Introduction to basic chemicals applied in the field of agriculture.

1. Agrochemicals
Chemical product used in agriculture, to protect
crops from pests, weeds and enhance crop yields

2. Crop protection chemicals can be broadly classified as
 (1) insecticides,
(2) fungicides,
 (3) herbicides,
(4) pesticides and
 (5) rodenticides.
 The per capita consumption of crop protection products
 India (0.6 kg / hectare)
 USA (7 kg / hectare).

3. Properties of Ideal pesticides
 (a) It should have a broad spectrum to kill the pests.
 (b) They should not toxic to other animals and plants.
 (c) They should not increase in concentration with each level of the
food chain.
 (d) They should not permanently stored in the body tissue.
 (e) They should not disrupt the balance of an ecosystem,
 (f) They should not cause birth defects.
 (g) They should have low production cost.
 (h) They should be easily formulated.

4. Pesticides:
 Chemicals in general are used for
 preventing,
 destroying,
 attracting,
 repelling or
 controlling
 any pest including unwanted species of plants or animals

5. Insecticides:
 Insecticides are the chemicals that protect the crops from the
insects by killing them, preventing their attack, repelling the
insects and killing mitigate insects (belonging to class insects,
Phylum Arthropoda).
Insecticides are classified on the basis of
a. Chemical nature
b) mode of entry
c) mode of action.

6. Classification based on the chemical nature:
 (i ) Inorganic compounds : arsenicals, fluorine compounds.
 (ii) Organic compounds: DDT, HCH, phenyl derivatives,
carbamates etc.
 (iii) Botanicals: nicotine, rotenone, pyrethrum etc.

7.  The systemic insecticides should be water soluble and
to enable the compounds to move in the plant.
 They should penetrate into the plant through roots, stems
and leaves.
 Examples: Chlorinated hydrocarbons like DDT (1,1,1-
trichloro-2,2 bis(p-chlorophenyl)ethane) is proved to be
extremely effective against flies and mosquitoes.
 But, DDT has environmental hazard due to its long
residential life and to its accumulation.

8. Organophosphates
 Organophosphates like, methyl parathion (0,0-
dimethyoxy-p-nitrophenyl phosphorothioate) is lower
toxicity to humans and domestic animals.
 Other examples are malathion, carbamates,
carbofurans.

9. Pyrethroid:
 Pyrethroid: first generation: pyrethrin-I, allethrin
 second generation: tetramethrin
 third generation: fenvalerate.
 Pyrethrin's are highly potent against insects and lower
toxicity to human beings and animals.

10. Classification Based on mode of entry:
 1. Stomach insecticides: The insecticides eaten by the insects
are known as stomach insecticides.
 These insecticides are active against the chewing insects such
as caterpillars, grasshoppers, etc.
 Their application is through food and entry through the midgut of
the insect. Example: DDT, HCH,

11. Classification Based on mode of entry:
2.Contact insecticides:
 These insecticides kill the insects due to external contact
and absorption through skin.
 Their application is through the body surface and entry
through the cuticle and tracheae.
Example: pyrethrum, rotenone, toxaphene.

12. Classification Based on mode of entry:
3.Fumigants:
These exert their action in the gaseous state to kill
the insects.
These substances act on the insects through the respiratory
system as their vapors enter through the tracheae.
Example: HCN, methyl bromide, DDVp

13. classification Based on mode of action:
 (i) Physical poisons (which kill the insects by suffocation).
 (ii) Inert dusts (which effect a loss of body moisture from insects).
 (iii) Heavy mineral oils (which exert a purely asphyxiant effect).
 (iv) Respiratory poisons (which combine with cytochrome oxidase and
inhibit their catalytic action).
 (v) Nerve poisons (which is associated primarily with solubility of the
tissue lipids).