Weed





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.

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
exotics (or exotic invasives). This term is applied when a plant is an
introduced foreign plant that then invades and disturbs natural ecosytems,
displacing species native to the target ecoregion.

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 have caused 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:

   * Dandelion
   * Giant salvinia
   * Goutweed
   * Japanese knotweed
   * Kudzu
   * Water hyacinth

   * and many more

Weed is also common slang for marijuana.