The Role of Fungicides in Integrated Disease Management (IDM)

Every year, fungal diseases such as blast in rice, rust in wheat, early blight in tomatoes, and anthracnose in mangoes kill millions of tonnes of crops, creating enormous losses for Indian farmers. The good news is that we can now defend our harvests before it's too late with safer and more intelligent methods. 

To address this, we can utilize several disease management remedies, and one of the most effective tools is the application of fungicides. 

However, the key is not to overuse fungicides, but to incorporate them strategically into a comprehensive plant protection strategy. 

This is where Integrated Disease Management (IDM) comes in, a combination of various practices that ensures the sustainable and effective management of crop health.

Understanding Plant Diseases and Their Impact on Crops

Indian farmers lose crores of rupees worth of crops every year to harmful plant diseases. These diseases are insidious and undermine plants, lowering yields and in some cases destroying whole crops. The key to saving crops and money is to understand how these diseases work.

Paddy (Rice)

1. Bacterial Leaf Blight (BLB)

Symptoms: Yellowing of the leaf tips that moves down the leaves; the leaves appear dry and scorched.

Favorable Conditions: High humidity, heavy rain, and infected seeds are used.

Effect: Grain filling is poor, and there is a severe reduction in yield (as high as 60 percent in severe cases).

2. Blast Disease

Symptoms: Leaves with small, diamond-shaped, brown spots and panicle neck rot.

Good Conditions: Favorable temperatures: warm days, cool nights, and an overabundance of nitrogen.

Effect: Panicle snaps off; fewer grains and weight.

Wheat

1. Rust Diseases (Brown, Yellow, and Black Rust)

Symptoms: Leaves and stems have reddish-brown, yellow, or black powdery pustules.

Favorable Conditions: Cool and moist weather, particularly in North India.

Effect: Inhibits photosynthesis; decreases grain size and general yield.

2. Karnal Bunt

Symptoms: Black powder with an unpleasant odor that is found within the grains.

Good Conditions: Cloudy sky and moderate temperatures when the plants flower.

Effect: Decreases the market value and limits exportation because of quarantine regulations.

Potato

1. Late Blight

Symptoms: Leaves and stems have dark, water-soaked areas, and fungus growth underneath leaves is white. In storage, tubers decay.

Good Climate: Cool (18–22°C), wet weather.

Effect: Able to kill whole fields within a week when not controlled.

2. Early Blight

Symptoms: Brown spots that have concentric rings; leaves yellow and prematurely fall off.

Favorable Conditions: Warm, moist conditions.

Effect: Makes plants weaker and limits tuber growth.

Tomato and Chilli

1. Early Blight

Symptoms: Circular spots with rings on older leaves, causing defoliation.

Good Conditions: Warm and moist conditions.

Effect: Abnormal fruit development and sunburned fruits.

2. Powdery Mildew

Symptoms: Upper leaf surface covered with white powdery coating.

Good Conditions: Warm and dry days with cool nights.

Effect: Decreases fruit production and photosynthesis.

3. Bacterial Wilt (found in chilli)

Symptoms: Plants will wilt instantly without the yellowing.

Favorable Conditions: Soils that are warm and wet.

Effects: Plants die in the middle of the season, resulting in huge losses.

Grapes

1. Downy Mildew

Symptoms: Yellowish oil spots on the upper surface of leaves and white downy growth on the lower.

Favorable Conditions: High humidity, cloudy weather.

Effect: Fruit set is poor; bunches rot prematurely or drop.

2. Anthracnose (Bird's Eye Disease)

Symptoms: Berries and shoots have dark, sunken spots with a gray center.

Favorable Conditions: Warm and wet conditions.

Effect: Reduces vine growth; decreases the quality and quantity of fruits.

Orange, Lemon, Sweet Lime (Citrus Fruits)

1. Citrus Canker

Symptoms: Corky lesions on leaves, stems, and fruits that are raised and have yellow halos.

Favorable Conditions: Rain driven by the wind, warm temperatures.

Effect: Decreases the size, quality, and shelf life of the fruits.

