Pest and Disease Management
Growers want to control pests and diseases to get maximum production and prevent crop loss. Prevention of pests and diseases before any damage is done is most desirable.
Four common methods of control of pests and diseases are biological, cultural, chemical, and integrated control.
Biological control
This uses useful living organisms, such as predators or parasites, to control pests.
Predator insects feed on the pests and can control their numbers. There are some parasites that live part of their life inside plant pests and finally kill them.
Biological control can occur naturally or growers can release predators and parasites deliberately.
Here are examples of natural biological control.
Ladybirds prey on aphids. Spiders prey on most insects including pests. Birds prey on grass grubs and other pest larvae. Thrushes feed on snails.
White butterfly.Scientists study pests, their life cycles and history. Then they examine the natural predators or parasites of the pest.
This type of research was used to find a biological control for white butterfly.
It has been effectively controlled by its natural predators.
Apanteles wasp attacks white butterfly larvae. Pteromalus wasp attacks white butterfly pupae.
White butterfly caterpillar, pupa and adult.Pteromalus and Apantales are both tiny wasps. Apantales is a wasp that is only three millimetres long. When it lays its eggs on the white butterfly caterpillar, they hatch into larvae and kill the caterpillar. The Pteromalus wasp attacks the next part of the white butterfly lifecycle, the pupa. When its eggs hatch on the white butterfly pupa, its larvae feed on and destroy the pupa. Neither of these wasps occurs naturally in New Zealand. Scientists brought them in from overseas and bred them. They were then released in areas where the white butterfly is a pest.
Open HT1103A [PDF 643kB] and look at photos 23–25 to see some other examples of biological control.
Advantages and disadvantages of biological control
Biological control methods do not involve chemicals, so they leave useful insects unharmed. They only target the pest affected. Once established biological control is cheap, cost-free and does not harm the environment.
Biological control is costly to develop and manage. It takes time to work and usually the pest populations are high before there are significant numbers of predators and parasites.
Key points
- Four common methods are used to control pests and diseases. They are: biological, cultural, chemical and integrated control.
- Biological control is the use of useful and beneficial living organisms, such as predators or parasites, to control pests.
- Predator insects feed on the pests and can control their numbers.
- There are some parasites that live part of their life inside plant pests and finally kill them.
- The advantage of biological control is it is cheap in the long term and does not harm the environment and useful insects. The disadvantage of biological control is that it takes time to work and usually the pest populations are high before significant numbers of their predators or parasites are present. It is also costly to develop and manage.
What's next?
Go to: 5 Cultural control.