Weed
From Freepedia
- This article is about unwanted plants. For other meanings see Weed (disambiguation)
Image:Weeds.jpg Weed is the generic word for a plant growing in a spot where it is not wanted. Weeds become of economic significance 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 expanded greatly.
The notion of "wanted" is of course entirely in the eye of the beholder. A weed in one situation might be a wildflower in another. Some people love dandelions for their yellow buttons, like gold coins on the ground. Children enjoy blowing the puffball seed heads that form on the dandelion, and adults might utilize the dandelion root as an herbal medicine. In some areas, dandelion leaves, which are edible, are sold in certain restaurants or grocery stores. Yet the caretaker of a lawn will generally regard the dandelion as a troublesome weed in that situation.
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Noxious weeds
The term noxious weed applies to especially difficult to manage weeds, that cause serious problems. These typically are invasive species that may be difficult to control, or may be a health hazard to humans or to stock animals or to wildlife, or may be otherwise detrimental to an environment. Typically, legislation or government regulation defines certain plant species as noxious and regulations make it an offence to cultivate, transplant, or disseminate the seeds of those species. In some cases it may be an offence even to permit them to grow through inaction (as on one's property).
Invasive species
- See main article at invasive species
Many 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, eliminating more than 90% of the prickly pear infestation within 10 years. This case is frequently cited as an example of successful biological pest control.
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.
Weed control
- See main article at weed 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. However, to the extent that such chemicals leave a harmful residue in the soil, they can produce unanticipated adverse environmental effects, and efforts are being made to reduce the use of such substances (see for example organic gardening).
Other methods of eliminating weeds include covering an area of ground with several layers of wet newspaper or a black plastic sheet for several weeks.
In the case of using wet newspaper, the multiple layers prevent light from reaching all plants beneath, which kills them. Saturating the newspaper with water daily speeds the decomposition of the dead plants. Any weed seeds that start to sprout because of the water will also be deprived of sunlight, be killed, and decompose. After several weeks, all germinating weed seeds present in the ground should be dead. Then the newspaper can be removed and the ground can be planted. The decomposed plants will help fertilize the plants or seeds planted later.
In the case of using the black plastic sheet, the greenhouse effect is used to kill the plants beneath the sheet.
These methods of weed elimination are best for small areas at a time, as this reduces neighbors' tendencies to complain about yard messiness.
A 5-10 cm layer of wood chip mulch on the ground will also prevent most weeds from sprouting. Also, gravel can be spread over the ground as an inorganic mulch.
Plants that are often considered weeds
- Cleaver
- Crabgrass
- Dandelion
- Daucus
- Diffuse knapweed
- Dock
- Eucalyptus
- Giant salvinia
- Gorse
- Goutweed
- Hairy Vetch
- Henbit
- Japanese knotweed
- Johnson Grass
- Kudzu
- Milkweed
- Mullien
- Plantain
- Quackgrass
- Ragweed
- Red deadnettle
- Shepherd's purse
- Sunflower
- Thistle
- Tufted Vetch
- Tumbleweed
- Water hyacinth
- Wild onion
- and many more
See also
- Invasive Plants
- Weedy species
- Weed control
- Herbicide
- Pesticide
- List of plants and fungi which damage buildings
- Slang for drug known as cannabis
