What is Weed?
Weeds: Weed is a plant growing where it is not desired; or a plant out of place.
Weeds include all types of undesirable plants such as trees, grasses, broadleaved
plants, sedges, aquatic plants, parasitic plants etc.
Losses from weeds:
Yields may be reduced. Cost of production become high because of intercultural operation for weed. Land values may be reduced due to perennial weeds. Crop choices become limited. Some crops may not compete effectively against heavy weed growth. Root and crop damage may result from weed control operation. Weeds act as alternate hosts to pests in off season which infect the crop later. Aquatic weeds reduced the flow of water in irrigation and drainage channel.
Classification of weeds:
Weeds are three types depending on their life cycle
Annually: these weeds grow and mature within a year. Usually they complete their
life cycle in one season, example most common weeds.
Biennials: These weeds live for two seasons with a duration upto 2 years. In the 1st
year they remain vegetative and in the second year they produced seeds. Example:
wild carrot, wild parsnip.
Perennial: They live for more than two years. Most reproduced by seed and many
are able to spread vagetatively. Example Bermuda grass, nutgrass. What is Weed?
On the basis of morphological characters:
Sedges: Triangular stem, no node, leaf at top, cyperaceae family; no branch. eg.
Broad leaf: broad leaf alternately arrange on stem, cylindrical stem. eg.
Characteristic of weeds:
- Weeds are productive with abundant seed production potentialities. eg. Bothua,
- They are persistent and resistant to their control and eradication.
- Weeds remain dormant and viable for 30 to 40 years. eg. Bothua
- Weeds are hardy and can resist any adverse climatic, disease and soil conditions
- Some of the weeds propagate vegetatively. eg. Cynodon sp (bermuda grass).
- Some weeds are very similar to crop seeds and their separations becomes a
problem. eg. Musterd and Argemone sp.
- Some leguminous weed can grow N2 deficiency unfertile soil.