When it comes to reliable information on tank mixing, there are many resources available. Learn more by downloading Purdue Universities’ 2018 publication: “Avoid Tank Mixing Errors“.The label is, of course, your first point of reference. You can also consult a trusted point-of-sale or agrichemical representative: they know their products best and want to see you succeed. They may also have information that never makes it onto the product label. You can also look to local government or academic extension programs for an unbiased opinion, or consider enlisting the help of a professional crop advisor.
Beware advice obtained from other growers at coffee shops.
W.A.L.E.S. becomes W.A.M.L.E.G.S.
If you are considering a new tank mix, it’s best not to exceed three tank partners. The more you put in, the more likely active ingredients and formulated adjuvants will be incompatible. “Compatibility” in this case means that mixing products will not cause a chemical problem (e.g. affect product efficacy) or a physical problem (e.g. products gel or fall out of suspension).
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.
Even if they are compatible, the order in which you add each product to the tank, or inductor, is critical. Beware the old acronym W.A.L.E.S. (Wettable powders, Agitate, Liquid flowables, Emulsifiable concentrates, Surfactants), which is becoming increasingly inadequate for today’s formulated products. Some extension specialists have condemned it outright. BASF suggests a new acronym: W.A.M.L.E.G.S. Fill the tank half-full of 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 Soluble Liquids (e.g. Roundup, Clarity, Banvel). The biggest issue to compatibility is where dry formulations and EC’s are added in the mixing sequence.
And what about tank mixing biologicals such as biostimulants and soil amendments? 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.
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.
Steps for performing 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.
- Measure 500 ml of water into a one litre glass jar. This should be the same water you would fill a spray tank with.
- Add ingredients according to the “Tank mix order” list (below), stirring after each addition.
- 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 (see Figures 3 and 4 for examples of physical incompatibility).
- 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).
Tank mix order
Remember W.A.M.L.E.G.S? Here’s how to interpret it for the jar test based on advice from Precision Labs. 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:
- Compatibility agents 5 ml (1 teaspoon)
- Water-soluble packets, wettable powders
and dry flowables 15 grams (1 tablespoon)
- Liquid drift retardants 5 ml (1 teaspoon)
- Liquid concentrates, micro-emulsions
and suspension concentrates 5 ml (1 teaspoon)
- Emulsifiable concentrates 5 ml (1 teaspoon)
- Water-soluble concentrates or solutions 5 ml (1 teaspoon)
- Remaining adjuvants and surfactants 5 ml (1 teaspoon)
Commercial compatibility kits are available from most agrichemical suppliers. 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.
Adding pesticide to the sprayer may not be straight-forward. Many airblast operators, for example, place dissolvable pouches in the basket so they can be broken up by the hydraulic return, or the fill water. But fill water often splatters out of the basket, and the bags can “puff” open, releasing product into the air. This creates unnecessary contamination and operator exposure. Because of this, I often recommend the operator remove the basket and add the pouches to a half-full tank with the agitator on, then give the pesticide time to dissolve or suspend.
However, I have heard of a situation where adding pouches to a half-full tank with the hydraulic and mechanical agitator operating might cause problems. In this case, the pump sucked in the partially dissolved bag coating and collapsing the inner screen because the pump was starved for water and created a lot of suction. The operator had to rebuild the pump because the Viton seals burned out rapidly without water. This operator now premixes slurry, or adds pouches to the basket while standing upwind and away from potential splatter.
Choose the safest and most effective method for your situation.
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.
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.
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?
I forwarded the question to a few colleges, 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.
Thanks to Eric Spandl (Land o Lakes), Jim Reiss (Precision Laboratories) and Rob Miller (BASF) for informing this article.