Types of Chemicals Used in Plant Disease Control and Their Modes of Action
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 in Plant Pathology
1. What is chemical control of plant diseases?
Chemical control of plant diseases is the use of chemical agents such as fungicides, bactericides, and nematicides to prevent or reduce infection in crops. It aims to protect plants from pathogens and minimize yield loss.
- Uses fungicides against fungal pathogens.
- Uses bactericides for bacterial diseases.
- Uses nematicides to control parasitic nematodes.
- Applied as sprays, seed treatments, or soil treatments.
2. How do fungicides control plant diseases?
Fungicides control plant diseases by inhibiting the growth, reproduction, or survival of fungal pathogens. They act either before infection (protective) or after infection (curative).
- Protectant fungicides form a barrier on plant surfaces.
- Systemic fungicides are absorbed and move within plant tissues.
- They may disrupt cell membrane synthesis, respiration, or enzyme activity.
3. What are the types of chemicals used in plant disease control?
The main types of chemicals used in plant disease control include fungicides, bactericides, nematicides, and antibiotics. Each targets a specific group of pathogens.
- Fungicides – control fungal diseases like blight and rust.
- Bactericides – manage bacterial leaf spots and wilts.
- Nematicides – kill or suppress plant-parasitic nematodes.
- Antibiotics – used in limited cases for bacterial infections.
4. What is the difference between protective and systemic fungicides?
The main difference is that protective fungicides act on the plant surface, while systemic fungicides are absorbed and move inside the plant. Their mode of action differs significantly.
- Protective (contact) fungicides: Prevent infection; must be applied before pathogen entry.
- Systemic fungicides: Absorbed into tissues; can stop early infections.
- Systemic types often have specific biochemical targets.
5. Why is chemical control important in agriculture?
Chemical control is important because it provides rapid and reliable protection against severe plant diseases that can cause major yield losses. It supports large-scale food production.
- Prevents epidemics in high-value crops.
- Improves crop quality and market value.
- Reduces economic losses for farmers.
- Acts as part of integrated disease management (IDM).
6. What are the disadvantages of chemical control of plant diseases?
The disadvantages of chemical control include environmental pollution, pathogen resistance, and potential health risks. Overuse can create long-term problems.
- Development of fungicide resistance in pathogens.
- Residue accumulation in soil and water.
- Harm to non-target organisms.
- Increased production costs.
7. What is fungicide resistance and how does it develop?
Fungicide resistance is the ability of a fungal pathogen to survive doses of a fungicide that previously controlled it effectively. It develops through genetic variation and selection pressure.
- Random mutations occur in fungal populations.
- Repeated use of the same fungicide selects resistant strains.
- Resistant fungi multiply and dominate the population.
8. How are chemicals applied for plant disease control?
Chemicals for plant disease control are applied through spraying, seed treatment, soil application, or trunk injection depending on the crop and pathogen. Proper application ensures effectiveness.
- Foliar sprays for leaf and stem diseases.
- Seed treatment to prevent seed-borne infections.
- Soil drenching for root pathogens.
- Trunk injection in perennial trees.
9. Can chemical control be combined with other disease management methods?
Yes, chemical control is often combined with cultural and biological methods in Integrated Disease Management (IDM). This approach improves efficiency and sustainability.
- Use of resistant crop varieties.
- Crop rotation and sanitation practices.
- Application of biological control agents.
- Judicious use of fungicides.
10. What are some examples of chemicals used to control plant diseases?
Common examples of chemicals used in plant disease control include Bordeaux mixture, copper oxychloride, carbendazim, and mancozeb. These are widely used fungicides.
- Bordeaux mixture – a copper-based fungicide for downy mildew.
- Copper oxychloride – controls bacterial and fungal diseases.
- Carbendazim – a systemic fungicide for leaf spots and blights.
- Mancozeb – a broad-spectrum protective fungicide.
