24th July 2020




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:

  1. Guinea grass
  2. Spear grass
  3. Siam weed
  4. Wild spinach
  5. Goat weed
  6. Elephant grass
  7. Sword grass
  8. Lemon grass
  9. Mauna grass
  10. Centrosome grass
  11. Bahamas grass
  12. Northern gamba grass
  13. Chick weed
  14. Dandelion
  15. Mistletoe
  16. 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.

  1. 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.
  2. They reduce the quality and market value of farm products and so the farmer’s profit is reduced.
  3. Some weeds are poisonous to farm animals (Cattle).
  4. They may attract pest and diseases which become quite difficult to control.
  5. They compete with planted crops for space.
  6. 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:




Mechanical methods

  1. 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.

  1. 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.

  1. Cultural Weed Control Methods

This involves the use of various farm operations to suppress the growth of weeds. Cultural practices include the following:

(a) flooding

This is the supply of excess irrigation water to a farmland to suppress perennial weeds with underground roots.

(b) Burning

This involves setting the farm land on fire during land preparation.

(c) Mulching

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.

Crop Rotation

This involves growing different crops on a farmland in a circle or in different seasons to prevent weeds that attack certain crops from surviving.

  1. Mechanical Weed Control Methods

These can be done in the following ways

(a) Hoeing

This is the use of a hoe to remove weeds from theirs roots or to bury them completely in the soil.

(b) Slashing

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


  1. Mention 3 weed control measures.
  2. Mention 3 problems caused by weeds to farmers.

Name 10 common weeds.