Indian agriculture is under a silent threat of fungal diseases. They are usually not detected until they bring about observable harm-yellowing of leaves, rotting of fruits, or low yields. To address this, we use fungicides, which are an essential remedy for crop protection.
This article addresses the different types of fungicides, their classification, mode of action, and their use under Indian farming conditions.
Understanding Fungicides in Crop Protection
Fungicides are chemical or biological agents that control or prevent fungal diseases in crops.
Different parts of plants are infected by fungi like rust, smut, blight, and mildew that weaken the health of the plant, resulting in low production. These fungi kill crops by infecting them, and fungicides eliminate them or stop their proliferation.
They are used in different forms, i.e., sprays, powders, granules, or seed treatments, and on a large variety of crops, i.e., paddy, wheat, vegetables, and fruits. Fungicides may act on the surface of the plant or penetrate the plant system to provide deeper protection.
Why Are Fungicides Necessary in Modern Farming?
Fungicides are an important part of contemporary agriculture since fungal infections often lead to severe losses of crops, decreasing yield, quality, and profits. With more intensive farming and less predictable climatic patterns, there has been an increased risk of fungal outbreaks. Fungicides are commonly used to safeguard crops and provide security to the agricultural, horticultural, and gardening sectors at scale.
These are some of the reasons why fungicides play a significant role in contemporary agriculture:
1. Prevent Crop Losses from Fungal Diseases:
Fungal diseases such as powdery mildew, rust, leaf spot, and blight can spread rapidly and devastate vast fields of crops. These diseases can be prevented with fungicides like Mancozeb (a contact fungicide that disrupts fungal enzyme activity) and Tebuconazole (a systemic fungicide that inhibits ergosterol biosynthesis in fungal cell membranes), allowing crops to be saved before they are severely damaged.
2. Improve Crop Yield and Quality
Healthy plants produce more and better fruits, grains, or vegetables. Fungicides also aid in the prevention of fungal infection in plants, thereby resulting in high productivity and more appealing produce, which is vital in the market and for export.
3. Support High-Value and Commercial Crops
Fungicides are particularly important in high-value crops such as grapes, apples, potatoes and tomatoes. The selling price can be decreased even by a minor fungal infection. Fungicides allow farmers to maintain crop quality and satisfy the market demand, which further helps in gaining better profits through agriculture.
4. Handle Changing Weather Conditions
Due to increasing humidity and unstable rains, fungal diseases are on the increase. Fungicides are a protective measure against these climate-related infections and ensure that farming is more predictable.
Classification of Fungicides by Mode of Action
The mode of action of a fungicide determines its protection or curative effect on the plant. The choice of the right kind of fungicide is influenced by the stage of the disease, crop, and environmental factors.
1. Contact Fungicides
Contact fungicides target the surface of the plant. They form a protective layer that destroys or suppresses fungal spores before they have a chance to enter the plant tissue. These fungicides lack translocation within the plant and need to be applied regularly, particularly following rain or irrigation.
Key Features
- Do not cure fungal infections; only prevent them.
- Persist on the external surface of leaves or stems.
- Easy to wash off in rain; needs to be sprayed more often.
Use Cases
- It is commonly applied to vegetables (tomatoes, chillies, onions) and fruit crops (citrus, guava).
Practical Insight
- Contact fungicides are used in tomato production, applied every week during the monsoon to forestall early blight and leaf spot.
2. Translaminar Fungicides
Translaminar fungicides enter the leaf surface and travel between the top of the leaf and the bottom of the leaf, but they do not travel throughout the entire plant as systemic fungicides do. They provide protection on both sides of the leaf despite being sprayed on one side.
Key Features
- Protect both sides of the leaf.
- Good for spots where complete spray coverage is hard to achieve.
- Do not disseminate to the whole plant system.
Use Cases
- Applicable in leafy crops such as chilies, grapes, and brinjal.
Practical Insight
- A translaminar fungicide is used in chili fields with a bushy growth to cover the undersides of the leaves where the fungal spores tend to settle.
3. Systemic Fungicides
Systemic fungicides are absorbed by the leaves, stems, or roots of the plant and then carried through the vascular system. These fungicides offer internal protection and are mostly used in the prevention and management of fungal diseases that have already invaded the crop.
Key Features
- Translocate within the plant.
- Offer more lasting protection.
- Active even after the symptoms of the disease have been manifested (curative action).
Use Cases
- Commonly applied in field crops such as paddy (sheath blight, blast), wheat (rusts and leaf blotches).
- Useful when the fungal disease has already found its way into the plant and started to propagate.
Practical Insight
- In a wheat crop at flowering, when rust is spotted, an early application of a systemic fungicide may prevent further development and prevent future grain production.
4. Preventive Fungicides & Curative Fungicides
Another classification of fungicides is their application to the development of the disease.
Preventive Fungicides
These fungicides are used prior to the appearance of any disease. They create a barrier to the surface of the plant that prevents the fungal spores from germinating or gaining access into the plant. Their primary aim is to avoid the onset of infection.
- Administered before getting infected.
- Prevent germination of fungal spores or their entry into the plant.
- The majority of the contact fungicides belong to this category.
- Most effective when applied in high-risk times (e.g., pre-monsoon, humid spells).
