has become a noxious weed.
Invasive species
Other plants have become weeds by being transferred by human action to locations where they have no natural grazing predators; the classic case is the prickly pear (Opuntia stricta), which overran vast areas of Australia until a moth, Cactoblastis cactorum was introduced. This is frequently quoted as the classic example of successful biological pest control, eliminating >90% of the prickly pear infestation within 10 years.
In cases like the prickly pear in Australia, the weeds are termed invasive species (or exotic invasives). This term is applied when a plant is an introduced species that invades and disturbs natural ecosytems, displacing species native to the target ecoregion and causing harm.
Control
In order to reduce weed growth many weed control strategies have been developed. The most basic is ploughing, which cuts the roots of annual weeds. In modern times, chemical weed killers known as herbicides have been widely used; they have caused some environmental damage, and efforts are being made to reduce the use of such substances (see for example genetic engineering, organic gardening).
Plants that are often considered weeds include:
- and many more
See also: weedy species, weed control, herbicide, pesticide