The word "pesticide" is a broad term that refers to any device, method, or chemical that kills plants or animals that compete for humanity's food supply or are otherwise undesirable. Pesticides include insecticides, fungicides, herbicides, nematocides (used to kill nematodes, elongated cylindrical worms), and rodenticides. Of these various pesticides, insecticides have a longer and more noteworthy history, perhaps because the number of insects labeled "pests" greatly exceeds the number of all other plant and animal "pests" combined. Hence, this article focuses on the use of agricultural insecticides.
Since they first began cultivating crops (around 7000 B.C.) if not before, humans have devised methods to prevent insects from eating or otherwise destroying precious crops. Some cultures relied on the practice of planting during certain phases of the moon. Other early agricultural practices that indirectly kept insect populations low were rotating crops; planting small, varied crops; and selecting naturally resistant plants. People picked bugs off plants by hand and made noise to ward off grasshoppers. Chemicals were also used early on. The crushed petals of the pyrethrum (a type of chrysanthemum), sulfur, and arsenic were used in the Middle East, Rome, and China, respectively. The Chinese also used natural predators such as ants to eat undesirable insects.
All attempts at pest control were pretty much individual affairs until the 1840s, when a North American fungus called powdery mildew invaded Britain, and the epidemic was controlled with large-scale applications of sulfur. The Colorado beetle in the western United States was the next target: by 1877 western settlers had learned to protect their potato crop by using water-insoluble chemicals such as paris green. Other pesticides such as derria, quassia, and tar oil followed, but nineteenth-century pesticides were weak. They had to be supplemented by introducing natural predators, or, in some cases, by grafting threatened plants onto more resistant rootstock.
By World War II, only about 30 pesticides existed. Research during the war yielded DDT (dichloro-diphenyl-trichloro-ethane), which had been synthesized in 1874 but wasn't recognized as an insecticide until 1942. Other strong pesticides soon followed, such as chlordane in 1945 and endrin in 1951. Poison gas research in Germany yielded the organophosphorus compounds, the best known of which is parathion. These new pesticides were very strong. Further research yielded hundreds of organophosphorus compounds, the most noteworthy being malathion, which was recently used in California against the medfly.
Until the 1800s, when people began to spray personal gardens using fairly large machines, pesticides were generally applied by hand. Airplanes were not used until the 1920s, and slow, well-controlled, low-level flights were not implemented until the 1950s. The first aerial spraying of synthetic pesticides used large amounts of inert materials, 4,000 liters per hectare (a hectare equals 2.47 acres). This quantity was rapidly reduced to 100 to 200 liters/hectare, and by the 1970s the amount had been reduced (in some cases) to.3 liters per hectare of the ingredient itself (for example, malathion) applied directly to the fields.
Today, some 900 active chemical pesticides are used to manufacture 40,000 commercial preparations. The Environmental Protection Agency (EPA) estimates that the use of pesticides doubled between 1960 and 1980. Currently, over 372 million kilograms a year are used in the United States, with over 1.8 billion kilograms a year used worldwide.
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