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Improvements in Food Resources

Tutormate > CBSE Syllabus-Class 9th Biology > Improvements in Food Resources

08 Weed Control


Narrow leaf weeds and broad leaf weeds are the two types of weeds.


  • Mechanical Methods: These methods include: uprooting, weeding with trowel or ‘khurpi’
  • Cultural Methods: These include the following methods: proper bed preparation, timely sowing of crops, intercropping and crop rotation.
  • Chemical Method: Chemical weed killers called herbicides or weedicides, are sprayed on weeds in order to destroy (kill) them. This is called chemical control of weeds.
  • Biological Control: Biological control of weeds involves the deliberate use of insects or some other organisms which consumes and specifically destroy the weed plants. The best Indian example of biological control is destroying prickly-pear cactus (opuntia) by using the cochineal insects in Maharashtra and Tamil Nadu.


  • Weeds compete with the crops for nutrients, water, space and light. They grow quickly; absorb more nutrients and water thus depriving the crop plants of essential inputs. As a result the growth of the crop is reduced.
  • The weeds act as an alternate host to insects and microorganisms and spreads crop pests.
  • Some weeds may produce toxic substance which may interfere with growth of crop plants.
  • During harvesting, weeds get mixed with crop’s produce to downgrade its quality.


  • Chewing insects: These insects destroy all sort of crop plants.
  • Sucking insects: These insects suck the cell sap from various parts of the plant. Aphids (e.g., Aphis), leaf hoppers (pyrilla), plant bugs.
  • Internal feeders: The internal feeders live inside the plant parts. They are called borers when they live in twigs or roots as sugarcane borers. Pod borer make holes in pods of chick pea and feed on developing grain. They are called weevils when they attack the fruits and seeds such as guava, ber, karela, ghia tori, etc.
  • Grubs (larvae of beetle) and termites:
    • Root cutting types of insects are controlled by mixing insecticide in soil, e.g., chloropyriphos.
    • Stem and leaf cutting and boring type of insects are controlled by dusting or spraying the contact insecticides e.g., malathion, lindane and thiodan.
  • All sap sucking insects can be controlled by spraying systemic insecticides e.g., dimethoate and metasystox. An insecticide entering the plant via the roots or shoots and passing through the tissues is called systemic.


Crop diseases are of following four main types:

  • Seed-borne diseases: These diseases spread through seeds, e.g., “ergot of bajra” or of pearl millet; “leaf spot of rice”; “loose smut of wheat”; red rot of sugarcane; -. They all are cause by fungi.
  • Soil- borne diseases: These diseases spread through the soil and mostly affect roots and stems of crop plants, e.g. “smut of bajra”, “tikka disease of groundnut”.
  • Air-borne disease: These crop diseases are transmitted by the air, e.g., “rust of wheat”, “blast of rice”.
  • Water-borne disease: Pathogens of these crop diseases are transmitted by the water, e.g., “bacterial blight of rice”.
  • Control of crop diseases: All the seed-borne and soil-borne diseases can be controlled by treating the seed or soil. Air-borne diseases are controlled by spraying fungicide solution on infested parts.



Cereals or food grains are stored at three levels. They are:

  • At producer (farmer) level (called rural storage)
  • At trader’s level (this is done by keeping food grains in gunny bags)
  • At FCI (Food Corporation of India) level

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