Curative Fungicides
They are used after the fungal infection has begun. They act by entering into the plant tissue, where they inhibit the growth or movement of the fungus within the plant. Nevertheless, they are most effective when administered at early stages of infection.
- Used once the infection has already begun.
- Prevent the growth and transmission of the current fungal pathogens.
- They are usually systemic.
- Most effective at early stages of infection-less effective when the disease is advanced.
Best Practice
- Apply preventive fungicides as a part of a seasonal spray program and curative fungicides when you first see signs of infection. Rotating both helps manage the disease effectively.
Classification of Fungicides by Chemical Group
Fungicides are also classified according to their chemical structure and mode of biological action. Different groups work against different forms of fungus. Understanding these groupings helps in appropriate selection, rotation, and resistance management.
Biological Fungicides:
These are living organisms (beneficial fungi or bacteria) that naturally compete with disease-causing fungi or produce antifungal chemicals.
- Type: Biological; environmentally friendly.
- Mode of Action: Competition or inhibition of pathogenic fungi in the root zone or leaf surface.
- Applications: Seed treatment, foliar sprays, organic farming.
- Benefits: Non-toxic, environmentally friendly, applicable in sustainable farming.
- Limitation: Lower activity and possibly the need to reapply.
Copper-Based Fungicides
These fungicides include copper ions, which destroy fungi by interrupting their enzyme systems.
- Type: Contact fungicide.
- Mode of Action: Multi-site activity; effective against a broad range of fungi.
- Use Cases: Paddy (brown spot), citrus (leaf spot), and vegetables (early blight in tomato).
- Caution: Excessive use may lead to copper buildup in soil, affecting soil microbes and fertility.
Sulfur-Based Fungicides
Sulfur prevents fungal respiration and is most effective in treating surface-level fungal diseases such as powdery mildew.
- Type: Contact fungicide.
- Mode of Action: Disrupts energy production in fungi.
- Use Cases: Grapes, okra, cucurbits (bottle gourd, ridge gourd).
- Advantages: Economical and low risk of resistance.
Triazoles
Triazoles are systemic fungicides that prevent the production of sterols, which are required for fungal cell membranes.
- Type: Systemic fungicide.
- Mode of Action: Single-site; both preventive and early curative.
- Use Cases: Wheat (rust), groundnut (leaf spot), mustard.
- Caution: Fungi can develop resistance; it should be rotated with other fungicide groups.
Dithiocarbamates
These are older but still commonly used multi-site fungicides that work against a variety of fungal diseases.
- Type: Contact fungicide.
- Mode of Action: Multi-site; interferes with multiple fungal enzymes.
- Use Cases: Paddy, banana, tomato, potato.
- Advantages: Low resistance risk.
- Limitation: Requires regular application due to a lack of systemic action.
Strobilurins
Mitochondrial respiration in fungi is blocked by strobilurins, and the fungus is unable to generate energy.
- Type: Broad-spectrum fungicide.
- Mode of Action: Preventive and limited curative.
- Use Cases: Fruits, vegetables, and pulses.
- Benefits: Guarding against new plant growth and enhancing plant vigor.
- Limitations: There is a risk of high resistance when overused.
Common Crops and Their Associated Fungal Diseases
A large number of crops are susceptible to fungal diseases, which lower the quality and quantity of products unless controlled timely. Farmers can learn more about diseases prevalent in particular crops and use preferable measures to prevent or treat such diseases in advance to save their crops. The following are some of the common crops and fungal diseases to which they are most prone.
Paddy
- Diseases: Blast, Sheath Blight, Brown Spot.
- Management: Use of systemic and preventive fungicides during early growth and flowering stages.
Wheat
- Diseases: Rust, Leaf Blotch, Powdery Mildew.
Strategy: Use a mixture of curative and preventive sprays in heading and grain-filling periods.
Vegetables (Tomato, Onion, Chili)
- Diseases: Early Blight, Downy Mildew, Anthracnose.
- Tip: Rotate fungicide classes frequently to prevent resistance.
Fruits (Banana, Grapes, Citrus)
- Diseases: Sigatoka (Banana), Powdery Mildew (Grapes), Citrus Canker.
- Management: Use of protective and systemic fungicides depending on fruiting stage.
Applications and Best Practices for Fungicide Use
Resistance Management
Repeated use of the same fungicide can cause fungi to become resistant. To avoid this:
- Rotate between different chemical groups.
- Apply a combination of both broad-spectrum and specific fungicides.
- Combine non-chemical practices such as crop rotation and resistant varieties.
Timing and Frequency
- Use preventive fungicides prior to disease symptoms.
- Apply curative fungicides during the early symptoms.
- Use seasonal spray programs suggested by local agricultural authorities.
Application Methods
- Foliar sprays: This is the most common method.
- Seed treatment: Prevents early infections of seedlings.
- Soil drenching: It is applied in root-related fungal issues.
Safety Measures
- Wear gloves, a mask, and protective clothing at all times.
- Never spray in windy times or when bees are present.
- Follow the label instructions carefully.
Conclusion: Choosing the Right Fungicide Strategy
When it comes to fungicides, there is no universal prescription. There are different challenges in every crop, region, and season. An effective fungicide management plan incorporates preventive and curative modes of action rotation, and safe and responsible practices. Farmers can understand the nature of fungicides and their usage to ensure that their crops are better safeguarded, productivity is improved, and long-term soil and environmental well-being are guaranteed.
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