Tomato plant with red mite. Image credit

Tomato plant with red mite. Image credit

ZIMSEC O Level Combined Notes: Pest Control

  • Pests cause damage to plants and spread diseases.
  • This results in a reduction in crop yields.
  • Control measures can be taken to minimise this damage.
  • The control measures can be either chemical or natural/cultural.

Chemical method of pest control

  • Chemicals can be used to minimise the damage done to crops by pests.
  • A pesticide is any substance that kills pests.
  • Some plant diseases however a caused by fungi.
  • A chemical that is used to kill fungi is known as a fungicide.
  • Chemicals used in pest control include Copper Oxychloride, DDT ( although it has been banned for a while now in most countries including Zimbabwe) Roger CE, Karate, Kelthane HF, Dimethoate 40 EC.

Cultural methods

  • these are methods of pest and disease control that to not make use of chemicals.
  • They are more long term in nature i.e. they take a long time to be effective in most instances.
  • Methods includes the fumigation of seedbeds e.g. tobacco seedbeds using wood smoke to kill.
  • The growing maize and tobacco plants can also be sprayed with a solution of milk and water thus reducing the infection of plants by diseases.
  • Crop rotation and hand picking of pests are also practiced.
1. Quick
2. Specifi (only affects one pest)
3. Can be controlled when used correctily
1. Expensive
2. Kill or damage other animals.
3. May stay in the soil or water for long periods of time affecting other animals in the food chain for example DDT
4. Higher and Higher doses of chemicals are needed as pests become resistant to chemicals.
1. Low cost
2.Easily accessible natural resources e.g. milk and ash
3. Are safe as they are part of the natural enviroment
1. Their effect takes time to be felt (Are slow acting).
2. Need to be frequently carried out and applied e.g. Crop rotation

Pest control in Zimbabwe

  • The American bollworm can destroy cotton crop if it is not controlled.
  • The bollworm moth lays eggs in the buds and flowers of the cotton plant.
  • The eggs hatch into the bollworms which feed and grow in the cotton plant.
  • The pest can be controlled without chemicals at each stage of the life cycle from eggs through to adult moths.
Stage in Life cycleControl
eggs-spread fine wood ash over the plants
Bollworms (caterpillars)-spray with liquid soap solution.
-hand-pick from plants.
-Hens and bantams eat the caterpillars.
-Use of insecticidal spray made from plants like tobacco and pyrethrum
pupae on the ground-hens eat pupae
-plant extract sprays.
adult moths-spray with extracts from plants with a strong smell like khaki wee, eucalyptus leaves or herbs.
-light traps
  • As already explained above wood smoke fumigation and milk and water solutions can be used to control pests in maize and tobacco.
  • In addition chemicals can be used during the fumigation stage.
  • Nematode worms in the soil attack tobacco plants and there are few cultural methods that can be used to control these worms.
  • Farming practices such as isolating the infected plants, importing predators to feed on the pests and practising crop rotation can be used.
  • Crop rotation is part of the permaculture approach to farming where crops and other plants are raised in mixed farming.
  • The variety of crops reduces the spread of diseases.
  • The use of chemicals should be avoided wherever possible as pests tend to get resistant with exposure, trace amounts remain and may accumulate and cause harm in the food chain and they are expensive.

To access more topics go to the Combined Science Notes page.