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How to Mix Spray to the Label Rate
Manesh Jayawardhana
CIO & Co-founder
The label says 2.5 litres per hectare. Your tank holds 200 litres. How much concentrate goes in?
You can’t answer that without knowing how much area a tankful covers, and that depends on your sprayer’s output rate — which is a number you have to measure and most people assume.
Two rates, and only one is on the label
The label rate is concentrate per hectare. It’s a legal instruction, not a recommendation, and it’s set for efficacy, residue limits and environmental safety.
Your output rate is water volume per hectare, determined by your nozzles, pressure and forward speed. It’s a property of your sprayer, not of the product.
The concentrate per tank follows from both:
area per tank = tank volume ÷ output rate
concentrate per tank = label rate × area per tank
A 200 L tank at 250 L/ha covers 0.8 ha. At a 2.5 L/ha label rate, that tank needs 2.0 L of concentrate.
Change the output rate and the concentrate per tank changes with it — same label rate, different mix. Which is why a neighbour’s mixing figure is useless to you unless your sprayers are calibrated identically.
Calibration is the step that gets skipped
Output rate isn’t the specification figure. Nozzle wear increases flow over time, sometimes substantially — a worn nozzle can deliver noticeably more than its rating, and the wear is invisible.
Pressure varies. Forward speed varies, especially with a tractor operated by feel rather than by a speed readout.
To calibrate: spray a measured area with water, measure how much was used, and divide. Repeat after changing nozzles, and check periodically — annually at minimum, more often in heavy use.
The catch test also reveals uneven output between nozzles, which no mixing calculation compensates for. A boom where one nozzle delivers substantially more than its neighbours is over-applying in a strip and under-applying elsewhere, which is both a residue risk and an efficacy problem.
| Variable | Set by | Check |
|---|---|---|
| Label rate | The product label | Read it every time |
| Output rate (L/ha) | Nozzles, pressure, speed | Calibrate |
| Concentrate per tank | Both of the above | Recalculate if either changes |
The label is a legal document
Worth stating plainly: in most jurisdictions, applying a plant protection product other than in accordance with its label is an offence.
That covers the rate, the crop, the growth stage, the maximum number of applications, buffer zones near water, and the harvest interval. Exceeding the rate isn’t a cautious over-application — it’s a breach, with consequences ranging from crop damage and residue violations to prosecution and loss of certification.
Under-applying has its own problem: sub-lethal doses select for resistance, which is how effective products stop working.
Common mistakes to avoid
- Using the sprayer’s specification output rather than a measured one.
- Mixing a full tank when the remaining area needs half — surplus spray is regulated waste and awkward to dispose of.
- Adding concentrate before part-filling with water, which can cause it to stick in the tank bottom.
- Ignoring nozzle wear because output “looks fine”.
- Assuming a rate from a different product, crop or region applies.
How to do it with Pesticide Dilution Calculator
The Pesticide Dilution Calculator ties concentrate to your calibrated output.
- Read the label rate — it’s the legal instruction.
- Enter your measured output rate, not the specification.
- Set the area to treat and the tank volume.
- Mix only what the remaining area needs.
Your national regulator publishes the rules on application and record-keeping. Other agricultural calculators are in the tools directory.
Frequently asked questions
Why does sprayer output matter if the label rate is per hectare?
Because the concentrate is dosed per hectare while the water is dosed per tank. Get the output rate wrong and you apply the right amount of water with the wrong amount of active ingredient.
How do I calibrate a sprayer?
Spray a measured area with water, measure the volume used, and divide. Nozzle wear changes output over time, so it needs re-checking rather than assuming the specification.
Is exceeding the label rate ever acceptable?
No. Label rates are legally binding in most jurisdictions, set for efficacy, residue limits and environmental safety. Exceeding them risks crop damage, residue violations and prosecution.
Final thought
Calibrate before you mix. The label rate is fixed and the output rate is yours — and it’s the one that’s probably drifted since you last checked.