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Adjuvants give fungicides a hand up

Agriculture.com Staff 04/26/2010 @ 8:08am

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.

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