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Pesticides–What Are They?

This article was originally published on April 5, 2010 and expired on May 15, 2010. It is provided here for archival purposes and may contain dated information.

Pesticides are used every day, but many people are not aware of their properties and uses. A pesticide is any chemical that is used to kill, repel or control a pest. It is important to remember that a pesticide may not always "kill" the pest, but the pesticide controls the pest.

Pest, in this definition, refers to animals, weeds or microorganisms that compete with a resource desired or needed by man. Gardeners usually view pesticides as controlling insects, weeds or diseases.

The term pesticide covers many types of chemicals that are known by specific name depending on the type of pest it controls. For instance, insecticides are chemicals used to control insects and other related animals like mites. In a similar manner herbicides control weeds; fungicides control fungi; bactericides control bacteria; rodenticides control rats, mice and other rodents; avicides control birds and molluscides control slugs and snails.

Pesticides affect the target organisms in several ways. Many interfere with vital life processes, causing death. The insecticide Malathion affects the insect's nervous system. The rodenticide warfarin prevents blood clotting in rats leading to internal hemorrhaging.

Attractants are also a type of pesticide. Pheromones include insect hormones that attract insects. These are used in luring insects into a trap, luring them away from susceptible plants or confusing them so much that they do not feed or mate.

Repellents keep pests from infesting certain areas or from tormenting humans. Think about the products you apply to your skin and clothing to avoid mosquitoes.


Plant growth regulators change the normal growth or reproduction of a plant. The herbicide 2,4-D speeds up the growth of plants in small concentrations, but plants grow abnormally or die when exposed to higher concentrations.

Paraquat, an example of a harvest-aid, causes leaf drop in cotton so that the plant dries and can be harvested more efficiently.

Pesticides are a wide and diverse group of chemicals. These chemicals are an aid to our way of life, but they are closely regulated by the Environmental Protection Agency and Department of Agriculture so that they are used properly and safely.

All pesticides should be applied according to the directions on their label. Failure to follow labeled instructions is a violation of the federal law.

Source: David J. Robson, Extension Specialist, PSEP, drobson@illinois.edu

Pull date: May 15, 2010

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