5.4 Pesticide and Biological Control

5.4 Pesticides and Biological Control 

Understand the reasons for pest control and the advantages and disadvantages of using pesticides and biological control with drop plants

Where we have large field of crop all with the same type (monoculture), they tend to be very susceptible to pests, which use crop as their food sources.

This will reduce the productivity of farming ---> loss of food & financial impact 

To overcome this farmers can use…

1. Pesticides - chemicals designed to kill the pests

Advantages

- Chemicals = easy to obtain

- Easy to apply 

- Very effective

Disadvantages

- Toxic = killing other plants and animals other than the pests, and may be harmful to humans

- Bioaccumulation = pesticides buildup through the food chain causing problems for animals in the higher trophic level. Eg DDT

- Mutation in the pests often leads to resistance = pesticides have to be applied in higher concentration --> more toxic/ no longer work --> we have to find alternative pesticides 

2. Biological Control

For example..

In Australia, Cactus A of North America was introduced to gardens, and escaped into the country side and flourishes under Australian climate and ecosystem. The cactus then starts to cover a good deal of agricultural land and it was necessary to get rid of this. 

However, there were no natural predators of such cactus in Australia, so it was necessary to introduce alien species from another country, which was a moth/larvae, which feeds on the cactus (Cactoblastis). It has no competitors and was able to eat away this cactus and remove it from the agriculture land of Australia.

This control of pests by herbivore is called biological control. 

Advantages:

- No toxic/ chemicals involved

- Less impact on man and wildlife

Disadvantages: 

- Not 100% effective

- Difficult to control = always a danger that introduced species will find alternative prey on which to feed and will not actually die out once the pest has been removed

- Difficult to math a predator to the prey (to remove your pest)