text: From biblical times until the 1950s the pesticides used were inorganic compounds and plant extracts. The inorganic compounds were derivatives of copper, arsenic, mercury, sulfur, among others, and the plant extracts contained pyrethrum, nicotine, and rotenone among others. The less toxic of these are still in use in organic farming. In the 1940s the insecticide DDT, and the herbicide 2,4-D, were introduced. These synthetic organic (i.e. non inorganic) compounds were widely used and were very profitable. They were followed in the 1950s and 1960s by numerous other synthetic pesticides, which led to the growth of the pesticide industry. During this period, it became increasing evident that DDT, which had been sprayed widely in the environment to combat the vector, had accumulated in the food chain, and become a global pollutant, as summarised in the well-known book Silent Spring. Finally, DDT was banned in the 1970s in several countries, and subsequently all persistent pesticides were banned worldwide, an exception being spraying on interior walls for vector control.
  Resistance to a pesticide was first seen in the 1920s with inorganic pesticides, and later it was found that development of resistance is to be expected, and measures to delay it are important. Integrated pest management (IPM) was introduced in the 1950s. By careful analysis and spraying only when an economical or biological threshold of crop damage is reached, pesticide application is reduced. This became in the 2020s the official policy of international organisations, industry, and many governments. With the introduction of high yielding varieties in the 1960s in the green revolution, more pesticides were used. Since the 1980s genetically modified crops were introduced, which resulted in lower amounts of insecticides used on them. Organic agriculture, which uses only non-synthetic pesticides, has grown and in 2020 represents about 1.5 per cent of the world’s total agricultural land.
  Pesticides have become more effective. Application rates fell from 1,000–2,500 grams of active ingredient per hectare (g/ha) in the 1950s to 40–100 g/ha in the 2000s. Despite this, amounts used have increased. In high income countries over 20 years between the 1990s and 2010s amounts used increased 20%, while in the low income countries amounts increased 1623%.