Question 1 What is weed? How weeds affects growth of crop plant?
Question 2 What are the features of weeds?
Question 3 How can we control weeds?
Question 4 What is a pest? Enlist various pests of crop plant?
Question 5 How do insect pest attack crop plant?
Question 6 Name few weeds of Kharif and Rabi season?
Question 7 How are diseases transmitted to crop plant?
Question 8 What are the three level of storage of grains?
Question 9 Name the abiotic factors responsible for loss of grain during storage?
Question 10 How grains can be prevented from loss during storage?
Crop Protection Management
A pest is any destructive organism which causes great economic loss by destroying crop plants or products obtained from them. Pests of crop plants include weeds, insects, mites, nematodes, rodents, fungi, bacteria and viruses.
There are various methods by which insects and diseases can be controlled.The most common and effective methods is the use of pesticides or biocides which include insecticides (for killing the insects), weedicides (for killing the weeds) and fungicides (for killing the fungi).
Chemicals (poisons) used to kill pests, e.g. weeds, insects, mites, rodents and fungi are called pesticides. These chemicals (i.e., pesticides) are sprayed on crop plants or used for treating seeds and soil.
Some of the preventive measures of pests are the following:
1) Use of resistant varieties of crop plants;
2) Selection of optimum time of sowing the crops;
3)Crop rotation and multiple cropping
4) Clean cultivation:
5) Summer ploughing.
For example: humid and warm climate is regarded as more favourable for infestation of insect pests and diseases. Kharif crops (e.g.. maize, millet) are more prone to these pests in contrast to “rabi” crops (e.g., wheat, gram, sugarcane, pea, etc.)
Weeds are unwanted plants in the cultivated fields. Weeds tend to compete with the crops for food (water and nutrients), space and light.
The seeds of weeds, germinate easily, their seedlings grow faster, they flower early, their seed production begins after a short growth period and they produce large number of seeds. In fact, weeds take up all the nutrients and reduce the growth of crop in various ways. Therefore, removal of weed plants from cultivated field in early stage of crop is essential to harvest high input returns in terms of high yield.
In unirrigated condition weeds affect the water availability and in irrigated condition there is competition for nutrient uptake between weeds and crop plants.
For example: 1) barley or mustard plants act as weeds in a wheat field and compete with crop for nutrition.
2) Wild sorghum grown in cultivated crop fields of sorghum (jowar) acts as a weed plant and compete with crop for water and nutrients.
Types of weeds
Weeds can be classified into narrow leaf weeds and broad-leaf weeds.
Some of the important weeds of ‘kharif’ season are the following:
1) Nutgrass or Motha
2) Wild sorghum or Jangli jowar
Some of the important weeds of ‘rabi’ season which infest wheat crop are the following :
2) Jangali jaii
Methods of weed control
Weeds can be controlled by following methods:
1) Mechanical methods. These include the following methods: uprooting, weeding with trowel or khurpi or harrow (a comb-like implement), hand hoeing (scraping), interculture, ploughing, burning and flooding.
The process of removing the weeds from crop field is called weeding.It can be done by the following methods:
1) Weeds may be pulled out with hand.
2) Before sowing or transplantation, weeds are removed by using a big comb like harrow.Harrow cannot be used in standing crops because it will also uproot the crop plants. Cultural methods. They include the following methods: proper bed preparation.
timely sowing of crops, intercropping and crop rotation
3)Chemical methods: Chemical weed killers, called herbicides or weedicides, are sprayed on weeds to destroy (kill) them. This is called chemical control of weeds. Some common examples of weedicides are the following: (1) 2,4-D (2,4-Dichlorophenoxy acetic acid); (2)Atrazine (3) Fluchloralin (4) Isoproturon
4) Biological control: Biological control of weeds involves the deliberate use of insects or some other organisms which consume and specifically destroy the weed plants.
The best Indian example of biological control is eradication of prickly-pear cactus (Opuntia) by using the cochineal insects.
Insect Pest Control
Insects attack the crop plants in the following three ways:
Chewing insects: The chewing insects destroy all sort of crop plants. They cut root, stem and leaf of crop plants by the help of their chewing mouth parts.
For eg. locusts, grasshoppers , caterpillars, grubs, etc.
Sucking insects: The sucking insects suck the cell sap from various parts of the plant. They include various common pests of crop plants such as aphids, leaf hoppers, plant bugs.
Sucking insects make fine punctures in the skin of the plants with their needle-like hollow beaks and suck the sap.
