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An airplane spreading pesticide.
An airplane spreading pesticide.

A pesticide is a chemical, or sometimes biological agent such as a virus or bacteria, used to control, to repel, to attract, or to kill pests, which are organisms, including insects, weeds, birds, mammals, fish, and microbes, that compete with humans for food, destroy property, spread disease, or are considered a nuisance. Pesticides are usually, but not always, poisonous to humans.


Pesticides active against higher level animal life forms

Repellents and attractants

Pesticides active against plants and lower level life forms

It is important to note that using chemical pesticides to eliminate insects works against the over-all goal of eliminating the targeted pest. The natural equilibrium that is maintained between predator/prey relationships swing to an unnatural state. Prey tends to reproduce quickly whereas predator insects have a lag in growth rate dependent on the availability of their food source. After pesticides are employed relatively all insects are killed. The target insect, usually the plant consumer, will return to the system first. There will be significant lag time before its predator returns to the system. Therefore, the returning consumer will have uncontrolled opportunity to feed and breed. Pests may be found in greater numbers weeks after the pesticide use than before. This necessitates the constant cycle of pesticides.


Since before 500 BC humans have used pesticides to prevent damage to their crops. The first known pesticide was sulfur. By the 15th century, toxic chemicals such as arsenic, mercury, and lead were being applied to crops to kill pests. In the 17th century, nicotine sulfate was extracted from tobacco leaves for use as an insecticide. The 19th century saw the introduction of two more natural pesticides, pyrethrum, which came from crysanthemums, and rotenone, from the roots of tropical legumes.

In 1939, Paul Müller discovered that DDT was a very effective insecticide. It quickly became the most widely used pesticide in the world. However, in the 1960s, it was discovered that DDT was preventing many fish-eating birds from reproducing, which was a huge threat to biodiversity. DDT was also found to cause birth defects in animals and humans. DDT is now banned in at least 86 countries, but is still used in some developing nations to prevent malaria and other tropical diseases by killing mosquitos and other disease-carrying insects.

Pesticide use has increased 50-fold since 1950, and 2.5 million tons of industrial pesticides are now used each year. The most widely used pesticides today are nonpersistent organophosphates, including glyphosate (the active ingredient in Roundup), which is currently the world's most used herbicide.


In the US, all materials intended for sale and use as pesticides must be registered with the EPA. The process may be long, complex, and expensive, because research must prove that the material is effective against the intended pest, yet safe to use. During the registration process a pesticide label is created, which has directions for proper use of the material. Use inconsistent with the label is pesticide misuse.

Preparing for the spread of pesticides.
Preparing for the spread of pesticides.

Some pesticides are considered too hazardous for sale to the general public, and these are designated restricted use pesticides. Only certified applicators, who have taken a course and passed an examination, may purchase or apply restricted use pesticides. Records of sales and use are kept, and can be audited by the EPA.

"Read and follow label directions." is often quoted by extension agents, garden columnists and others teaching about pesticides. This is not merely good advice; it is the law, for the USA. Similar laws exist in much of the rest of the world. The Federal Insecticide, Fungicide, and Rodenticide Act of 1972 (FIFRA) set up the current system of pesticide regulations. It was amended somewhat by the Food Quality Protection Act of 1996. Its purpose is to make pesticide manufacture, distribution and use as safe as possible. The most important point for users to understand is that it a violation to apply any pesticide in a manner not in accordance with the label for that pesticide. It is a crime to do so intentionally.

Dangers of Pesticides

There are claims that pesticides present some danger to humans when used to control weeds or insects on food crops. This is one basis for the organic food movement. All food crops including many fruits and vegetables such as apples, peppers, celery, cherries, grapes, nectarines, peaches, pears, potatoes, red raspberries, spinach, and strawberries contain residual pesticides after being washed or peeled. These residues, permitted by (US) government safety standards, are regulated under set tolerance levels and are considered safe based on average daily consumption of these foods by adults and children. These consumption levels are based on scientifically sound risk assessment models that require pesticide manufacturers to produce extensive toxicological and residue research data in order to test pesticides prior to their registration for use on a particular food crop in the US.

