Economic Threshold Calculator & Should You Spray?
Decides on spraying
“Power users leave notes. That is how you can tell the power users.
Spray only when it pays — compare your scouted pest density to the economic threshold and weigh the damage prevented against the spray cost for a clear spray / monitor / hold decision.
Enter your pest & crop
Next: scout fields regularly, rotate insecticide modes of action to slow resistance, and spray only when both conditions are met — pest density at/above the ETL and the value of damage prevented beats the control cost.
ETL is the pest density at which control cost = damage prevented; scout fields, don't spray by calendar. Estimates only — confirm with local advisory thresholds.
Economic threshold — key facts
- Spray when
- pest ≥ ETL and benefit > cost
- ETL
- ≈ 70–80% of the injury level
- EIL
- where damage cost = control cost
- Damage prevented
- yield × price × loss% × efficacy
- Benefit-cost
- damage prevented ÷ cost
- Scout
- several random points, averaged
- IPM rule
- thresholds, not the calendar
- Privacy
- Runs in your browser; nothing uploaded
Spray when it pays — not by the calendar
Routine calendar spraying is expensive and self-defeating: it wastes chemical when pests are below damaging levels, wipes out the natural enemies that keep pests in check, and accelerates resistance. The smarter rule, at the heart of integrated pest management, is the economic threshold — act only when the scouted pest density reaches the level that justifies control, and only when the value of damage prevented beats the cost of spraying.
This tool makes that decision concrete. Enter your scouted pest count, the published ETL for the pest, and your control cost, expected yield, price and likely loss, and it returns a clear spray / monitor / hold verdict plus the benefit-cost ratio and net benefit. Scout fields regularly, rotate modes of action, and lean on resistant varieties and biocontrol. Pair it with the Spray & Tank Mix and Pre-Harvest Interval tools when a spray is justified.
Spray only when needed
A clear over/under-threshold call from your scouted count.
Check it pays
Benefit-cost ratio stops sprays that cost more than they save.
Cut input costs
Skip unnecessary sprays, saving chemical, fuel and labour.
Protect your chemistry
Fewer, well-timed sprays slow resistance and spare beneficials.
Frequently Asked Questions
What is the economic threshold level (ETL)?+
The ETL (or action threshold) is the pest density at which you should act to prevent the population reaching the level that causes economic damage. Spray at or above the ETL; hold below it. It's the cornerstone of integrated pest management (IPM) — spraying by scouting, not by calendar.
How do I decide whether to spray?+
Two conditions: the scouted pest density must reach the ETL, AND the value of damage prevented must exceed the control cost. This tool checks both — it flags whether you're over threshold and computes the benefit-cost ratio, giving a clear spray, monitor or hold decision.
What is the difference between ETL and economic injury level?+
The economic injury level (EIL) is where the cost of damage equals the cost of control — the break-even pest density. The ETL is set a little below the EIL (often 70–80%) so you act before damage actually reaches the break-even point, allowing time for the spray to work.
How do I find the ETL for my pest?+
ETLs are published by agricultural universities and extension services for each crop-pest pair (e.g. so many larvae per plant, or % leaf damage). Use your local recommendation and enter it here. The tool then compares your scouted count to it and adds the economics for your costs and prices.
How should I scout for pests?+
Sample several spots across the field at random (not just the edges or worst patch), count the pest per plant, per leaf or per sweep as your ETL is defined, and average them. Scout regularly — weekly or twice-weekly in the susceptible stage — so you catch populations as they approach the ETL.
Why not just spray on a schedule?+
Calendar spraying wastes money when pests are below threshold, kills natural enemies, speeds up resistance, and adds residues — often without improving yield. Threshold-based spraying treats only when it pays, protecting both your margin and the long-term effectiveness of your chemistry.
What is the benefit-cost ratio here?+
It's the value of damage prevented divided by the control cost. Above 1 means spraying returns more than it costs; the higher, the better. The tool multiplies your expected yield, price and the loss avoided (adjusted for how effective control is) and divides by the spray cost.
What if I'm over threshold but it doesn't pay?+
That can happen with a cheap crop, low expected loss or expensive control — the tool flags it as 'over threshold but control may not pay'. Re-check your figures, consider a cheaper control, or accept some damage. Spraying that costs more than it saves destroys value.
Does control efficacy matter?+
Yes — no spray is 100% effective. If control only prevents 80% of the potential loss, the damage prevented (and the benefit) is scaled down accordingly. Enter a realistic efficacy; over-stating it makes marginal sprays look better than they are.
How does this support IPM?+
It operationalises the core IPM rule — act on thresholds, not the calendar — and forces an economic check before spraying. Combine it with scouting, resistant varieties, biological control and rotating modes of action to keep pests below the ETL with the fewest, best-timed sprays.
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