How to Mix Pesticide Correctly in a 16-Litre Sprayer

The 16-litre knapsack sprayer is the workhorse of Indian crop protection. Yet the most important decision made with it – how much product goes into each tank – is often made with a bottle cap and a guess. This guide shows you how to get it right, using only the label and a little arithmetic.

A note before we start: we don't recommend any pesticide or dose. Always use a product approved for your crop and pest, at the dose on its label, or as advised by your Krishi Vigyan Kendra or agriculture officer.

Read the label carefully

Pesticide labels and leaflets in India list the crops and pests the product is approved for, the dose, the water volume, the waiting period before harvest, and safety precautions. The dose is usually given in one of two ways:

• Per litre of water – for example "2 ml/L" or "1 g/L".

• Per acre or per hectare – for example "300 ml in 200 L of water per acre".

The calculation depends on which one you have.

If the dose is per litre

This is the easy case:

Product per tank = Dose per litre × Tank size

For 2 ml/L in a 16 L tank: 2 × 16 = 32 ml per tank.

If the dose is per acre

You need one more number: how much water you actually spray on an acre.

Product per litre = Dose per acre ÷ Water per acre
Product per tank = Product per litre × Tank size

For 300 ml per acre in 200 L of water: 300 ÷ 200 = 1.5 ml per litre, so 24 ml per 16 L tank.

Here's the catch: if you actually spray 150 L per acre (because you walk faster or use a different nozzle), each tank covers more ground, and the crop gets only 75% of the intended dose. That's why calibration matters.

Calibrate your sprayer in 15 minutes

1. Mark out a known area in the field, say 10 m × 10 m = 100 m².

2. Fill the tank with a measured amount of clean water – 10 litres, for example.

3. Spray the marked area exactly as you normally would: same nozzle, pressure and walking speed.

4. Measure how much water is left. If 5 L remain, you used 5 L on 100 m².

5. Water per acre = water used ÷ area × 4,047. Here: 5 ÷ 100 × 4,047 = 202 L per acre.

Use that figure in the Pesticide Dilution Calculator and the Spray Tank Calculator.

How many tanks for your field?

Tank fills = Water per acre × Acres ÷ Tank size

At 200 L per acre and a 16 L tank, one acre takes 12.5 tank fills. Knowing this in advance helps you prepare enough product, arrange water, and mark the field so each tank covers the right strip.

Mixing safely, step by step

1. Wear gloves, a long-sleeved shirt, full trousers, eye protection and a mask.

2. Fill the tank about half full with clean water.

3. Measure the product with a measuring cylinder, marked cup or syringe – not a bottle cap.

4. Pour it in, then rinse the measuring cup into the tank.

5. Top up to the full volume and stir or shake well.

6. For powders (WP/WG formulations), make a smooth paste or pre-mix in a little water first.

If you plan to mix two products, check both labels for compatibility and do a small jar test first.

Common mistakes

• "A little extra for strength." It rarely improves control and increases cost, crop injury risk, residues and pest resistance.

• Using the same cap for every product. Caps vary in size, and doses vary between products.

• Spraying in wind or at midday. Drift wastes product and endangers people and neighbouring crops; heat increases evaporation and plant stress.

• Ignoring the waiting period. The pre-harvest interval on the label protects consumers – and your market.

After spraying

Triple-rinse empty containers and pour the rinse into the tank. Don't reuse containers for food or water. Wash your sprayer away from wells, ponds and channels, and wash yourself and your clothes thoroughly.