Unit 3 - EIL and ETL | Principles of Integrated Disease Management

Syllabus: Calculation and dynamics of economic injury level and importance of Economic threshold level. Methods of disease control: Host plant resistance, cultural, mechanical, physical, legislative, biological and chemical control.

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Economic Injury Level

The Economic Injury Level (EIL) is a critical concept in Integrated Pest Management (IPM) and Integrated Disease Management (IDM) that helps farmers make informed decisions regarding the need for pest or disease control. EIL is the pest population level at which the expected crop damage exceeds the cost of implementing control measures. Similarly, the Economic Threshold (ET) is the pest population level at which control measures should be initiated to prevent the pest population from reaching the EIL.

Calculation of Economic Injury Level (EIL):

The EIL can be calculated using the following formula:

EIL = C / V × DI × K


  • C = the cost of pest control per unit area (e.g., per acre)
  • V = the market value of the crop per unit yield (e.g., per bushel)
  • DI = the yield loss per pest per unit area (e.g., per insect per acre)
  • K = the proportion of the pest population that is killed by the control measure (e.g., 0.8 for 80% mortality)

Dynamics of Economic Injury Level (EIL):

The EIL is not a fixed value and can vary based on several factors:

1. Crop Value and Market Prices: Changes in the market prices of crops can influence EIL. When crop prices are higher, the EIL may be lower because the economic threshold for control is lower.

2. Pest or Disease Population Dynamics: As the pest or disease population changes over time, the EIL may fluctuate. A higher pest population may lead to a lower EIL, indicating that control measures should be implemented at lower pest densities.

3. Pest Resistance and Control Effectiveness: The development of pest resistance or changes in the effectiveness of control measures can impact the EIL. Increased resistance may require higher control efforts and affect the EIL.

4. Environmental Factors: Environmental conditions can influence pest or disease populations. Factors like weather, climate, and habitat may affect the EIL by altering pest growth and survival rates.

5. Crop Growth Stage: The stage of crop growth can also influence EIL. Some crops may tolerate pests or diseases better at certain growth stages, leading to adjustments in the EIL.

The Economic Injury Level (EIL) is a dynamic and important concept in Integrated Disease Management (IDM) and Integrated Pest Management (IPM). By calculating the EIL, farmers can determine the economic threshold for initiating control measures and make informed decisions about when and how to manage pests or diseases effectively and economically. Continuous monitoring and consideration of various factors that influence the EIL are essential for the successful implementation of IDM and IPM strategies in sustainable agricultural practices.

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Economic Threshold Level (ETL)

The term "ETL" stands for "Economic Threshold Level," and it is a concept used in integrated pest management (IPM) and integrated disease management (IDM). The economic threshold level is a point at which the population of a pest or disease reaches a certain level where control measures should be initiated to prevent economic losses.

In other words, the economic threshold level represents the point at which the cost of implementing control measures, such as pesticide applications, is justified by the potential economic damage caused by the pest or disease. Below this threshold level, the economic benefits of control measures might not outweigh the costs. Understanding the importance of ETL is vital for effective and sustainable agricultural practices. 

Importance of Economic Threshold Level (ETL):

Here are the key reasons why ETL is essential:

1. Cost-Effective Management: The ETL helps farmers optimise the use of control measures. By initiating control when pest or disease populations reach the ETL, farmers can avoid unnecessary applications of pesticides or other control tactics when they are not economically justified. This approach minimises production costs while effectively managing pest or disease populations.

2. Preventing Economic Losses: Implementing control measures at the ETL prevents pest or disease populations from reaching damaging levels that can cause economic losses. Early detection and management help maintain crop productivity and quality, ensuring that farmers can maximise their returns.

3. Reducing Environmental Impact: Using pesticides or other control methods unnecessarily can have adverse effects on the environment and non-target organisms. By applying control measures only when needed, at the ETL, farmers can reduce the environmental impact of pest or disease management practices.

