Methods of Weed and Pest Control III – JSS1 Agricultural Science Lesson Note (Second Term)

Insect pests damage crops by biting, chewing, boring and sucking, and they reduce the yield and quality of crops in the field and in store. They can be prevented or controlled through cultural, physical, chemical, biological, prohibition and quarantine measures. This note explains the economic importance of insect pests and the main control methods.

Behavioural objectives

By the end of the lesson, students should be able to:

• state how insect pests damage crops and why they matter economically;
• list the measures used to prevent and control insect pests;
• describe cultural, physical and biological control with examples;
• name the chemicals used for insect control and give examples of each;
• explain what quarantine is.

Why are insect pests economically important?

Insect pests may cause damage to crops in the following ways:

1. Insect pests destroy field crops through their activities such as biting, chewing, boring and sucking.
2. They reduce the viability (germinating capacity) of stored produce.
3. Heavy attack by insect pests may lead to total crop failure.
4. They reduce the market value of crops, especially fruits and vegetables.
5. Control of insect pests increases the cost of production.
6. Some insect pests act as vectors of plant diseases.
7. Insect pests reduce the yield (quantity) and quality of crops, either in the field or in store.

How can insect pests be prevented and controlled?

Generally, insect pests can be effectively controlled through the following measures:

1. Cultural control
2. Physical control
3. Chemical control
4. Prohibition
5. Quarantine
6. Biological control

What is cultural control?

Cultural control is the use of good cultural practices to reduce or destroy insect populations and to help crops escape insect attacks. These practices include:

1. Crop rotation
2. Tillage
3. Early planting
4. Adequate and regular weeding
5. Planting resistant varieties
6. Timely harvesting
7. Burning

What is physical control?

Physical control involves the physical removal of insect pests from the farm. The following methods are used:

1. Hand picking
2. Airtight storage

What is biological control?

Biological control involves the introduction of the natural enemies of the insect pest. The enemies are introduced to feed on the insect pest, which reduces the population of the pest. For instance, ladybirds are introduced into an aphid-infested farm to eat up the aphids.

What is chemical control?

Chemical control is the use of chemicals to protect crops from insect attack. If an attack is already established, the chemicals are used to kill the insect pests at various stages of their life cycles. Chemical control is the most effective method of controlling insect pests. The chemicals used include:

1. Insecticides: These are chemicals specifically used for controlling insect pests. They may be applied as solids such as dust, or as emulsions or sprays. Examples include Gammalin 20, Vector and Aldrin dust.
2. Fumigants: These are insecticides in the form of vapour. They are usually enclosed in airtight containers. Examples include hydrogen cyanide, methyl bromide and ethylene.

What is quarantine?

Quarantine is a period of isolation and observation imposed by law on imported materials, including seeds, plants and animals. The materials are kept long enough to observe them for any disease symptoms. If symptoms are detected, the materials are either destroyed or sent back to the country where they were bought, at the expense of the importer.

Evaluation

1. State four ways in which insect pests damage crops or reduce their value.
2. List the six measures used to prevent and control insect pests.
3. What is biological control? Give one example.
4. What is the difference between insecticides and fumigants?
5. What is quarantine, and what happens to imported materials that show disease symptoms?

Assignment

Write short notes on cultural control and chemical control of insect pests. Give examples in each case.