(a) Define the term weed (b) Describe four methods of weed control. (c) Give six reasons for controlling weeds on the farm.

(a) Weed. A weed is any plant that grows where it is not wanted, that is, a plant growing out of place and competing with cultivated crops for space, light, water and nutrients.

(b) Four methods of weed control:

1. Cultural (mechanical/manual) method: weeds are removed by hand-pulling, hoeing, slashing, mulching, crop rotation, close spacing and good tillage practices.
2. Chemical method: weed-killers (herbicides) such as pre-emergence and post-emergence herbicides are sprayed to kill the weeds.
3. Biological method: living organisms (insects, animals or pathogens) are used to feed on or destroy specific weeds; for example grazing animals or introduced insect predators.
4. Physical method: weeds are destroyed by burning, flooding or by covering (smothering) with materials to deprive them of light.

(c) Six reasons for controlling weeds on the farm:

1. Weeds compete with crops for nutrients, water, light and space, reducing crop yield.
2. Weeds harbour pests and diseases that attack crops.
3. Some weeds are parasitic on crops (for example Striga) and reduce their vigour.
4. Weeds lower the quality and market value of harvested produce when mixed with it.
5. Weeds obstruct farm operations such as harvesting and increase the cost of production.
6. Some weeds are poisonous to livestock, and weeds can cause water loss from the soil through transpiration.