Economic Importance of Weeds
- Weeds grow very quickly on farmlands thereby reducing the nutrients, space, water, and sunlight available for crop development.
- Weed seeds reduce the quality of harvest products. Their seeds in harvested grains reduce the market value of grains and reduce the quality of seeds in storage.
- Some weeds possess toxins (poisonous chemicals) which reduce the quality of forage and can cause the death of farm animals which graze on them.
- Weeds serve as host to pests and diseases of crop plants and this causes economic losses to farmers.
- Weed can injure ruminant animals when they graze on pasture with thorny weeds. Some stick to the skin of the animal while thorny weeds can cause wounds thereby reducing the market value of hide and skin.
Uses of Weeds
- Medicines: The leaves and roots of some selected weeds can be used in the preparation of herbal medicine by traditional healers.
- Food: Weeds like waterleaf provides food for man; Bahamas grass, Tridax, Elephant grass, serve as feed for farm animals.
- Host for beneficial insects: weeds host beneficial insects like bees and also provide nectar for bees. Bees produce honey, bee-wax which can increase farmer’s income.
- Genetic materials: Weeds produce genetic materials which are derived from wild relatives of cultivated plants. This can be used for the varietal development of crops.
- Ornamental purpose: Weeds are used to make lawns and to beautify the environment. An example is the carpet grass.
- Cover crops: Some weeds can be used as cover crops to prevent soil erosion in an uncultivated farmland.
Methods of Weed Control
- Rotation of crops: This involves the cultivation of two or more crops, one after the other on the same piece of land to maintain soil fertility and control weeds on the farmland.
- Use of herbicides: Herbicides are chemical substances used to kill weeds. Knapsack sprayers are used for the application of the herbicides on small farms while Boom sprayers are used on big farms. Herbicide can be of the following types;
- Contact herbicide – they kill the part of the weed they fall on during spraying. Contact herbicides can be selective (kill only weeds on the farm), or non-selective (kill both herds and weeds). Examples are Paraquat, Gesaprin, Disquat, etc
- Systemic herbicides – these herbicides when absorbed by weeds move to their shoot and root systems to kill them. The can as well be selective or non-selective herbicides. Systemic herbicides offer very effective control for perennial weeds like spear grass. Examples are MCPA, 2-4D, etc.
- Pre-emergence herbicide – they are applied to the soil after planting, before the emergence of the crops.
- Post-emergence herbicide – these herbicides are applied after the emergence of the planted crops.
- Hand pulling: This is an example of mechanical control of weeds. Farmers use hoes and cutlasses during hand pulling of weeds on their farm.
- Cover crops: Cover crops such as melon, velvet beans and other cover crops can be planted on the soil to control weeds on the farm.
- Plant quarantine: It involves the close monitoring of imported crops to prevent weed seeds from being introduced into the country or farmlands.
- Highlight five (5) beneficial uses of weeds.
- Explain in your own words any two (2) methods of weed control.