Tank Mixing Order and the “Jar Test”

When it comes to reliable information on tank mixing, there are many resources available. In 2018 Purdue University published an excellent and comprehensive manual: “Avoid Tank Mixing Errors”. Download or order a copy.

The label is always the first point of reference, and it should be obeyed even if it contradicts everything that follows in this article. Search the label for instructions on which tank mix partners are required, or which are prohibited. If you are considering mixing partners not listed on the label, beware that local regulations may or may not permit you to do so.

In Canada, users of commercial class pest control products for crop protection or vegetation management are permitted to apply unlabeled tank mixes of registered pest control products as long as:

  • Each partner is registered for use on the crop.
  • The tank mix only includes an adjuvant when specifically required by one of the mix partners.
  • The application timing of each partner is compatible with crop and pest staging.
  • Each partner is used according to the product label.
  • No partner is specifically excluded on any other partner label.

Odds are you are not inventing a new tank-mix and someone else has already tried it, so: 

  • consult your chemical representative. They know their products best and want to see you succeed and may have information that is not on the product label;
  • consult local government or academic extension programs for an unbiased opinion;
  • enlist the help of a professional crop advisor.

Be wary of advice obtained from other growers at coffee shops.

If you are considering a tank mix, it’s best not to exceed three tank partners. The more you put in, the more likely formulated adjuvants and inerts become incompatible. “Compatibility” in this case means that mixing products will not cause a chemical problem (e.g. affect efficacy) or a physical problem (e.g. products gel, layer or fall out of suspension).

A gelatinous mess made by using an inductor as a mixing vat for incompatible products. Photo Credit – Dr. J. Reiss, Illinois.
An example of physical incompatibility in the sprayer tank. Photo Credit – Dr. J. Reiss, Illinois.

W.A.L.E.S. or W.A.M.L.E.G.S.?

Labelled or unlabeled, the order in which you add tank mix partners to the tank, or inductor, is critical. The acronym W.A.L.E.S. (Wettable powders, Agitate, Liquid flowables, Emulsifiable concentrates, Surfactants) has been the historic guideline, and many feel it is still adequate.

However, as we combat resistance with multiple modes of action and use today’s more chemically-complex products, BASF has suggested the acronym W.A.M.L.E.G.S. to include microencapsulated suspensions and high-load glyphosates. Fill the tank half-full of water (or 3/4 full of fertilizer – UAN is very different from water) to allow products to properly hydrate, and with the agitation on, follow this order:

Generally, true soluble liquids don’t have much impact on mixing sequence. They can be added early, or late with other SL’s. It seems the biggest issue to compatibility is where dry formulations and EC’s are added in the mixing sequence. In the case of growers adding microelectronics like sulfur (e.g. ATS) to nitrogen-based formulations (e.g. UAN) many recommend caution and have suggested adding them at the very end of the mixing order. Depending on the amount of ATS, we have seen variable success.

Less common, what about tank mixing biologicals such as biostimulants? Assuming that most of these materials are formulated as soluble liquids (not an EC or SC), add them at the end of the mixing procedure. If they are formulated as dry (WDG, WP, etc.) then they would go in to the spray preparation very early in the mixing sequence. When it comes to living organisms with true biologicals, an additional consideration of the tank solution pH needs to be considered.  Biologicals prefer a pH around 7.  Rhizobia and Mycorrhizal Fungi are especially sensitive to lower pH’s.

Want to know more about water chemistry? In April, 2016, Les Henry published an article in Grainnews called “The Coles Notes of Water Chemistry“. It’s well worth the read. You can also read about pH and water hardness here.

Steps for performing a jar test

Making sure you have compatible tank mix partners, in the right order, is made easier with free smartphone apps from companies like AgChemExpert, DuPont, or Precision Laboratories. But no app replaces hands-on experience. If you are concerned, you should perform a jar test.

Always wear personal protective equipment (PPE) when performing a jar test. Do so in a safe and ventilated area, away from sources of ignition.

  1. Measure 500 ml of water into a one litre glass jar. This should be the same water you would fill a spray tank with.
  2. Add ingredients according to the label or W.A.M.L.E.G.S., stirring after each addition.
  3. Let the solution stand in a ventilated area for 15 minutes and observe the results. If the mixture is giving off heat, these ingredients are not compatible. If gel or scum forms or solids settle to the bottom (except for the wettable powders) then the mixture is likely not compatible.
  4. If no signs of physical incompatibility appear, test the mixture using a spray bottle on a small area where it is to be applied. Look for phytotoxic indications, such as plant damage, and monitor efficacy (which is hard to do unless you actually fill the sprayer and try it on a few plants).

Compatibility Kits

Commercial compatibility kits are available from most agrichemical suppliers, such as the one from Precision Laboratories (below). They contain a few plastic “jars” and disposable micropipettes. By following the instructions included with the kit, you can easily reduce large labelled volumes (such as 1.0 kilogram of product in 500.0 litres) of multiple products to small volumes at the same ratio. In this case we assume the final volume would have been 1,000 L, and so we reduce all the quantities accordingly to get 500 ml:

  1. Compatibility agents 5 ml (1 teaspoon)
  2. Water-soluble packets, wettable powders
    and dry flowables 15 grams (1 tablespoon)
  3. Liquid drift retardants 5 ml (1 teaspoon)
  4. Liquid concentrates, micro-emulsions
    and suspension concentrates 5 ml (1 teaspoon)
  5. Emulsifiable concentrates 5 ml (1 teaspoon)
  6. Water-soluble concentrates or solutions 5 ml (1 teaspoon)
  7. Remaining adjuvants and surfactants 5 ml (1 teaspoon)
Contents of a commercially-available compatibility test kit.
Contents of a commercially-available compatibility test kit.

A compatibility test will only reveal physical incompatibility between products in a tank mix – they will not reveal any other form of antagonism, such as products inactivating one another, or the potential for phytotoxicity. The only way to know for sure is to apply the mix to a few test plants and keep an eye on them over the season.

What to do if you have accidentally created a mess

An unfortunate grower posed the following question:

I mixed up a batch of MCPA 500 A and Glyphosate @ 3/4REL, but then got delayed on application with a stuck drill. I came back to the sprayer and found a nasty chemical precipitate – like waxy chunks. Agitation didn’t break them down. I dumped the tank out as I didn’t want to pump it through the booms. How do I clean up the chunks in the system?

We forwarded the question to a few ag chemists, and received this response:

Wearing appropriate personal protective equipment, physically remove the “chunky” material. A lot of time can be wasted (and rinsate water created) by experimenting with various concoctions, but if you do choose to try a compatibility agent, first try it in a mason jar. If it works to dissolve the material, it can be added to the tank with water and agitated. If not, you are down to manual cleaning: hot water under pressure.

And so, the best advice is to not put yourself in this position to begin with. Don’t make mixing decisions at the inductor bowl – make them before ordering product.

Thanks to Eric Spandl (Land o Lakes), Mike Cowbrough (OMAFRA), Jim Reiss (Precision Laboratories) and Rob Miller (BASF) for informing this article.

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