Why Do We Need Pesticides

Food crops are subject to attack by a multitude of pests and diseases and pesticides are applied to minimize the damage to the crop. It has been estimated that without protection world cereal crop yields would fall by between 46 and 83%. History is littered with records of crop failures and famine caused primarily by rodent, insect or fungus. Some of these events have had a wide-ranging and long-lasting effect, like the 1845-1846 Irish potato famine and the 1917-1918 German 'turnip winter,' the latter so called because the potatoes rotted and turnips were the only stored root crop that was available to feed the population through the winter. Both these events, in which 1.5 million and 700 000 people died, respectively, were caused by potato blight, infection by the fungus Phytophthora infestans. Famine caused by massive swarms of locust is still all too common in Northern Africa and Arabia. Less spectacular but as disastrous is the loss of an estimated 30% of harvested crops in India to rodents.

In addition to the loss of the crop, pesticides are used to control agents which make the crop toxic rather than healthy. Two examples are the toxins caused by fungi. When an insect bores into a peanut it allows spores of the fungus Aspergillus flavus to enter and grow, producing the aflatoxins, a series of carcinogens. When rye (Secale cereale) grows in damp conditions a fungus, Claviceps purpurea, can grow on the seed. If this seed is subsequently ground into flour and made into bread it can cause consumers to suffer hallucinations, gangrene, and death. Outbreaks amounting to epidemics were common in the Middle Ages in Europe and one occurred as recently as 1951 in France.

A second reason relates not so much to quantity as to quality. Supermarkets in the developed nations offer a wide range of fresh produce at competitive prices. Consumers do not like holes made by slugs and snails in their fresh lettuce. They do not expect scab marks on their apples, or holes made by small maggots in their carrots. Flour millers do not expect to have to clean the grain from weed seeds before milling. Even small defects can dramatically reduce the value of the crop, or indeed make it unsaleable, and the need for a competitive price requires minimal labor input so that application of pesticide is essential.

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