How Do Chemicals Prevent and Manage Plant Diseases?
Plant diseases are something that stops or prevents plants from growing naturally or achieving their maximum growth potential. It is a type of impairment of the normal state of the plant which modifies its vital functions or interrupts it. All of the plants, irrespective of their species, habitat, etc can be affected by various plant diseases. These diseases vary from season to season and depend on the presence of the type of pathogen, the variety of plants, and the environmental conditions. Plant diseases can be biotic or abiotic. Biotic diseases are caused by living organisms known as pathogens whereas Abiotic diseases are caused by external factors and not living organisms.
Control of Plant Diseases
For the prevention of plant diseases, the use of chemical control plays a critical role. There are numerous specific action fungicides that have been developed since the 1960s and a variety of chemicals are available nowadays which are developed and designed to control plant diseases by inhibiting the increment of or by killing the disease-causing pathogens. There are various types of chemicals used for this purpose such as chemicals that control bacteria (bactericides), that control fungi (fungicides), and chemicals that control nematodes (nematicides). These chemicals should be used in a proper and judicious manner for plant disease control.
How to Control Plant Diseases?
To control plant diseases, we should have a thorough knowledge of the disease cycle and the causal agent, host-pathogen interactions in relation to the environmental factors and the cost. We can control plant diseases by choosing the best variety and seeds. For the harvested crops, disease control can be extended through transport, storage, and marketing. The other approaches for controlling plant diseases are biological, cultural, and chemical methods. Of all plant disease control methods, we will learn about the chemical control of plant diseases in this article.
Chemical Control of Plant Diseases
In the prevention of plant diseases, chemical control plays a critical role. Numerous specific action fungicides have been developed since the 1960s. A variety of chemicals are available nowadays that are developed and designed to control plant diseases by inhibiting the growth of or by killing the disease-causing pathogens. There are various types of chemicals - chemicals that control bacteria (bactericides), that control fungi (fungicides), and chemicals that control nematodes (nematicides). These chemicals should be used properly for plant disease control.
Control of Crop and Forest Disease
The chemicals used for plant disease control are applied to seeds, flowers, fruits, foliage, and soil to reduce or prevent infections. The protectants act as a chemical barrier between the plants and the pathogens. The eradicants are designed to kill the pathogens present in the seeds or vegetative propagative organs such as tubers, bulbs, or corms and in the soil. The therapeutic chemicals are used to combat in-progress infection.
Chemical Control Methods
The soil treatments kill the nematodes, bacteria, and fungi inhabiting the soil. The eradication of these biotic pathogens can be done using steam and chemical fumigants. The nematodes that are born in the soil can be killed by liquid nematicides or granular nematicides. Generally, the soil is treated before plantation, but a few fungicides are mixed with the soil at the time of plantation or after it.
The seeds, bulbs, tubers, and corms are frequently treated with chemicals to get rid of pathogens - fungi, bacteria, and nematodes. This helps in protecting the seeds, bulbs, corms, and tubers from the pathogen present in the soil - mainly the fungi, which is the cause of the decay and the damping off. The seeds are also treated with fungicides which they absorb and get protection for the growing seedling.
The protective dust and sprays are used to prevent infection in foliage and the fruit of crops. There is a wide range of chemical dust and sprays. They are not absorbed by the plant or translocated through the plant, and hence they protect only those parts of the plant treated before invasion by the pathogen. A second spray is always recommended and required as the first layer may be washed away by the wind, rain, or irrigation. There is a possibility of breaking down by the sunlight also.
FAQs on Chemical Control of Plant Diseases: Complete Guide
1. What is meant by the chemical control of plant diseases?
The chemical control of plant diseases is a method of plant protection that involves the application of specialised chemicals, such as pesticides, to prevent, manage, or eradicate diseases caused by pathogens like fungi, bacteria, and nematodes. These chemicals act as a protective barrier, inhibit pathogen growth, or kill the harmful organisms, thereby safeguarding crop health and yield.
2. What are the main types of chemicals used to control plant diseases?
The chemicals used for managing plant diseases are broadly categorised based on the target pathogen. The primary types include:
Fungicides: Chemicals specifically designed to control fungal diseases like rusts, mildews, and blights.
Bactericides: Used to manage diseases caused by bacteria, such as bacterial spots and wilts. Copper-based compounds are common examples.
Nematicides: Target plant-parasitic nematodes, which are microscopic roundworms that damage plant roots.
Herbicides: Although used for weed control, they can indirectly manage disease by eliminating host plants for certain pathogens.
Insecticides: Control insect pests that can act as vectors, transmitting viral or bacterial diseases from one plant to another.
3. What are the primary advantages of using chemical methods for plant disease control?
The main advantages of chemical control in agriculture include its effectiveness and speed. Chemicals can act quickly to stop a widespread infection, preventing significant crop loss. They are often highly effective, reliable, and readily available for various types of diseases. Furthermore, their application can be relatively easy and cost-effective, especially for large-scale farming operations, leading to predictable results in crop protection.
4. What are the major disadvantages or risks associated with the chemical control of plant diseases?
Despite their benefits, chemical controls have significant disadvantages. A major risk is their potential harm to non-target organisms, including beneficial insects, soil microbes, and even humans. Overuse can lead to the development of pesticide-resistant pathogens, making the chemicals ineffective over time. Another concern is biomagnification, where chemical residues accumulate in the food chain, posing a threat to the entire ecosystem.
5. How do systemic and non-systemic (contact) fungicides differ in their mode of action?
Systemic and non-systemic fungicides differ in how they protect the plant. Non-systemic (contact) fungicides remain on the plant's surface where they are applied and act as a protective barrier, killing pathogens upon contact before they can infect the plant tissue. In contrast, systemic fungicides are absorbed by the plant and translocated through its vascular tissues (xylem or phloem). This allows them to protect new growth and control pathogens that have already entered the plant.
6. Why can't the same chemical be used to control all types of plant diseases?
The same chemical cannot control all plant diseases due to the principle of selective toxicity. Different pathogens, like fungi, bacteria, and nematodes, have unique biological and cellular structures. A fungicide is designed to disrupt specific metabolic pathways found in fungi, which are absent in bacteria. Similarly, a nematicide targets the nervous system of nematodes, which is ineffective against fungi or bacteria. Therefore, a specific chemical is formulated to target the unique biology of a particular type of pathogen for effective control.
7. How does soil fumigation work as a method of chemical disease control before planting?
Soil fumigation is a preemptive chemical control method where a volatile chemical (a fumigant) is injected into the soil before planting. The chemical turns into a gas and spreads through the air spaces in the soil. This gas is toxic to a broad spectrum of soil-borne pathogens, including harmful fungi, nematodes, bacteria, and weed seeds. By sterilising the soil, fumigation eliminates the disease-causing organisms, creating a healthier environment for the new crop to grow without early-stage infections from the soil.
8. Why is developing resistance to chemicals a major concern in plant disease management?
The development of resistance is a critical concern because it renders previously effective chemicals useless. When a chemical is used repeatedly, it creates a strong selective pressure. Pathogens that happen to have a natural genetic mutation allowing them to survive the chemical will reproduce, passing this resistance trait to their offspring. Over time, the entire pathogen population can become resistant. This forces farmers to use higher doses or switch to newer, often more expensive chemicals, escalating costs and environmental risks in a continuous cycle.
