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Pest Patrol

A handy acronym can help you remember what gets added during tank mixing

What is the proper order for tank mixing pesticides?

If a tank mix is listed on a pesticide label, there will be specific mixing instructions. However, the Pest Management Regulatory Agency (PMRA) does permit the application of unlabelled tank mixtures if the pesticides are registered on the target crop and are being applied within their labelled use pattern. When you are considering an unlabelled tank mix, it is best to consult the manufacturer of all products involved, as they may have experience with the mixture.

Since the pesticide label won’t provide any mixing instructions for unlabelled tank mixtures, the “WALES” method of pesticide mixing is a reasonable way to minimize any mixing issues. A compatibility test or “jar test” should be performed first so that you can identify any potential problems. Test kits are available through Precision Laboratories but you could also make your own with a glass jar and syringes to measure out pesticide amounts.

The “WALES” method of pesticide mixing is just an acronym to help you remember the preferred order, although personally I can never remember it, and that is why I will provide it below.

First, fill the spray tank about halfway (some operators swear by three-quarters full) and begin agitation. Then add:

Wettable powders and water-dispersible granules (basically any herbicide with a “dry” formulation goes first).
Agitate tank mix thoroughly (alright, you caught me, the agitator is already on as per our first step, but it wouldn’t make a good acronym if this point was “wait until the wettable powder is dissolved before adding anything else.”
Liquid flowables and suspensions.
Emulsifiable concentrate formulations.

Have a question you want answered?
#PestPatrol on to @cowbrough or email Mike at
[email protected].

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