Pesticides

A pesticide is any substance or mixture of substances intended for preventing or destroying any pest. There are a number of different pesticides, each meant to be effective against a specific pest.

Pesticides include herbicides for destroying weeds and other unwanted vegetation, insecticides for controlling a wide variety of insects, fungicides used to prevent the growth of molds, disinfectants for preventing the spread of bacteria and sanitizers.

Pesticide products contain both active and inert ingredients. An active ingredient prevents, destroys, and repels a pest.  All other ingredients that are important for product performance and usability are called inert ingredients.

Classification of Pesticides

There are three most popular ways of classifying pesticides. They are, based on the mode of action, based on the targeted pest species and based on the chemical composition of the pesticide.

Classification of pesticides based on the mode of action

In this classification, pesticides are classified as non systemic and systemic pesticides.
The non-systematic pesticides do not penetrate the plant tissues and only have an effect when they come in contact with the targeted pest.
Examples of contact pesticides are paraquat and diquat dibromide.
The systemic pesticides are those which effectively penetrate the plant tissues and move through the plant vascular system in order to bring about the desired effect.
Examples of systemic pesticides include 2, 4-D and glyphosate

Classification of pesticides based on the targeted pest species

In this type of classification, pesticides are named after the name of the corresponding pest.
Examples are insecticides and fungicides which target insects and fungi respectively.

Classification of pesticides based on the chemical composition

Based on chemical classification, pesticides are further classified into four main groups:  Organochlorines, Organophosphorous, Carbamates and Pyrethrin and Pyrethroids
This is the most useful classification of the three because it gives an idea about the physical and chemical properties of the pesticides, the knowledge of which is very important in the mode of application, precautions that are to be taken and the application quantities estimation.

Organochlorines pesticides are mainly used as insecticides to control a wide variety of insects. They act as nervous system disruptors leading to convulsions and paralysis of the insect and its eventual death.
Some of the commonly used organochlorine pesticides are DDT, lindane, endosulfan, aldrin, dieldrin and chlordane.

Organophosphorous pesticides are also insecticides that are generally more toxic causing a rapid twitching of voluntary muscles causing paralysis and death.
Some of the widely used organophosphorous insecticides include parathion, malathion, diaznon and glyphosate.

Carbamates are organic insecticides that are derived from carbamic acid. Some of the widely used insecticides under this group include, carbofuran, aminocarb and carbaryl.

Pyrethroids are synthetic counterparts of the naturally occurring product of pyrethrum plant flowers, pyrethrins. These are widely used for their instant effect on insect pests, low mammalian toxicity and facile biodegradation.
The most widely used synthetic pyrethroids include permethrin, cypermethrin and deltamethrin.

Fungicides are pesticides that are used for the control of fungal infections in crops. There are inorganic and organic fungicides.
Inorganic fungicides include Bordeaux mixture, Cu(OH)2.CaSO4 and malachite, Cu(HO)2.CuCO3.
Organic fungicides on the other hand include among others, benomyl and oxine copper.

Biodegradation is the breakdown or transformation of pesticides by microbial agents which normally occurs in water and soil. The rate of microbial degradation depends highly on the amount and nature of pesticides present in the soil, the microbial population in the soil and soil conditions.

Pyrethroids, organophosphates and some carbamates are more susceptible to biodegradation. However, most organochlorines are resistant to biodegradation due to the strength of C-Cl bond present in their active compounds.
The removal of redundant pesticides from soil is very important as they can prove to be dangerous in most cases. Consumption of pesticides of any kind can cause health problems in human beings.

Advantages of pesticides

Pesticides are used for controlling pests which results in improved crop yield and quality.
Pesticides are helpful in controlling the populations of mosquitoes that can cause major diseases such as dengue and malaria.
Herbicides help in controlling the growth of weeds that compete with the main crop with space and water.
Disinfectants and sanitizers help maintain healthy and hygiene conditions inhibiting the growth of harmful bacteria.

Disadvantages of pesticides

Pesticides are proven to be harmful to humans when used in uncontrolled amounts and can cause various health problems ranging from simple irritation in the eyes to more severe effects such as affecting the nervous system.
Organophosphate insecticide exposure is found to cause neurobehavioral alterations.
Pesticide use also has serious environmental effects. A major part of the sprayed pesticides don't reach the target but a destination other than the target, including air, water and soil. This causes pollution in the environment.
The chemicals in some older pesticides can remain for years in soil and water thus polluting them. They are still used in many developing countries as pesticides.