Subject : Agricultural Science
Topic : DEFINITION AND CHARACTERISTICS OF WEEDS
Class : Basic 8 / JSS 1
Term : Third Term
Week : Week 6
Instructional Materials :
- Pictures of weeds
- samples of weeds
- Scheme of Work
- Online Information
- 9 Year Basic Education Curriculum
Previous Knowledge :
The pupils have previous knowledge of weeds in their previous lessons
Behavioural Objectives : At the end of the lesson, the pupils should be able to
- say the meaning of pests
- mention methods of pest controls
- enumerate the characteristics of pests
- list economic importance of pests
- Meaning of Pest
- Type of Pests
- Classification of Pests based on Mouth Parts
- Classification of Insect Pests based on the Location
Meaning of Pest
Pest can be defined simply as any living organism, plant or animal, which can cause damage to cultivated crops, animals and human beings.
Human beings can also be called pests if they cause damage to crops or livestock.
Pests can carry organisms that cause diseases and constitute nuisance to agricultural products.
Majority of crop pests are invertebrates e.g. insects and eel-worms.
Classification of Agricultural Pests
These are the most common pests of crops all over the world. Insects are animals without backbone and they belong to a group of animals called arthropods (animals with segmented bodies).
Pests eat up whole parts of plants, for example grasshoppers eat up the leaves of crops and so they are described as defoliators.
Insects destroy crops by feeding on them.
Insect pests can be classified based on
(i) their mouth parts (feeding habit).
Classification of Insect Pests based on Mouthparts
Based on their mode of feeding, insect pests can be divided into three groups:
- Piercing and sucking insect pests
- Biting and chewing insect pests
- Boring insect pests
1. Piercing and Sucking Insect Pests
These insects have mouth parts modified to pierce and suck the sap from tissue of tender crop plants. They possess stylets and proboscis with which they pierce and suck plant sap or juice. In the process, they are transmit diseases to them and reduce the growth of the plants.
Examples are white flies, aphids, mealy bug, cotton stainer, thrips, moth, scale insects, capsids, green spider mites etc.
2. Biting and Chewing Insect Pests
The mouth parts consist of mandibles, maxillae, labium and labrum. They feed on the leaves and young stems of plants by biting and chewing.
Examples are locusts, grasshoppers, termites, mantis, army worms, caterpillars (larva stage of butter flies), crickets.
3. Boring Insect Pests
The mouth parts are modified into rostrum used to bore holes into plant tissues and seeds.
The grains that are kept in the store are damaged by weevils. They use their long mouth part to bore holes into the grains and reduce them into powder. The damage done by these boring pests reduce crop quality and their market value.
Examples are weevils, stem borers, beetles, cotton boll worm etc
Classification of Insect Pests based on the Location
Based on their location, insect pests can be divided into three groups:
- Field pests
- Field to store pests
- Storage pests
- Field pests: These are pests that attack the growing crops on the field.
Examples are grasshopper, mealy bug, locust etc.
- Field to store pests: These are pests that attack the crops from the field and then accompany them to the store house.
Examples are maize weevil (Sitophilus maydis), rice weevil (Sitophilus oryza), beans or cowpea beetle (Callosobruchus maculatus)
- Storage pests: They are the pests that attack the stored produce.
Examples are maize weevil, rice weevil, yam beetle, bean or cowpea beetle, etc.
Non-insect Pests/Vertebrate Pests
These are bigger pests with backbone. They are few in number when compare to insect pests. They attack crops on the field while some e.g. rats attack store products.
Examples of vertebrate pests include:
- Mammals: They contaminate grains with feaces and urine and transmit diseases e.g. rodents (grasscutter, squirrels, mice, rats, wild rabbits etc.), monkey, goat, sheep, lizard.
- Birds and bats: They are important pests of cereals and fruit crops e.g. weaver birds, bush fowl, doves, parrots, fruit bat etc.
- Snail: They are non-mammal pests that feed on leaves of plants especially seedlings and vegetables thereby, reducing their photosynthetic ability.
- Nematodes are worms that live in the soil e.g. eel worm.
The topic is presented step by step
The class teacher revises the previous topics
He introduces the new topic
The class teacher allows the pupils to give their own examples and he corrects them when the needs arise
- Define the term pest.
- List two piercing and sucking insect and three biting and chewing insect pests
- List four general methods of controlling weeds.
- Explain how mulching and crop rotation can be used to control weeds.
- Differentiate between pre-emergence and post-emergence herbicides
- State five uses of weeds
- Define the term pest.
- List the groups of insect pests based on their mouth parts and give two examples of each.
- Give one example of storage pest of cowpea.
- Give two examples of weeds that can be dispersed through explosive mechanism.
The class teacher wraps up or conclude the lesson by giving out short note to summarize the topic that he or she has just taught.
The class teacher also goes round to make sure that the notes are well copied or well written by the pupils.
He or she does the necessary corrections when and where the needs arise.
Prepare for the next lesson by reading about
CLASSIFICATION OF WEEDS