Protecting and storing the crop

Weeds, pests and diseases

A crop can be lost even when the seed, the soil and the water are good.

• Weeds are unwanted plants in a crop field. They compete with the crop for nutrients, water, light and space, and the yield falls. Xanthium (gokhroo), Parthenium (gajar ghas) and Cyperus rotundus (motha) are weeds.
• Insect pests attack a plant in three ways. They cut the root, the stem and the leaves. They suck cell sap from different parts. They bore into stems and fruits.
• Diseases are caused by pathogens: bacteria, fungi and viruses. They spread through soil, water and air.

Protecting the crop

Farmers use pesticides to fight these enemies. Herbicides kill weeds, insecticides kill insects and fungicides kill fungi. They work, but they are poisonous. If they are used too much, they harm the soil, the water and animals. In the chapter Our Environment, you saw that a chemical that is not broken down builds up along a food chain and reaches human beings.

So farmers prefer methods that need little or no chemical.

• Prepare the field well. Ploughing and levelling destroy many weeds and pests.
• Sow in time. A crop sown at the right time grows strong before the pests arrive.
• Use inter-cropping and crop rotation. The pests and diseases of one crop do not build up in the field.
• Grow resistant varieties.
• Plough deeply in summer. The summer sun and the turned soil kill weeds and pests.
• Use natural helpers. Neem leaves kept among the stored grain keep pests away.

Storing the grain

Grain is stored for months after the harvest. Stored grain is lost to two kinds of cause.

• Biotic causes come from living things: insects, rodents, fungi, mites and bacteria.
• Abiotic causes come from the surroundings: too much moisture and the wrong temperature.

These cause a loss in weight, poor germination, discolouration and a poor price at the market.

There are three steps to prevent the loss.

1. Clean the grain strictly before it is stored.
2. Dry it well, first in the sun and then in the shade.
3. Fumigate the store with chemicals that kill pests.

How much does treatment save?

Set the grain, the share lost each month and the time. See how much grain the treatment saves.

Try it in Python

The program follows two stores for a year, one untreated and one cleaned, dried and fumigated.

Practise with new numbers

Common mistakes

• "Herbicides kill insects." Herbicides kill weeds, insecticides kill insects and fungicides kill fungi.
• "More pesticide is always better." Too much poisons the soil, the water and animals, and it builds up along food chains.
• "Weeds only take up space." Weeds also take nutrients, water and light.
• "Dry grain is safe for ever." Rats, insects and fungi still attack grain unless the store is clean and treated.

Remember these

• Weeds, insect pests and diseases lower the yield. Pathogens are bacteria, fungi and viruses.
• Herbicides, insecticides and fungicides are pesticides. They are poisonous, so they must be used with care.
• A good field, sowing in time, inter-cropping, crop rotation, resistant varieties and summer ploughing cut the need for pesticides.
• Stored grain is lost to biotic causes, such as insects and rodents, and abiotic causes, such as moisture.
• Prevent the loss by cleaning, drying and fumigating.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Why are weeds harmful to a crop?

2. Name the three kinds of pathogens that cause crop diseases.

3. Give two ways to protect a crop without spraying a chemical.

4. Give one biotic cause and one abiotic cause of loss in a grain store.

5. List the three steps to prepare grain for storage.