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 cotton-boll weevil and grain weevil. The maggots of fruit-flies live inside the fruits.
Grubs (larvae of beetle) and termites attack the root zone of crops and then reach the aerial parts causing great damage.
Infestation of different types of insect pests can be controlled by the following methods:
1) Root cutting types of insects are controlled by mixing insecticide in soil, e.g chloropyriphos.
2) Stem and leaf cutting and boring type of insects are controlled by dusting or spraying the contact insecticides e.g., malathion, lindane and thiodan.
3) All sap sucking insects can be controlled by spraying systemic insecticides.
e.g: dimethoate and metasystox.
Diseases of Crop Plants
When pathogens get favourable conditions for their growth and propagation, they spread and infest the crop plants causing diseases.
Depending upon their mode of occurrence, crop diseases are of following four main types:
1) Seed-borne diseases: These diseases are spread through seeds, e.g: ergot of
bajra or of pearl millet; leaf spot of rice, loose smut of wheat- all are caused by
2) Soil-borne diseases: These diseases are spread through the soil and mostly affect roots and stems of crop plants, e.g., smut of bajra, tikka disease of groundnut.
3) Air-borne diseases: These crop diseases are transmitted by the air, e.g, rust of wheat, blast of rice, etc. Air-borne diseases attack all aerial parts of the plants, e.g.. leaf, flower, and fruits.
4) Water-borne diseases: Pathogens of these crop diseases are transmitted by the water, e.g.. bacterial blight of rice.
Storage of Grains
Cereal or food grains are stored at following three levels.
1) At producer(farmer) level (called rural storage)
2) At trader’s level (this is done by keeping food grains in gunny bags,
3) At FCI (Food Corporation of India) level (This is done by storing grains in silos)
During storage damage of grains can take place by following two main types of factors:
1) Biotic factors such as insects , rodents( house rat, house mouse, lesser bandicoot rat), birds (e.g, parakeet, sparrow, bulbul, blue rock pigeon, crow, etc), mites and bacteria.
2) Abiotic factors such as moisture contents and temperature.
(a) Effect of temperature. The growth of insects and microorganisms in the stored food materials depends upon the fluctuation of temperature. As the maximum growth rate of the insects is at a higher temperature at 30°C to 32°C, the microorganisms and enzymes are most active at 30°C to 40°C.
Therefore, the food-grains / materials should be stored at lower temperature, ie. below 30°C, then the insects and microorganisms and enzymes will become less active and the damage of material is minimised.
(b) Effect of moisture: For safe-storage, the moisture content of the food-grains should be 14 per cent by weight or less. The greater amount of moisture present in food grains increases the rate of decay of food materials caused by microorganisms and enzymes and the population of insects increases rapidly. When these insects respire they release a lot of heat, so the temperature of stored food grain rises. The rise in temperature of stored food-grains due to the heat released by the respiration of a large number of insects microorganisms (fungi such as molds, yeast, etc.) is called dry heating of food grains.
Disadvantage of the presence of greater moisture is that, it increases the size of the food-grains due to which these grains required more space.
(c) Effect of humidity: The moisture contents present in air is known as humidity.
It promotes the growth of moulds (e.g., Mucor, Penicillium) on the stored food materials.High humidity content also initiates the germination process of stored seeds which also releases the heat.
The rise in temperature of stored food grains due to the growth of moulds and fungi and germination of stored food-grains under high humidity conditions of air is called wet heating or damp grain heating.
Combination of biotic and abiotic factors causes infestation of insects, degradation in quality, loss in weight, poor germinability, discolouration of produce, poor marketability and economic loss.
Preventive and control measures
Biotic and abiotic factors which cause destruction of grains during storage can be prevented and controlled by using the following methods.
1) Cleaning of the produce before storage: The grains and other agriculture produce should be properly cleaned and dried in sun before their storage. They should be filled in new gunny bags before keeping in godowns, warehoused or stores.
2) Safe and proper storage. Godown, ware houses and stores should be properly cleaned, dried and repaired. Pathways (alleys) should be provided between the stacks of grain-filled bags, for the periodic inspection, for spraying or for fumigation.
For the large scale storage of grains, the grain silos are used. The silos are big and tall cylindrical structures. They store different stocks of food items at different levels. Silos are provided with outlets at different levels to withdraw the desired stock of grains.
3) Fumigation: Chemical pesticides are used as fumigants, i.e. the solution of pesticide is converted into fumes. These fumes kill the insect pests and other harmful biological agents (pathogens).