TERM/WEEK: THIRD TERM/ WEEK 4
DATE: 4th July, 2020
CLASS: Grade 4
SUBJECT: Pre-vocational Studies
TOPIC: Weeds: Meaning, Examples, Effects and Control
REFERENCE: Lantern Comprehensive Pre-Vocational Studies Book 5.
By: O. Busari Et. al
A weed is a plant considered undesirable in a particular situation, ‘a plant in the wrong place’.
Notes for the Pupils
Definition of Weeds
A weed is a plant that is growing where it is not wanted. Weeds compete with planted crops for light, space, nutrients and water. Weeds grow very fast and easily crowd the farm or garden, leaving less space for crops to grow well.
Examples of common weeds are:
- Guinea grass
- Spear grass
- Siam weed
- Wild spinach
- Goat weed
- Elephant grass
- Sword grass
- Lemon grass
- Mauna grass
- Centrosome grass
- Bahamas grass
- Northern gamba grass
- Chick weed
- Giant star grass
Effects and Control of Weeds
Problems of weeds to farmers
Weeds have very bad effects on crop growth. Generally, they reduce crop yield. Some specific effects are listed below.
- They compete with crops for light, nutrients and water. This reduces the amount of these resources that are available to plants for their growth, thus reducing crop yields.
- They reduce the quality and market value of farm products and so the farmer’s profit is reduced.
- Some weeds are poisonous to farm animals (Cattle).
- They may attract pest and diseases which become quite difficult to control.
- They compete with planted crops for space.
- Weed control is costly in time and money for farmers.
Weed Control Measures
Removing weeds from the farm or garden helps to ensure that planted crops have enough space, nutrients, water and light to grow.
There are 4 major weed control methods. These are:
- Biological Weed Control Methods
These involves the use of living plants and animals to control weeds. It can be done in the following ways
(a) using suppressive plants
Cover crops such as legumes (e.g. cowpea and groundnut) can be used to suppress the growth of weeds from the farm
(b) Predatory insects that feed on weeds can be introduced to the farm to eat up weeds.
(c) animals that feed on the weed can be allowed to graze on the farm to eat up weeds. Examples are Cattle, Sheep and goats.
- Chemical Weed Control Method
Chemicals that kill weeds are called herbicides. Herbicides kill weeds but not planted crops. They are therefore said to be selective. Some herbicide are applied to the farm before the planted crops germinate. They are called pre-emergent herbicides. Others are applied after the planted crops have germinated and are growing well.
Some herbicides kill weeds as soon as they come into contact with them.
- Cultural Weed Control Methods
This involves the use of various farm operations to suppress the growth of weeds. Cultural practices include the following:
This is the supply of excess irrigation water to a farmland to suppress perennial weeds with underground roots.
This involves setting the farm land on fire during land preparation.
These is the use of dead materials like grass and straw to cover the soil. This chokes weeds and prevents them from growing.
(d) Early Planting
this involves planting crops before weeds begin to germinate.
(e) Close Spacing
This means planting crops with minimal spacing in-between.
Digging soil exposes the roots of weeds which then become dried up and die.
This involves growing different crops on a farmland in a circle or in different seasons to prevent weeds that attack certain crops from surviving.
- Mechanical Weed Control Methods
These can be done in the following ways
This is the use of a hoe to remove weeds from theirs roots or to bury them completely in the soil.
This is the use of a cutlass to remove the parts of weeds above the ground.
(c) Rotary Cultivation
This is the use of ploughs and harrows to bury weeds on the farm
- Mention 3 weed control measures.
- Mention 3 problems caused by weeds to farmers.
Name 10 common weeds.