2. Gummosis

Symptoms: Bark splits open and sticky, brownish gum oozes out of the trunk or branches.

Favorable Conditions: Wounding and bad drainage.

Effect: Makes the plant weaker; limits the movement of nutrients.

Fungal infections account for a significant share of the yearly economic loss caused by plant pests and diseases in India, which is expected to exceed ₹290 billion (about $3.5 billion USD).

What are Fungicides? Types and Their Mode of Action

Fungicides are chemicals or biological products that prevent, control, or kill diseases caused by fungi in plants. They act by preventing the development of fungal spores or killing the fungi that are already on or in the plant. Fungicides can be used to prevent the occurrence of common fungal diseases in crops, such as powdery mildew, rust, and blight, which can otherwise reduce crop yield and quality. 

Here, fungicides may be preventative (applied prior to infection), curative (applied after the appearance of disease), or both, depending on their action. They play a significant role in plant protection and are frequently applied in conjunction with other techniques in Integrated Disease Management (IDM) practices.

Types and Their Mode of Action

Contact Fungicides

Contact fungicides stay on the plant surface and do not enter the plant tissues. They are also referred to as protectant fungicides, and they act by forming a chemical barrier to prevent the germination of fungal spores or invasion of the plant. These fungicides should be applied before the disease and can be easily removed by rain or irrigation. They need to be reapplied regularly to be effective.

Systemic Fungicides

Systemic fungicides are absorbed by the plant and distributed throughout the plant. They are suitable for curative treatments since they can destroy fungi that have already infected the plant. Systemic fungicides are rainfast, which means that the chemical or active component will continue to protect crops even after heavy rain and will not wash away quickly. Nevertheless, systemic fungicides are selective in their action and can only attack specific types of fungi, and hence, accurate diagnosis is critical.

Protectant and Curative Fungicides

Protectant fungicides are primarily applied to prevent infection before it happens, whereas curative fungicides are applied after the first symptoms of disease can be seen. More advanced formulations have combined the two actions, giving a wider window of effective treatment. It is important to use the correct type at the appropriate time to control disease outbreaks without excessive use of chemicals.

Role of Fungicides in Plant Disease Control under IDM

Preventive Use of Fungicides in IDM

The application of fungicides is frequently applied before the occurrence of any disease, particularly when weather conditions or crop development heighten the threat of infection. 

For example, during rainy or humid seasons, crops are more susceptible to fungal diseases. When this happens, you can spray contact fungicides to safeguard the crop before any disease occurs. This proactive measure prevents larger issues in the future and minimizes curative measures.

• Applied before the disease appears to protect crops during high-risk periods.
• Uses contact fungicides to block fungal spores on plant surfaces.
• Helps avoid sudden disease outbreaks and crop losses.
• Reduces the need for emergency (curative) treatments later.
• Based on weather forecasts, crop stage, and past disease history.

Curative Use of Fungicides in IDM

When a disease is observed, systemic fungicides are applied to prevent its propagation. Plants absorb these fungicides and combat the fungus internally. However, these treatments are not blindly performed in IDM. 

Here, you should inspect the field, diagnose the disease, and use fungicides only when needed. This precautionary treatment prevents the wastage of chemicals and prevents the fungus from developing resistance to the treatment.

• Applied after observing early signs of disease.
• Uses systemic fungicides that move inside the plant to stop the infection.
• Requires proper field inspection and disease identification.
• Prevents unnecessary chemical use and wastage.
• Slows down the development of fungicide-resistant fungal strains.

Integrated Approach with Other Disease Management Practices

Fungicides are most effective when used along with other good farming practices. This involves planting disease-resistant seeds, practicing crop rotation, ensuring good drainage, planting at the correct time, and employing natural methods to control pests. When all these factors are combined, the risk of disease can be significantly reduced. Fungicides are then only a fraction of the whole and a long-term solution.

• Combines fungicides with crop rotation, resistant seeds, and biological control.
• Enhances overall disease resistance and crop health.
• Reduces chemical usage and environmental harm.
• Promotes sustainable, long-term farm productivity.
• Ensures better results than using fungicides alone.

