In past centuries pests, such as apple woolly aphid, were sprayed with natural products, such as turpentine and soap, while weeds were removed by hand. In the nineteenth century, the chance development of Bordeaux mixture from inorganic copper sulphate and slaked lime, and in the early twentieth century the expansion of the organic chemical industry, enabled a change of emphasis in crop protection from cultural to chemical control.
The word 'pesticide' is used in this book to cover all crop protection chemicals, which include herbicides (for weeds), insecticides (for insects), acaricides (for mites), nematicides (for nematodes) and fungicides (for fungi). About 2.5 million tonnes of crop protection chemicals are used worldwide each year, about 40 per cent being herbicides, about 40 per cent insecticides and about 20 per cent fungicides. Health and Safety aspects of chemical control are described at the end of the 'chemical control' section.
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