Besides human health risks, pesticides also pose dangers to the environment. Non-target organisms can be severely impacted. In some cases where a pest insect normally has some controls from a beneficial insect predator or parasite, an insecticide application can kill both pest and beneficial. The control insect almost always takes longer to recover than the pest. Applications for adult mosquitoes, for example, may temporarily depress mosquito populations, but cause a larger population in the long run, by damaging controlling factors.

One of the earliest discovered problems in pesticide use was that pests can and do eventually evolve to become resistant to the chemicals. When sprayed with chemicals, most pests will be entirely susceptible. However, not all pests are killed; some with slight variations in their genetic make-up are resistant and therefore survive. Natural selection will ensure that the organisms with resistant genetic make-up survive, and eventually the pests will become entirely resistant to the pesticide. Unaware of how to deal with this problem, farmers often increase their use of pesticides, causing further problems. When resistance is not a problem, pesticides in general are highly effective for controlling pests if the other disadvantages are taken into account.

Another less known trouble the environment faces as a result of pesticides are known as ‘'persistent organic pollutants’' (POPs). POPs continue to poison non-target organisms in the environment and possibly increase chances to humans of disruption in the endocrine system, cancer, infertility, and mutagenic effects, although very little is known about these ‘long-term chronic effects’ yet.

Misuse of pesticides can cause pollinator decline, which is a food supply issue.

Continuing Development of Pesticides

Pesticides are tools of convenience and are highly efficient for producers who are in the business of mass food production. Pesticide safety education and pesticide applicator regulation are designed to protect the public from pesticide misuse, but do not eliminate all misuse. Reducing the use of pesticides and replacing high risk pesticides is the ultimate solution to reducing risks placed on our society from pesticide use. For over 30 years, there has been a trend in the United States and in many other parts of the world to use pesticides in combination with alternative pest controls. This use of integrated pest management (IPM) is now commonplace in US agriculture. With pesticide regulations that now put a higher priority on reducing the risks of pesticides in our food supply and emphasize environmental protection, old pesticides are being phased out in favor of new reduced risk pesticides. Many of these reduced risk pesticides include biological and botanical deriviatives and alternatives. As a result, old, more hazardous, pesticides are being phased out and replaced with pest controls that reduce these health and environmental risks. Chemical engineers continually develop new pesticides to produce enhancements over previous generations of products. In addition, applicators are being encouraged to consider alternative controls and adopt methods that reduce the use of chemical pesticides. This process is on-going and will not solve all of our problems of pesticide use risks overnight.

Pesticide use maps in the US

The US Geological Survey's National Water-Quality Assessment Program published a 1997 Pesticide Use Maps which shows estimates of pesticide type and intensity of pesticide use by County (United States).

See also



  • Greene, Stanley A.; Pohanish, Richard P. (editors) (2005) Sittig's Handbook of Pesticides and Agricultural Chemicals, SciTech Publishing, Inc. ISBN 0815515162
  • Hamilton, Denis; Crossley, Stephen (editors) (2004) Pesticide residues in food and drinking water, J. Wiley. ISBN 0471489913
  • Hond, Frank (2003) Pesticides: problems, improvements, alternatives, Blackwell Science. ISBN 0632056592
  • Kegley, Susan E.; Wise, Laura J. (1998) Pesticides in fruits and vegetables, University Science Books. ISBN 0935702466
  • Miller, G. Tyler Jr. (2002). Living in the Environment (12th Ed.). Belmont: Wadsworth/Thomson Learning. ISBN 0-534-37697-5
  • Ware, George W.; Whitacre, David M. (2004) Pesticide Book, Meister Publishing Co. ISBN 1892829118
  • Watson, David H. (editor) (2004) Pesticide, veterinary and other residues in food, Woodhead Publishing. ISBN 1855737345

Journal Articles

  • Walter A. Alarcon, (July 2005). Acute Illnesses Associated With Pesticide Exposure at Schools, Journal of the American Medical Association, 294: 455–465

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