Biology Topics related to disease and health provide critical insights into human physiology and medicine.
Crop Protection Management & Methods in Agriculture
Field crops are infested with a variety of pests. A pest is any destructive organism that 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. Field crops are infested by a large number of insect pests and diseases. If these pests are not controlled at the appropriate time they can damage the crops to the extent of 50 to 70 percent.
There are various methods by which insects and diseases can be controlled. One of 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). Thus, 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. However, one should try to avoid the use of these toxic chemicals (pesticides) as they cause environmental pollution. In fact, it would be far better if we adopt preventive measures rather than allowing the crops to be infested by pests and then control them with pesticides.
Some of the preventive measures against pests are the following:
- Use of resistant varieties of crop plants
- Selection of optimum time for sowing the crops
- Crop rotation and multiple cropping
- Clean cultivation
- Summer ploughing
For example, a humid and warm climate is regarded as more favourable for infestation of insect pests and diseases. That is why “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 cultivated fields. In other words, plants other than crops are the weeds. Weeds tend to compete with crops for food (water and nutrients), space, and light. In comparison to cultivated crops, 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 a large number of seeds.
In fact, weeds take up all the nutrients and reduce the growth of crops in various ways. Therefore, the removal of weed plants from cultivated fields in the early stage of the crop is essential to harvest high input returns in terms of high yield. In unirrigated conditions, weeds affect the water availability and in irrigated conditions, there is competition for nutrient uptake between weeds and crop plants.
For example, barley or mustard plants act as weeds in a wheat field and compete with crops for nutrition. Likewise, wild sorghum grown in cultivated crop fields of sorghum (jowar) acts as a weed plant and competes with the crop for water and nutrients.
Types of Weeds
Infestation of weeds is more during the ‘kharif’ season than in the ‘rabi’ season. Based on the morphology of plants, weeds can be classified into narrow-leaf weeds and broad-leaf weeds.
Further, during the ‘kharif’ season, short duration (e.g., maize and millet), short saturated (e.g., groundnut), and slow growing (e.g., pigeon pea) crops are more susceptible to weeds. The critical period for controlling weeds in these crops is 35 to 45 days.
Methods of Weed Control
Weeds can be controlled by the following methods:
1. Mechanical Methods:
These include the following methods: uprooting, weeding with a trowel or ‘khurpi’ or harrow (a comb-like implement), hand hoeing (scraping), interculture, ploughing, burning and flooding.
The process of removing weeds from crop fields is called weeding. Weeding can be done by the following methods:
- Weeds may be pulled out with the hand. Ploughing helps in removing a large number of weeds because it uproots the majority of them.
- Before sowing or transplantation, weeds are removed by using a big comb like a harrow. Harrows cannot be used in standing crops because they will also uproot crop plants.
- The weeds which appear during the growth of crop plants are removed manually by using a trowel (khurpa).
2. 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:
- 2, 4-D (2, 4-Dichlorophenoxy acetic acid)
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 the eradication of prickly-pear cactus (Opuntia) by using the cochineal insects in Maharashtra and Tamil Nadu. Generally, a combination of one or more of these weed control methods is employed to get good results. Aquatic weeds are controlled by the fish grass carp.
Effects of Weeds on Crop Plants
- The growth of weeds in crop fields is harmful because they compete with the crops for nutrients, water, space, and light. Weeds are generally more efficient than crop plants.
- They grow quickly, absorb more nutrients and water and deprive the crop plants of essential inputs. As a result, the growth of the crop is reduced.
- The weeds spread crop pests and diseases by acting as alternate hosts to insects and microorganisms.
- Some weeds may produce toxic substances which may interfere with the growth of crop plants.
- During harvesting, weeds get mixed with the crop’s produce to downgrade its quality.
Insect Pest Control
Many insects are serious pests of plants. They attack all stages, parts, and products of plants.
Insects attack the crop plants in the following three ways:
1. Chewing Insects:
The chewing insects destroy all sorts of crop plants. They cut the root, stem, and leaf of crop plants with the help of their chewing mouthparts. Thus, chewing insects tear off bits of leaves, and delicate branches, chew them, and then swallow them, e.g., locusts, grasshoppers (Hieroglyphics), caterpillars, grubs, etc.
2. 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 (e.g., Aphis), leaf hoppers (Pyrilla), plant bugs (Gundhi bug of rice, painted bug or Bagrada of cruciferous plants, and red cotton bug or Dysdercus). They possess piercing-sucking mouthparts. Sucking insects make fine punctures in the skin of the plants with their needle-like, hollow beaks and suck the sap.
3. 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 borers make holes in pods of chickpeas and feed on developing grain. They are called weevils when they attack the fruits and seeds such as cotton-boll weevils and grain weevils. The maggots of fruit flies live inside the fruits such as guava, her, karela, ghia tori, etc., and render them unfit for human consumption. Further, grubs (larvae of beetle) and termites (e.g., Microtomes obese and Odontotermes obesus damage sugarcane) 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:
- Root-cutting types of insects are controlled by mixing insecticide in soil, e.g., chlorpyrifos.
- Stem and leaf cutting and boring types 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.
- A systemic insecticide harmlessly penetrates the tissues of the host plant and poisons insects feeding on it (e.g., Aphids).