Q.What are pesticides and herbicides? Explain giving examples.

Both pesticides and herbicides are chemicals used in agriculture (and elsewhere) to control unwanted organisms, but they target different kinds of pests.

Pesticides are chemical substances used to kill or control organisms considered harmful to crops, stored grain, or human/animal health. They are a broad category that includes:

• Insecticides — kill insects, e.g. DDT (dichlorodiphenyltrichloroethane), which was widely used to control mosquitoes and agricultural pests (though now restricted in many countries due to its persistence and bioaccumulation in the food chain).
• Fungicides — kill fungi that cause plant diseases.
• Rodenticides — kill rodents such as rats.
• Nematocides — kill nematodes (parasitic worms) that damage plant roots.

Herbicides are chemicals specifically used to destroy unwanted plants, i.e. weeds, that compete with crop plants for nutrients, water and sunlight, without (ideally) harming the desired crop. Examples include:

• Sodium chlorate (NaClO3)
• Sodium arsenite (Na3AsO3)
• 2,4-Dichlorophenoxyacetic acid (2,4-D) …

Define pesticides broadly (with insecticide/fungicide sub-types and DDT as the classic example), then define herbicides specifically as weed-killers and name the …

• Treating 'pesticide' and 'herbicide' as synonyms — herbicide is a specific sub-type targeting weeds, while pesticide is the broader umbrella term (which also includes herbicides in the widest sense, but the …