 |
The following section gives a brief history of how pests were controlled in the past. It also discusses how some of these methods involving chemicals were dangerous and caused much concern. Pre-industrial Agriculture has a history of about 10,000 years. Pest control in pre-industrial times was acheived mostly by cultural methods. Weeds were ploughed and grazed and plants were chosen for their ability to outcompete weeds.  Herbal remedies were used for animal diseases.  Animal
pests were controlled by occassional culling or poisoning.  Farmers
observed and encouraged mutual relationships between different species.
For example, In China, ants were used to control sucking insects on
citrus plants. Some plants were seen to grow better in the presence
of other plants. This is called companion planting. There were isolated examples of chemical control. For example, the Romans used sulphur to destroy insect pests on their crops. Pest control was often not very effective in comparison to the level achieved in modern times and so yields were much lower. Emergence of Chemicals 
Prior to the second world War chemical plant protection depended on
a few inorganic substances - commonly compounds of arsenic, copper or sulphur - complemented by a few naturally occurring organic chemicals such as nicotine and pyrethrins, used as insecticides. Many organic compounds were developed during the second world war for military use. After the war, good economic conditions permitted the rapid development of the chemical industry. Thus, although we regard chemical protection as the norm, it has a brief history in the agricultural time scale. 
After the Second World War, the development of DDT and other organochlorines
opened up a whole new era in pest control. Pest control was cheap
and effective and seen as relatively safe. The use of chemicals as a pest control measure has increased dramatically since the advent of DDT so that by 1990, the production of organic chemicals had increased to over 250 million tonnes per year worth over $15 billion. Today, nearly all food products contain pesticide residues. They are applied before and during the growing period and after the crops are harvested or animals are slaughted, when food is treated with pesticides during storage. Backlash to Chemical Use In 1962, Rachel Carson wrote a book called "Silent Spring" in which she highlighted the dangers of organochlorines such as DDT and the impact that these types of chemicals were having on the environment in general. Organochlorines are very stable in the environment and take a long time to break down. This means that they remain toxic in the environment for some time, killing non-target organisms. The outcry over the effects of organochlorines, highlighted in Carson's book, resulted in governments, scientists and farmers looking for alternative methods of pest control, and stricter criteria on the use of chemicals for pest control. Although the chemicals used today are much less persistent and so pose a significantly reduced risk to the environment, there is still a large proportion of the population who are concerned about chemical residues in food. In 1990 a survey found that 50% of food samples contained pesticide residues, the majority within the legal limit allowed (How Green is My Trolley). This issue is discussed further in the section on chemicals Developing Alternatives to Chemical Use With an increased concern that chemicals were being misused or overused in the control of pests, scientists increased their efforts to look for alternatives. You can learn about what they have acheived in the sections on: Biocontrol Genetic IPM |
|
|