Nature and use of pesticides P esticides, as the active ingredients in pest control products, are designed to mitigate or prevent the injurious, noxious or troublesome effects of pests on human life. Pests include weeds, pathogens and insects. There are an estimated 50,000 types of weeds in the world, far more than the 400 or so plant species that we cultivate as crops. Some weeds produce as many as 10,000 seeds/m and, even with only a 1% emergence rate, compete strongly for water and nutrients with any crop a farmer intends to grow. Hence, pesticides are important control agents in food production and security. Pesticides are also important agents in protecting human populations from disease. one pesticide that has saved millions of lives is dichlorodiphenyltrichloroethane (DDT). This insecticide has historically been so successful in providing mosquito control, including Anopheles spp. which transmits malaria, that some scientists believe DDT has in fact saved more human lives that any other chemical we know, including penicillin. Since the 1940s, the worldwide use of pesticides in agriculture has increased by an average of 11% per year. The quantity of pesticides used worldwide is now estimated to be at least 3 billion kg. In 2006, approximately 36 million kg of pesticides were used in crop production in Canada. The quantity used in each province generally reflects the area of the cropland. Saskatchewan, with the largest area at 17.9 million ha, received about 17.4 million kg of pesticides in 2006, almost half of the total quantity used in Canada. The use in Alberta was about 8.4 million kg on 10.6 million ha of land and in Manitoba, about 4.6 million kg on 5.0 million ha. Thus, in 2006, the Canadian prairies received about 84% of the total mass of pesticides applied in Canada. Pesticide use on cropland in Canada from 1981 to 2006 was relatively constant, ranging from 29.7 million kg/y to 35.4 million kg/y. Benefits and hazards of pesticide use The current reliance of North American agriculture on pesticide use is not without controversy. Pimental estimates that every dollar invested in pesticide control in the united States saves $4 dollars in crops but also costs about $1 dollar for damages to environmental and public health. This estimate is significant because the investment in pesticide control in the united States is about $10 billion annually, thus yielding $40 billion dollars in food security benefits but also $10 billion dollars in environmental and public health risks.
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