What are pesticides and herbicides? Explain giving examples.

Explanation

Pesticides. These are synthetic toxic chemicals which are used in agriculture to control the damages caused by insects, rodents, weeds and various crop diseases. Their repeated use gives rise to pests that are resistant to that group of pesticides. As a result, these pesticides become ineffective for these pests.
Earlier DDT was used. As insect resistance towards DDT increased, other organic toxins such as Aldrin and Dieldrin were introduced for use as pesticides. But these were non-biodegradable and slowly transferred to human being through food chain causing metabolic and physiological disorders Consequently, a new series of pesticides, organophosphates and carbamates have been introduced These are biodegradable but are severe nerve toxins and hence more harmful to humans and have caused even deaths, Thus, the insecticide industry is engaged in developing new insecticides
Herbicides. These are the chemicals used to control weeds. Earlier, inorganic compounds such as sodium chlorate `(NaCIO_3)` and sodium arsenite `(Na_3AsO_3)` were used but arsenic compounds, being toxic to mammals, are no longer preferred. Instead, organic compounds such as triazines are now considered as better herbicides, especially for the corn-fields