4. Sustainable Agriculture: Adhering to the ETL promotes sustainable agriculture by balancing economic considerations with environmental stewardship. Sustainable pest or disease management practices are essential for maintaining agricultural productivity and preserving natural resources for future generations.

5. Resistance Management: Prolonged or indiscriminate use of pesticides can lead to the development of pest or disease resistance, making control measures less effective over time. By applying control at the ETL, farmers can help delay the development of resistance and maintain the efficacy of available control options.

6. Enhanced Decision-Making: The ETL provides a quantitative basis for decision-making in pest or disease management. By having a clear threshold to trigger control measures, farmers can make more informed and confident decisions to protect their crops effectively.

7. Improved Crop Health Monitoring: Monitoring pest or disease populations regularly to determine when they reach the ETL allows for better crop health surveillance. It facilitates early detection of potential problems, enabling prompt and targeted management interventions.

By implementing control tactics at the ETL, farmers can optimise pest or disease management, prevent economic losses, reduce environmental impact, promote sustainable agriculture, and enhance overall crop health and productivity.

Threshold level 
It is a term used in pest management to indicate the level of pest population or damage that requires some action to prevent further losses or harm. There are different types of threshold levels, depending on the criteria used to decide when to take action. 

Methods of Disease Control:

Disease control in agriculture involves the use of various strategies to manage and reduce the impact of plant diseases. These methods can be broadly categorized into several types, each with its unique approach to disease management. Here are the main methods of disease control:

1. Host Plant Resistance: Host plant resistance involves using plant varieties or cultivars that are naturally resistant or tolerant to specific diseases. Resistant plants can withstand infection or limit the spread of pathogens, reducing disease severity. Plant breeders develop disease-resistant varieties through careful selection and crossing of parent plants with desirable traits. Host plant resistance is a sustainable and cost-effective method of disease control.

2. Cultural Control: Cultural practices aim to create unfavourable conditions for disease development and spread. Some common cultural practices include crop rotation, planting disease-free seeds or transplants, and adjusting planting dates to avoid peak disease periods. Practices like pruning and proper spacing can improve air circulation and sunlight penetration, reducing humidity and disease pressure.

3. Mechanical Control: Mechanical methods involve physically removing or destroying diseased plant parts to limit pathogen spread. This includes pruning infected branches, removing infected leaves, and uprooting and disposing of severely affected plants. Mechanical control can be labour-intensive but can help contain disease outbreaks.

4. Physical Control: Physical control methods create barriers or modify the environment to prevent disease transmission. Examples include using mulches to suppress disease-carrying organisms, installing physical barriers (e.g., netting) to keep pests away, and using heat treatment to eliminate pathogens in planting materials.

5. Legislative Control: Legislative control involves implementing regulations and quarantine measures to prevent the introduction and spread of new diseases. Quarantining or restricting the movement of plants or plant materials from disease-infested areas helps contain disease outbreaks and protect disease-free regions.

6. Biological Control: Biological control uses beneficial organisms, such as predators, parasites, or pathogens, to target and control disease-causing organisms. For example, introducing predatory insects to feed on pests can reduce vector populations and disease transmission. Biological control is environmentally friendly and supports natural pest and disease regulation.

7. Chemical Control: Chemical control involves the use of pesticides, such as fungicides and bactericides, to manage disease outbreaks. These chemicals directly target the pathogens or suppress their growth. Properly timed and targeted use of pesticides can effectively control diseases, but excessive or indiscriminate use may lead to environmental concerns and pesticide resistance.

Disease control in agriculture relies on a combination of methods, each addressing specific aspects of disease management. Integrated Disease Management (IDM) emphasises the balanced and strategic use of these control methods to achieve effective disease control while promoting sustainability and minimising environmental impact. By integrating multiple approaches and considering factors like crop health, economic impact, and environmental considerations, farmers can implement a holistic and successful disease management strategy for their agricultural systems.

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