Economic Injury Level & When a Pest Is Worth Controlling
Decides on aphids
Enter control cost, crop value, damage per pest and efficacy to get the EIL and the economic threshold — so you spray only when the pest is worth controlling.
Set the injury level
Next: start control when pests reach the economic threshold (15), set below the EIL (18.8) so spraying acts before the damage outruns the cost.
The EIL is the pest density at which control cost equals the value of the damage prevented; the ET is a safety margin below it that gives time to act.
Economic injury level — key facts
- EIL
- cost ÷ (value × damage × efficacy)
- Economic threshold
- set below the EIL
- Typical ET
- ≈ 70–80% of EIL
- Why below EIL
- lead time before control acts
- Higher price
- lowers the EIL
- Lower efficacy
- raises the EIL
- Heart of
- integrated pest management
- Privacy
- Runs in your browser; nothing uploaded
Spray when it pays, not on the calendar
Not every pest is worth spraying. The economic injury level is the pest density at which the value of the damage prevented just equals the cost of control — below it, the pest costs less than the treatment; above it, action pays. The economic threshold, or action level, is deliberately set below the EIL so that control takes effect before the population grows past the injury level and losses outrun the cost. Together they are the heart of integrated pest management decisions.
This tool gives the EIL, the economic threshold, the control cost and the efficacy you assumed, from your crop value and damage per pest. Use it to turn scouting counts into a clear spray-or-wait decision, avoid calendar spraying, protect beneficial insects and slow resistance. Pair it with the Economic Threshold, Pest Degree-Day and Field Scouting calculators for a complete IPM workflow.
Spray only when it pays
Act above the injury level, wait below it.
Get the lead time right
Threshold sits below the EIL so control acts in time.
Cut wasted sprays
End calendar spraying and protect beneficials.
Slow resistance
Fewer needless treatments keep chemistry working.
Frequently Asked Questions
What is the economic injury level?+
The economic injury level (EIL) is the lowest pest density at which the value of the crop damage the pest would cause just equals the cost of controlling it. Below the EIL, damage costs less than the spray; above it, the pest is worth controlling. It is the central number in integrated pest management decisions — the point where action starts to pay.
How is the EIL calculated?+
EIL = control cost ÷ (crop value × damage per pest × control efficacy). In words: divide what control costs (per hectare or acre) by the value lost to each pest after allowing for how well the control works. The result is a pest density — pests per plant, per sample or per unit area — above which spraying returns more than it costs.
What is the economic threshold?+
The economic threshold (ET), or action threshold, is the pest density at which you should act — set below the EIL so control takes effect before the population grows past the injury level and losses outrun the cost. Pests breed and damage accumulates over the days between scouting and spray taking hold, so the ET builds in that lead time.
Why is the threshold set below the injury level?+
Because control is not instant. Between the moment you scout and the moment the spray works, the pest keeps feeding and multiplying. If you waited until the population hit the EIL, damage would overshoot it before control kicked in. Setting the economic threshold below the EIL — often around 70–80% of it — gives the lead time to stop losses at the right point.
What does control efficacy mean here?+
Efficacy is the share of the pest population the control actually kills or suppresses. No spray is 100% effective, so a treatment that kills 80% prevents only 80% of the potential damage. Lower efficacy raises the EIL — the pest must be denser before imperfect control pays for itself. Enter a realistic efficacy for your product and conditions.
How do I find the damage per pest?+
Damage per pest is the proportion of yield (or value) lost per pest per plant, per sample, or per unit area — drawn from research, extension guides or local trials for that pest and crop. It varies with crop stage: a feeding insect does far more harm at flowering or grain-fill than on a robust vegetative plant. Use the figure for your pest at the current stage.
Why use EIL and threshold instead of spraying on a schedule?+
Calendar spraying treats whether or not the pest is there, wasting money and chemicals and breeding resistance. EIL-based decisions spray only when the pest is dense enough to be worth controlling — the heart of IPM. It cuts unnecessary sprays, protects beneficial insects, slows resistance and usually lifts net returns over a season.
Do these levels change through the season?+
Yes. The EIL and threshold move with crop value (price and yield potential), control cost, the pest's damage potential at each crop stage, and efficacy. A higher crop price lowers the EIL — more is at stake, so a smaller pest population is worth controlling. Recalculate as prices, costs and crop stage change rather than treating one figure as fixed.
Does this work for any pest or crop?+
Yes — the EIL framework is universal. Enter the control cost, crop value, damage per pest and efficacy for your pest-and-crop combination, in whatever pest-density unit your scouting uses. The maths is the same for insects, mites or other pests; only the input figures change with the pest, crop and region.
Are the figures precise?+
They're sound decision figures. The real EIL depends on accurate damage-per-pest and efficacy values, which carry uncertainty, and on prices and costs that shift. Use the calculator with the best local figures, set the threshold below the EIL for lead time, and combine it with regular scouting — IPM is about better decisions, not perfect prediction.