Crop Plants: Pest Control

Pests such as insects and other animals can damage crops by eating them
Weeds can outcompete crop plants for space, water and soil nutrients
Fungi can infect crop plants and spread disease which can affect growth and yield
All of these can be controlled by using pesticides (chemical control) or by introducing other species (biological control)
Examples of pesticides include:
- Insecticides kill insect pests
- Herbicides kill plant pests
- Fungicides kill fungal pests

Advantages	Disadvantages
Easily accessible and relatively cheap	Organisms they are meant to kill can develop resistance to them
Have an immediate effect	They are non-specific chemicals and can often kill other beneficial organisms (e.g., some insecticides might kill bees, which are important pollinators of crops)
Kills the entire population of pests	They can be persistent chemicals – this means they do not break down in the body and can accumulate in great concentrations at the top of food chains and harm top predators (known as bioaccumulation)
	Need to be repeatedly applied

Biological control involves using a natural predator to eat the pest species and therefore reduce the impact of the pest on crop yields
This can happen naturally – for example, ladybirds eat aphids
Usually, a species is introduced specifically to prey on the pest species – for example, parasitic wasps can control whitefly in glasshouse tomato crops
As they are based on a predator-prey cycle, they do not completely remove a pest, but keep it at lower levels

Advantages	Disadvantages
Natural method - no pollution	May eat other organisms instead of the pest
No resistance	Takes a longer period of time to be effective
Can target specific species	Cannot kill entire population - some pests will always be present
Long lasting	May not adapt to new environment or may move out of the area
Does not need to be repeatedly applied	May become a pest itself

Crop Plants: Pest Control (Edexcel IGCSE Biology: Double Science)