Plant Bacteriology

• Economic Threshold (ET) in Integrated Pest and Disease Management:
• Definition: The Economic Threshold (ET) is defined as the pest or disease population density at which active control measures must be initiated to prevent the increasing population from reaching the Economic Injury Level (EIL).
• Economic Basis: At the Economic Threshold, the marginal benefit gained from control equals or exceeds the cost of the control intervention—meaning the cost of controlling the disease is less than the economic value of the crop yield damage that would otherwise occur if no measures were implemented.
• nalysis: Option 3 accurately describes this fundamental cost-benefit threshold (Option 3).

Correct option: (3) The point where the cost of controlling the disease is less than the cost of the damage that would occur if no control measures were used

• Remote Sensing in Plant Disease Diagnosis:
• Spectral Bands Utilized:
• Visible Spectrum ($400-700\text{ nm}$): Healthy green vegetation strongly absorbs blue ($450\text{ nm}$) and red ($650\text{ nm}$) wavelengths for photosynthesis, reflecting green light. Diseased leaves lose chlorophyll, leading to increased reflectance in the red and blue regions.
• Near-Infrared Spectrum (NIR, $700-1100\text{ nm}$): Healthy internal leaf architecture (spongy mesophyll) scatters and reflects $\gt 50\%$ of incident NIR light. Pathogen invasion disrupts cell walls and collapses intercellular air spaces, drastically reducing NIR reflectance.
• Normalized Difference Vegetation Index (NDVI): Relies on combining reflectance in both visible and infrared regions ($NDVI = \frac{NIR - Red}{NIR + Red}$) to detect pre-visual and visual disease symptoms.
• Conclusion: Both visible and infrared wavelengths are critical (Option 3).

Correct option: (3) Both visible and infrared