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Mixing your spray solution properly is important - and it is a task that needs careful thought, planning, and preparation. The quality of the water you use and the extent of agitation are important factors to consider, and if you are combining more than one agrichemical in the same tank mix, you introduce another source of potential problems.

Mixing site

Whether you are using a temporary or permanent mixing site, check your mixing site has the following features:

  • Far enough from plants and animals to prevent damage from dusts or vapours
  • Far enough from any drain, well or water body to prevent contamination
  • Good ventilation and lighting
  • Uncluttered area free from interference, so there is no confusion or distraction
  • A level surface to enable accurate measurement.
  • Good supply of clean water for mixing and washing. You may need to bring water with you. If using water from a stream or lake, ensure there is no possibility of contamination by using a backflow preventer such as a one way valve.
  • Access to a suitable emergency spill kit. Ideally your mixing site should have an impervious surface to avoid soil contamination.
  • Access to first aid kit.

Measuring and mixing procedures

Measuring and mixing agrichemicals accurately is a key requirement of safe and effective agrichemical use. Here is the way to mix correctly:

  1. Ensure you use the correct PPE. Remember that when you are handling concentrated agrichemicals this is the riskiest time for you and the environment – you may wish to wear additional PPE such as an apron or eyewear when mixing, along with the PPE you will wear for application.
  2. Check the spray equipment is clean. If using a different agrichemical to the one last used, check the equipment has been decontaminated.
  3. Check you have the correct agrichemical.
  4. Read the label for the recommended application rate and any product specific information about mixing.
  5. Calculate the amount of spray mixture required for the task then calculate how much spray concentrate is needed for the tank.
  6. Add about half the required water to the spray tank. Ensure the water is clean.
  7. Choose an appropriate measuring jug. Rule of thumb: the amount to be measured should be at least quarter of container volume and match the gradations available. For example, if you need to measure 90ml then use a 120ml or 250ml jug not a 1 litre jug.
  8. Accurately measure the concentrate (place measuring jug on a level surface) and add it to the spray tank. Ensure caps and lids are replaced on containers as soon as possible.
  9. Triple-rinse your measuring containers as you go and add the rinsate to the spray tank – do not tip the rinsate out on the ground or down a drain. Triple rinse the agrichemical container if you empty it, adding the rinsate the spray tank.
  10. Top up the spray tank with clean water to the required level.
  11. Return agrichemical containers to the store before starting spraying.

If you are carrying agrichemical away from the agrichemical for mixing at the application site, you may decant the agrichemical into smaller, more portable containers.  If you do this, you must label the container with the product name and any hazard pictograms or statements such as ECOTOXIC.   You must also carry with you a full label or a HazNote with emergency information in case it is required.

A good way to manage this is to buy a number of small containers of the agrichemical and then when they are empty (but still with labels attached), refill with the same product from the larger containers. 

Combining agrichemicals

Two or more agrichemicals are frequently combined in a spray tank to control different pests and diseases with a single application. While reducing application costs, this practice can lead to significant application and efficacy problems:

  • Effectiveness of one or both products may be reduced
  • Different chemical compounds and formulations may interact resulting in precipitation or clumping
  • Combinations of chemicals may damage crop tissue
  • Chemicals may not 'stick' to the crop due to the combined effect of wetters in each product
  • Excessive residues may occur in crop tissue or soils.

The chance of one or more of these problems occurring increases with the number of products involved.

To guard against any of these outcomes you must read the label of each agrichemical you want to mix together. The labels will indicate if two products can be mixed together, and show the order in which they need to be mixed.

Proper order for tank mixing

Formulations of different active ingredients can in some cases be mixed before use. However, this should only be done if it is known that the two formulations are compatible and that there will be no adverse effects due to the mixing of the formulations.

Whether you are mixing one or more agrichemicals, carefully follow the mixing instructions on the label(s). It often describes the recommended mixing order and gives other important mixing or agitation instructions.

It is usual to fill the tank one-quarter to one-half full with water and begin agitation. If you need to add a compatibility, buffering, or defoaming agent, these products should be added before the other products. If you are using a drift control additive, always consult the label - some are added very early, while some are added nearly last.

In general, if more than one agrichemical is going to be added to a tank then they should be added in the 'WALES' sequence:

W Wettable powders then dry flowables
A Agitate then add adjuvants such as buffers
L Liquid and soluble products
E Emulsifiable concentrates
S Surfactants


Agitation and mixing of spray mixtures

Agitate your tank to ensure an even distribution of the active ingredients in the spray solution and to prevent settling of particulate products. Without agitation, it is possible that your spray solution will be too concentrated at the beginning of spraying and too diluted by the end.

Ensure a uniform spray mixture at all times by:

  • Agitating during loading and mixing
  • Keeping the mixture agitated during application
  • Turning the PTO and pump on when driving to the crop or stopping for a break
  • Make sure that agitator is designed to move water in one direction and ‘sweep' the bottom of the tank
  • Do not allow the mixture to stand overnight without agitation – if possible apply all of a tank mixture in one day.