Benefits of Using Fungicides within IDM Practices

Disease Control:

When utilized as part of an Integrated Disease Management (IDM) system, fungicides are crucial to crop protection. They are also effective in combating severe fungal diseases such as blights, rusts and mildews when used early or as a precautionary measure. 

As an example, tricyclazole is used to manage blast in paddy, propiconazole to manage rusts on wheat, and metalaxyl + mancozeb to manage late blight on potato. Azoxystrobin or hexaconazole is used to control early blight and powdery mildew in tomatoes and chillies and dimethomorph and copper oxychloride are used to control downy mildew in grapes. 

When such fungicides are used at the right time, this prevents heavy losses and ensures the crops are healthy at the most crucial stages of their growth.

Decreased Chemical Dependency:

Fungicides are applied in IDM only when necessary and in combination with other approaches. This implies fewer spray rounds and reduced chemical consumption. It makes input cost-effective and minimizes negative effects on the soil, water, and the environment.Fungicides can be highly effective when combined with compatible adjuvants such as non-ionic surfactants, spreaders, or stickers, which enhance leaf coverage, penetration, and rainfastness. As an example, applying a silicone-based spreader containing propiconazole provides an even coverage on waxy-leaved plants such as wheat or onions. These mixtures enhance the efficiency of treatments, and farmers can use less product and get better disease control.

Fungicide Resistance Prevention:

Overuse or misuse of fungicides may result in resistance, whereby the fungal diseases will no longer respond to the chemical. IDM encourages fungicide rotation based on a different mode of action and timing, which helps to delay the development of resistance and keeps fungicides effective longer. As an example, in grape growing, downy mildew control has relied on metalaxyl, and this has become ineffective in some areas, but an alternative metalaxyl, dimethomorph, or cymoxanil can be used to regain effectiveness. 

Improved Crop Health and Yield:

Through the planned and limited application of fungicides and adherence to good field practices (such as proper spacing, irrigation, and the use of resistant varieties), the crop remains healthier throughout the season. Good crops lead to improved growth, productivity, and quality of grain or fruits.

Environment-Friendly and Sustainable Farming

IDM is concerned with the joint protection of the crop and the environment. Under the responsible use of fungicides in IDM, there is a reduced risk to non-target organisms, such as bees, earthworms, and beneficial fungi. This enhances soil fertility and promotes the long-term sustainability of the farm.

Precautions and Responsible Use of Fungicides in Farming

Use the Right Fungicide for the Right Disease

Before using any fungicide, it is essential to identify the targeted disease. Fungicides do not act against all fungal diseases. Apply the prescribed product according to the crop and type of infection. This will prevent wastage, save costs, and provide adequate control of the diseases.

Follow the Recommended Dosage and Timing

Avoid overdose and underdose. Excessive use of chemicals can damage the plant, the soil, and beneficial organisms, while inadequate use may fail to effectively manage the disease. Always read the label directions for the proper quantity, mixing proportion, and frequency of application.

Use Protective Equipment While Spraying

Fungicides are chemicals and can pose harmful effects on human health when inhaled or when they come into contact with skin or eyes. Always wear protective clothing, such as gloves, a face mask, goggles, and full-sleeved clothing, when mixing and spraying.

Avoid Spraying During Windy or Rainy Conditions

There is a risk of poor coverage, waste, and drift to non-target sites, such as water bodies or adjacent crops, when spraying in high winds or during rainfall. Spraying should be done during calm, dry weather to guarantee high efficacy and safety.

Rotate Fungicides with Different Modes of Action

Repeated application of the same fungicide may result in resistance, where the fungus becomes unaffected by the treatment. To avoid this, consider alternating fungicides with different modes of action or active ingredients as part of your Integrated Disease Management (IDM) strategy.

Conclusion

Fungicides are very important in the control of fungal diseases, particularly when combined with other disease management strategies. IDM encourages a moderate program, where preventative and curative fungicide applications are combined with cultural, biological, and mechanical controls. 

This not only enhances crop protection but also contributes to environmental sustainability and the long-term profitability of farms. With the responsible and intelligent application of fungicides, you can protect your crops, your health, and the future of agriculture.