Insecticides

A crop standing in the field is never fully safe. Different harmful insects eat the plants or spread disease among them, and the harvest falls. Larvae that chew vegetable leaves, weevils that breed in stored grain and insects that attack fruit are all enemies of this kind. To kill or control them, farmers use different insect killing substances.

An insecticide is applied either as a dust sprinkled over the plant or as a liquid sprayed on it. Malathion, for example, is sprayed to destroy the insects that attack vegetable crops and fruit.

Insecticides are classified into two kinds, bio insecticides and chemical insecticides. A bio insecticide can be made at home from local plants, while a chemical insecticide is manufactured in industry from chemicals.

Jholmol, a liquid brewed from strong smelling plants, is one example of a bio-insecticide. The ash that village farmers dust over their vegetable beds is another. Placing asuro, the Malabar nut plant, in the soil before planting potatoes, keeping neem leaves in grain stores, and killing bedbugs with a liquid of titepati, which is mugwort, and neem are all everyday uses of bio-insecticides.

Careless use of chemical insecticides pollutes both the physical and the living environment. Bio-insecticides can be used in their place. A bio-insecticide helps drive insects away from plants and protects the plants from disease. It does not harm the soil or other living things, and it does not harm human health either.

DDT, whose full name is dichloro diphenyl trichloroethane, BHC, which is benzene hexa chloride, methoxy chloride, aldrin and dialdrin are all chemical insecticides. Malathion, sprayed on vegetables and fruit, belongs to this same group.

An insecticide destroys the insects that attack a crop, so the harvest grows larger. Yet even while protecting the crop, these substances create many harmful effects in the environment. That is why a farmer uses a chemical insecticide out of compulsion, not out of choice. Such chemicals are a kind of poison.

When the residues of an insecticide enter the human body, health suffers directly. The use of DDT powder, for example, brings on diseases of breathing. Coming into contact with a chemical insecticide also affects the nervous system and the glandular system.

• Chemical insecticides pollute the air, the water and the land.
• Their use upsets the balance of the ecosystem.
• Not only the harmful insects but the useful insects are killed too.
• Where DDT powder mixes in, the air and water are poisoned. Aquatic organisms cannot survive in the polluted water, and the ones that do survive slowly lose their power to reproduce.
• The growth and breeding capacity of birds and fish decline.

Accidents happen the moment someone forgets that this is poison. So anyone who handles an insecticide must follow the precautions below.

• Before using an insecticide, study its method of use properly.
• The person spraying must wear suitable protective clothing.
• Above all, never let the insecticide touch the eyes or the mouth.
• While spraying a crop, spray in the direction the wind is blowing, never against it.
• Whatever is left over after spraying must be stored or disposed of safely.
• Never wash the spraying equipment near a source of water.

To keep getting a harvest from farming, the quality of the soil must be maintained continuously. The very chemicals used in excess to raise the harvest can end up spoiling that quality.

The following measures conserve the quality of soil:

• Test the soil: testing the soil from time to time tells which nutrient it needs, and also which kind of crop suits its structure.
• Use suitable farming techniques: rotate the crops, mix the crops, apply agricultural lime, use plenty of organic manure, use less chemical fertiliser and irrigate by a suitable method.
• Use the land properly: a field left fallow slowly loses its fertility, so the land should not be left uncultivated.

Burning leaf litter on the field kills the useful microorganisms living in the soil. On sloping land farmed without terraces, water washes the manure out of the soil and carries it away. So to keep the soil good, never leave the field fallow, never burn leaf litter on it, and cut terraces into a slope before farming it.

A soil test is not the only way of knowing. The plant itself signals which nutrient its soil is short of. In nitrogen poor soil the leaves of the plant turn yellow, and its flowers, fruits and seeds stay small.

A potassium shortage shows first at the edge of the leaf. A leaf whose centre stays green while only the rim turns yellow is signalling that the soil lacks potassium. As the shortage deepens, the rim browns and dries. But when the yellow is not confined to the rim and has spread over most of the blade, the signal points to nitrogen instead.

The effect of soil quality can also be seen by sowing the same kind of seed in two different soils. In fertile soil the plants grow tall and thick, while in nutrient poor soil the same seed gives short, thin plants.