Weed is a plant growing where it is not wanted, especially among crops or garden plants.
Harmful Effects of Weeds:
- Compete with crops for light, water and nutrients.
- Crowd out the crop plants.
- Decreases the farm product and its market value.
- Poisonous to man and animals.
- Give shelter to harmful insects.
- Hosts pest and disease.
- Increases the cost of cultivation of crop.
Weed Control Methods:
Weed control is the process of limiting weed infestation to assure profitable growing of crops and efficiently conducting all operations necessary for successful cultivation. The concept of Integrated weed management (IWM) involves the planned use of all possible direct and indirect measures to control weed infestation rather than relying on a single method to combat weeds.
Indirect method of Weed Control:
This method reduces weed infestation through two approaches; preventive method and cultural/ecological method.
“Prevention is always better than cure”.
Preventive measures to control weed are.
- Use of clean seed.
- Do not use manure unless the viability of weed seeds has been destroyed.
- Restrict movement of livestock to weed free areas.
- Avoid using soil from weed infested areas.
- Clean farm equipments before use.
- Keep the adjacent lands clean of weeds.
- Keep the farmland under observation.
- Act collectively against wind-borne weeds and seed weeds.
Cultural & Ecological Method:
Cultural and ecological methods are employed to suppress the weed population by decreasing their competitive power or by encouraging weed growth a specified period during which direct weed control measures can be adopted.
Ploughing reduces weed due to burying down of weed seed and harrowing effective in killing germinating weed seeds and small weeds.
Crop rotation not only reduces weed infestation but also sometimes eliminate certain weed species.
Weeds sensitive to anaerobic conditions fail to germinate and eliminate through flooding the field.
Effective for control of aquatic weeds in ponds etc.
Straight row planting helps haw/mechanical weeding.
Crop variety capable of competing with the weed.
Use of artificial mulch such as straw, hay, manure, paper and rice dusk prevents the light to penetrate down to the weed, resulting control of weed.
Allelopathy is the inhibition of germination or growth of weeds through release of certain chemicals into the environment by plant parts (living/dead) which are toxic to weeds. Allelopathy can be achieved through cultivars which release allolochemicals or through mulching that suppresses weed growth through allelochemicals.
Direct Method of Weed control.
This method involves controlling the emergence, growth and reproduction of weeds by attacking them directly. Few common methods are given below;
This is the most effective and safest but labour intensive method of weed control. This method involves pulling out the weeds by hand or by hand hosing, utilizing Khurpa, sickle etc to destroy weed from the field.
Destruction of weeds by using mechanical tools such as “bar harrows” and “cultivators” Intertillage and blind hoeing also effective.
Introduction of animals, insects or diseases which reduce weed population in the field. Human and environment friendly technique. For example, control of prickly spear cactus in Australia by the Argentine moth Borer. Animals like goats, sheep and cattle have also been used for unselected grazing of weed under the fruit trees or during fallow season.
Easy, economical and effective method of weed control but environmentally hazardous. Herbicides may have different modes of action to control the weed. Few examples are given below; Dinoseb: Interfere with protein metabolism. Diuron: photosynthesis inhibitor. Atrazine: Chlorophyll inhibitor.