Adjuvants – A Primer

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About Jason Deveau (Spray Guy)

Dr. Jason Deveau has been the OMAFRA Application Technology Specialist since '08. He researches and teaches methods to improve the safe, effective and efficient application of agricultural sprays in specialty crops, field crops and controlled environments. He is the co-administrator of Sprayers101, co-author of the Airblast101 Textbook, a slow cyclist and an even slower runner.

See all posts by Jason Deveau (Spray Guy).

We can always count on receiving regular questions about tank mixes but in recent years we’re hearing more about adjuvants.

Many pesticides are already formulated with a variety of adjuvants. Perhaps they are intended to improve shelf-stability, or mixing and/or product performance. A pesticide label may specify a particular name brand or generalize a category of adjuvant. In this case, they do not come pre-formulated because they might impact product stability, increase bulk and increase expense. In Canada, the grower is free to use any adjuvant in that category provided it is registered for use on the crop and in combination with the pesticide being applied.

But there are many adjuvants that are not specifically required on the product label and their claims of improved pesticide performance make it tempting to throw them in the mix. Adjuvants can do everything from masking pesticide odor, conditioning carrier water and reducing drift (utility adjuvants) to improving the degree of contact between droplets and the plant surface, or enhancing product uptake or rainfastness (activator adjuvants). How do you know which, if any, to use?

The following video presentation was recorded for a 2021 adjuvant conference in Argentina. It’s a primer to introduce what adjuvants are and why we might consider using them. You’ll note that I speak slowly during the presentation – that’s because I believe it was being translated and I wanted to make that process as easy as possible. Also, I think I said captan was an insecticide – in fact it’s a fungicide.

Surfactants (SURFace ACTive agENTS) are activator adjuvants and are the products most often added to tank mixes as afterthoughts. This video was filmed in 2015. It was intended as a quick example of how a sticker reduces runoff and how a penetrant can help a product pass through a waxy plant surface. Special thanks to former OMAFRA summer student, Victoria Radauskas for filming this video.

However tempting, be sure to read the label of each tank mix partner and seek advice from the dealer or manufacturer before using them. You don’t want to create physical incompatibilities in the tank. A jar test will tell you more about that. Perhaps worse, chemical incompatibilities are not immediately obvious but they can reduce product efficacy or result in phytotoxicity that might damage your crop. Consider trialing the mix on a few plants to confirm there are no undesirable biological impacts.

Here are a few general warnings when using surfactants in horticultural crops:

  • Do not use penetrants (including oils) with copper, sulphur or captan fungicides.
  • Do not use penetrants with contact or surface pesticides.
  • Stickers may impede the movement of systemic products.
  • Stickers may prevent redistribution to newly emerging leaves early in the growing season (but they may be desirable during wet springs).
  • Deposition utility modifiers may negatively affect canopy penetration when employing multi row or alternate row traffic patterns.
  • Spreaders are more likely to incur runoff so adjust volumes accordingly.

When you’ve done your due-diligence you’ll be more likely to enjoy the potential benefits of adjuvants.

And, just in case you want more, here’s a 2022 interview from Real Agriculture’s “The Agronomists” featuring Tom Wolf of Agrimetrix, and Greg Dahl of Winfield United. For the adjuvant-related part of the conversation, you can pan ahead to the six-minute mark.

Finally, here are two excellent resources you can download:

The GRDC’s Adjuvants Booklet

Purdue’s “Adjuvants and the Power of the Spray Droplet” Booklet