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Crop Production and Management - Protection from Weeds and Pests

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Weeds are undesirable plants that grow naturally along with crops and compete for nutrients (N,P,KN, P, K), water, space, and light.

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The removal of weeds is called weeding. It is necessary because weeds interfere with harvesting and may be poisonous for animals and human beings.

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Tilling before sowing of crops helps in uprooting and killing of weeds, which may then dry up and get mixed with the soil.

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Manual removal includes physical removal of weeds by uprooting or cutting them close to the ground from time to time, often using a 'khurpi' or a 'seed drill'.

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Weedicides are certain chemicals used to control weeds, such as 2,4−D2,4-D (2,4-Dichlorophenoxyacetic acid). They are diluted with water and sprayed in the fields.

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Pests are organisms like insects, rodents, and fungi that damage crops. Pesticides (including insecticides and rodenticides) are used to eliminate them.

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Biological control involves using natural enemies of pests to keep their population in check, reducing the reliance on harmful chemicals.

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Safety precautions are vital while spraying weedicides or pesticides; farmers should cover their nose and mouth with a piece of cloth to avoid inhaling these chemicals.

📐Formulae

Concentration of Weedicide=Volume of WeedicideVolume of Water (Solvent)\text{Concentration of Weedicide} = \frac{\text{Volume of Weedicide}}{\text{Volume of Water (Solvent)}}

Crop Yield∝1Weed Density\text{Crop Yield} \propto \frac{1}{\text{Weed Density}}

Chemical Notation: 2,4−D (2,4-Dichlorophenoxyacetic acid)\text{Chemical Notation: } 2,4-D \text{ (2,4-Dichlorophenoxyacetic acid)}

💡Examples

Problem 1:

Why is it recommended to spray weedicides during the vegetative growth of weeds before flowering and seed formation?

Solution:

Weedicides should be sprayed before weeds produce flowers and seeds to prevent the dispersal of new seeds into the soil.

Explanation:

If weeds are allowed to flower and set seeds, the seed bankseed \ bank in the soil increases, leading to a much higher infestation in the next cropping season. Killing them early ensures they do not reproduce.

Problem 2:

A farmer finds that his wheat crop is infested with 'Chenopodium' (Bathua). What chemical might he use, and why does it not harm the wheat plant?

Solution:

The farmer can use a selective weedicide like 2,4−D2,4-D.

Explanation:

Many weedicides like 2,4−D2,4-D are selective herbicides. They are designed to kill broad-leaved plants (dicots) like 'Bathua' while leaving narrow-leaved cereal crops (monocots) like wheat (Triticum aestivumTriticum \ aestivum) unharmed.