A weed may be defined as any plant or vegetation that interferes with the objectives of farming or forestry as growing crops, grazing animals or cultivating forest plantations.
A weed may also be defined as any plant growing where it is not wanted. For example, a plant may be valuable or useful in a garden, or on a farm or plantation - but if the same plant is growing where it reduces the value of agricultural produce or spoils aesthetic or environmental values, then it is considered a weed. However, some plants are weeds regardless of where they grow
Weeds are interfered with the utilization of land and water resources and adversely affect crop productivity of crops. In a comprehensive term, weed is a plant growing in field other than a croup.
Weeds been well adapted, competitive with crop plants, interfere with agricultural operation an ultimately reduce the economic produce. Some conclude that weeds caused more losses than other form of pests like insects’ diseases, nematodes, rodents etc. Some estimates put as high as 100% yield losses due to weeds.