Economic Threshold of Infestation: How to Calculate It in the Field Before Deciding to Spray

Many spraying decisions in the field are driven by concern rather than calculation.
Seeing insects on plants often pushes some farmers to use an insecticide immediately, even though in many cases the infestation has not yet reached a level that causes real production loss.

Here comes the concept of the economic threshold of infestation, the scientific benchmark that determines when intervention becomes necessary and when waiting is the smarter decision.

Understanding this concept forms the critical link between accurate diagnosis and building an integrated crop protection program based on informed decisions rather than haste.

First: What Is the Economic Threshold of Infestation?

The economic threshold is the level of infestation at which the expected crop losses begin to exceed the cost of control.

In simple terms:

If the potential yield loss is greater than the cost of spraying → intervention is justified.
If it is lower → spraying is unnecessary.

This explains why not every presence of insects means you need to apply insecticides immediately.

Second: Why Do Many Farmers Misjudge the Economic Threshold?

A common mistake is confusing the presence of insects with the presence of real risk.

Finding three to five insects on a single plant does not necessarily mean the crop is threatened.
However, if infestation exceeds 20–30% of the plants, the situation begins to change.

Many cases of insecticide failure actually begin with unnecessary spraying, followed by selection pressure that later contributes to pest resistance.

Third: How Do You Calculate the Economic Threshold in the Field?

The calculation does not require complex equations, but organized steps:

1) Determine the Percentage of Infested Plants
Select 10 random sampling points within the field.
Inspect an equal number of plants at each point.
Calculate the overall infestation percentage.

2) Evaluate the Severity of Damage
Is the damage superficial, or does it affect growing tips or flowers?
Is the infestation stable, or is it doubling daily?

3) Estimate the Cost of Control
Pesticide price + labor cost + water cost + downtime.

4) Estimate the Potential Loss
Will the damage affect total yield?
Will it affect crop quality?

If the expected loss exceeds the cost of control → the economic threshold has been crossed.

Fourth: The Relationship Between the Economic Threshold and Pest Resistance

Spraying before reaching the economic threshold increases the number of pesticide applications unnecessarily.
With repeated use of the same active ingredient, pest resistance to pesticides may begin to develop.

Ignoring the economic threshold therefore not only increases costs but also accelerates the loss of control effectiveness.

Fifth: The Difference Between the Economic Threshold and the Critical Threshold

The economic threshold is not the same as the critical threshold.

The critical threshold is the level at which damage becomes nearly irreversible.

If intervention is delayed until the critical threshold is reached, losses have already occurred.

This is why regular monitoring is essential within integrated pest management systems.

Sixth: Factors That Influence the Economic Threshold

The economic threshold is not a fixed number; it varies depending on:

Crop type
Growth stage
Market value of the crop
Climatic conditions
Type of infestation (insect or fungal)

In some cases, damage may appear insect-related while the real cause involves a combination of insect and fungal infection.

Seventh: Common Mistakes in Applying the Concept

Preventive routine spraying without measurement
Increasing the dose out of concern
Ignoring plant growth stage
Failing to record infestation data

These mistakes turn pest control into a reactive action rather than strategic management.

Conclusion

The economic threshold of infestation represents the dividing line between scientific management and emotional decision-making in the field.
The goal is not simply to reduce spraying, but to ensure that every application is based on measurable justification.

When proper diagnosis, infestation assessment, and cost–loss evaluation are combined, the decision to use an insecticide becomes part of an integrated system rather than an emergency response.

Effective management does not begin with the pesticide container—it begins with numbers.