Tank Mixing and Pesticide Compatibility – “The Jar Test”

Dr. Jason S.T. Deveau, Application Technology Specialist, OMAF and MRA; James D. Reiss, VP Ag Chem, Precision Laboratories, LLC; Helmut Spieser, Agricultural Engineer, OMAF and MRA

Are you considering a new tank mix this year? Perhaps two new fungicides, or an adjuvant you want to try? Be sure you know what you’re doing before you risk an untested tank mix. Users of commercial class pest control products for crop protection or vegetation management are permitted to apply unlabelled tank mixes of registered pest control products as long as:

• each partner is registered for use in Canada 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.

The order in which you add each product to the tank or inductor is critical. Making sure you have the right mix, in the right order, is made easier with the free app from Precision Laboratories (www.mixtankapp.com) which works on Android and iPhone/iPad systems.

At the start-up screen, select “Mix Guide” (see Figure 1). Then, select the category of the product you wish to tank mix (see Figure 2) and then select the product(s) from the alphabetized list. The app analyzes your selections and suggests the best order to add them to the tank. Note that these are US products, which means they may have different names in Canada, if they are registered at all. The app has other appealing features you can explore, such as saving your mixes for future reference, and accessing instructional videos.

Always check the product labels for information on compatibility of spray materials. “Compatibility” refers to the physical and/or chemical compatibility of two or more products in a solution. If you are concerned, you should perform a jar test. Always wear personal protective equipment and do it 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 Table 1, 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 (see Figures 3 and 4 for examples of physical incompatibility).
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).

Table 1 – Tank mix order for performing a pesticide compatibility test

Order	Ingredient	Quantity for 500 ml or g of product labeled for 1,000 L of final spray volume
1.	Compatibility agents	5 ml (1 teaspoon)
2.	Water-soluble packets, wettable powdersand dry flowables	15 grams (1 tablespoon)
3.	Liquid drift retardants	5 ml (1 teaspoon)
4.	Liquid concentrates, micro-emulsionsand 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)

Commercial compatibility kits are available, such as the kit from Precision Laboratories. This kit contains three plastic “jars” and five disposable micropipettes (see Figure 5). 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. These kits can be purchased for ~$20.00 (including delivery) by calling 1.800.323.6280.

Remember: 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.