Feature image copyright belongs to Agencia Europea de Medio Ambiente

Adjuvants and herbicides know each other nearly as well as a couple at their 50th wedding anniversary party. Adjuvants and corn and soybean fungicides, though, mimic a newlywed couple — sometimes clicking along in unison and other times in confusion.

“There has been lots of good, hard research done with herbicide adjuvants but not a lot done on adjuvants for fungicides,” says Johnnie Roberts, director of formulation development and chemical support for Helena Chemical Company. That’s changing, though, as 2005’s soybean rust scare prompted more corn and soybean fungicide adjuvant research.

Entering the world of fungicide adjuvants is a bit like entering the Wild West. “I tell people that, in a sense, there is a lack of control in this industry,” says Bob Wolf, Kansas State University (KSU) Extension agricultural engineer. “EPA has no stipulation for these kind of products, only those with active ingredients.” Most states also do not regulate them.

Wolf says there have been industry strides made in improving product claims. Still, he’s had cases when water has had lower drift occurring than when drift-reducing adjuvants were added in KSU research trials. He recommends researching unbiased third-party research trials and adopting use on part of your farm before using them across your acres.

“Ask for data and independent research trials,” adds Jim Reiss, agricultural business vice president for Precision Laboratories. “University data is very credible.”

When they work as claimed, adjuvants enhance fungicide effectiveness. “A recommended adjuvant will spread the fungicide across the plant and make for better coverage,” says Nick Fassler, market development manager for BASF, manufacturer of Headline fungicide.

So what should you look for in an adjuvant?

“Saying you need an adjuvant is like saying you need a detergent,” says John Garr II, GarrCo Products president.

There are different types of detergents, just as there are different types of adjuvants. Some minimize drift. Some help spread fungicides across the leaf. Others aid fungicide leaf penetration. Adjuvant choice also differs between ground and aerial applications. Aerial applications use a low amount of water carrier, often 2 to 3 gallons per acre. Ground applications can contain 10 gallons per acre or more.

Less water means finer particles. “They mimic a mist of Windex,” says Garr. “Small droplets don’t get down in the canopy. Bigger droplets actually go farther into the canopy and on the leaves.”

Ideal fungicide droplet size ranges between 200 to 300 microns. (As a comparison, 100 microns is the diameter of a human hair.) Droplets smaller than this — including those mist-like ones prone to occur in aerial applications — drift. A drift-retardant adjuvant (such as one containing a polyacrylamide polymer) can slice off-target movement by 50% to 80%.

Aerial and ground applications can also drive other adjuvant choice. “Aerial application has issues about deposition; ground has issue about coverage,” says Roberts.

The distance aerially applied fungicides travel from boom to crop boosts evaporation potential. Also boosting the likelihood of evaporation is the minimal amount of water applied by plane.

“With aerial application, it is important for adjuvants to reduce evaporation to achieve deposition,” says Roberts.

Crop oil concentrate adjuvants are one way to whip evaporation.

“They also will penetrate a waxy or woody (leaf) surface and get the product into the plant a little quicker,” says Doug John, director of sales and marketing for Kalo.

When satisfactory deposition occurs, satisfactory coverage also results, says Roberts.

The higher water volume of ground application eases deposition concerns. However, fungicide diffused over more water volume puts optimum coverage into question. These concerns can be eased by a nonionic surfactant.

“Surfactant stands for surface active agent,” says John. “Surfactants essentially take a drop of water (and fungicide) and evenly spread it across the leaf. It makes the spray solution wetter and improves coverage and uptake.”

A fungicide’s label will typically recommend some type of nonionic surfactant or crop oil concentrate. Still, this hinges on fungicide type. Strobilurin fungicides (such as Headline and Quadris) can be used with a number of adjuvants. Not so with triazole fungicides, which are curative products applied after onset of disease.

“Triazoles can be sensitive to adjuvants from a phytotoxicity standpoint,” says Tom Pekarek, specialty department manager at United Suppliers, Inc. If triazole fungicide labels do permit an adjuvant, it most likely will be a drift-reduction agent. Fungicides containing a mix of strobilurin and triazole fungicides often can be used with more adjuvants, he adds.

Multipurpose adjuvants are available, such as one that combines drift-retardant capacity with penetration capacity. Convenience and no mixing are powerful perks for these products.

Still, you do sacrifice performance, as adjuvants with a specific purpose perform better than multimode ones. “They might be decent at a lot of different things but not great at one certain thing,” says Garr.

Depending upon product and application selection, cost widely varies. Payback hinges upon price and product performance.

“Suppose you have 10 gallons of water per acre in a fungicide and water mix,” says Garr. “You lose 10% (1 gallon) to drift and evaporation. But with a deposition agent, you recover 60% of that back. Instead of losing 1 gallon of the mix, you lose just 0.4 gallon.

So how much is that 0.6 gallon worth? “With a $15 application cost ($1.50 per gallon), you’ll have saved 90 cents of product,” says Garr. “If it cost you 50 cents to add the deposition agent, you’ll have made money.”

Timing is key for adjuvant effectiveness.

Purdue University research in 2008 and 2009 conducted by Purdue University scientists Bob Nielsen, Corey Gerber, and Kiersten Wise determined pretassel fungicide applications with nonionic surfactant or crop oil concentrate adjutants increased frequency of arrested ear syndrome. This phenomenon is marked by normal plant development except for the ears.

“If you need to apply a fungicide before tassel, we recommended not including a nonionic surfactant or crop oil concentrate,” says Wise, Purdue Extension plant pathologist.

Adjuvants and herbicides know each other nearly as well as a couple at their 50th wedding anniversary party. Adjuvants and corn and soybean fungicides, though, mimic a newlywed couple — sometimes clicking along in unison and other times in confusion.