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

Insect pests are insects that damage crops in the field and produce in store, and they are controlled by cultural, physical, chemical, biological, prohibition and quarantine measures.

Behavioural objectives

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

1. State how insect pests damage crops and why they matter economically.
2. List the measures used to prevent and control insect pests.
3. Describe cultural, physical and biological control with examples.
4. Name the chemicals used for insect control and give examples of each.
5. Explain what prohibition and quarantine are.

How do insect pests damage crops?

Insect pests damage crops mainly by biting, chewing, boring and sucking.

• Biting and chewing: the pest eats leaves, fruits or seeds, as grasshoppers do.
• Boring: the pest tunnels into stems, fruits or grains, as stem borers and weevils do.
• Sucking: the pest draws sap from the plant, as aphids do.

Why are insect pests economically important?

Insect pests are economically important because they lower the income a farmer earns from crops.

1. Field damage: they destroy field crops by biting, chewing, boring and sucking.
2. Poor seed quality: they reduce the viability (germinating capacity) of stored produce.
3. Crop failure: heavy attack may lead to total crop failure.
4. Lower market value: damaged fruits and vegetables sell for less.
5. Higher cost: controlling insect pests increases the cost of production.
6. Disease spread: some insect pests act as vectors of plant diseases.
7. Lower yield and quality: they reduce the quantity and quality of crops, in the field or in store.

What are the methods of controlling insect pests?

There are six measures for preventing and controlling insect pests: cultural, physical, chemical, biological, prohibition and quarantine.

What is cultural control?

Cultural control is the use of good farm practices to reduce or destroy insect populations and to help crops escape attack.

• Crop rotation: growing different crops in turn on the same land breaks the life cycle of pests.
• Tillage: ploughing and harrowing expose eggs and pupae in the soil to the sun and to birds.
• Early planting: the crop grows and matures before the pest population builds up.
• Adequate and regular weeding: removing weeds takes away hiding places and alternative food for pests.
• Planting resistant varieties: these varieties are less easily damaged by insects.
• Timely harvesting: harvesting on time stops pests from attacking mature crops left in the field.
• Burning: burning crop remains destroys the eggs and larvae in them.

What is physical control?

Physical control is the removal or killing of insect pests by physical means, without chemicals.

• Hand picking: pests such as caterpillars are picked off plants and destroyed.
• Airtight storage: sealed containers cut off air, so insects in stored grain cannot survive or enter.
• Drying of produce: well-dried grains and seeds are less easily attacked in store.
• Trapping: traps catch insects so that they can be destroyed.

What is biological control?

Biological control is the introduction of natural enemies of an insect pest to feed on it and reduce its population.

• Example: ladybirds are introduced into an aphid-infested farm to eat the aphids.
• Advantage: it leaves no chemical residue on the crop.

What is chemical control?

Chemical control is the use of chemicals to protect crops from insect attack or to kill pests already present.

• Use: if an attack is already established, the chemicals kill the pests at various stages of their life cycles.
• Speed: it is widely used because it acts quickly on large attacks.

Insecticides

Insecticides are chemicals made specially for killing insect pests.

• Forms: they may be applied as solids such as dust, or as emulsions or sprays.
• Examples: Gammalin 20, Vector and Aldrin dust.

Fumigants

Fumigants are insecticides in the form of vapour or gas, used in enclosed spaces.

• Use: they are used in airtight containers or stores so that the vapour kills the insects.
• Examples: hydrogen cyanide, methyl bromide and ethylene oxide.

What is the difference between insecticides and fumigants?

What is prohibition?

Prohibition is a law that forbids the importing or movement of plants and produce that may carry insect pests.

• Aim: it stops dangerous pests from entering a country or spreading to a new area.

What is quarantine?

Quarantine is a period of isolation and observation imposed by law on imported materials such as seeds, plants and animals.

1. Imported materials are kept apart from local crops and animals.
2. They are observed long enough to show any disease symptoms.
3. If symptoms appear, the materials are destroyed or sent back to the country where they were bought.
4. The importer pays the cost.

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.