All about adjuvants

Several years ago, Bryan Young needed some adjuvants for greenhouse herbicide tests. The Purdue University weed scientist visited a local retailer to buy these components, which maximize herbicide performance. 

“I asked if they had a certain adjuvant,” he says. “They told me, ‘Well, yes, but growers don’t use that one.’ ”

“But isn’t that your premium product?” Young asked. “They told me it was, but most growers told them it was too expensive. So they offered a cheaper one that wasn’t as effective.

“That really bothered me,” adds Young. “But I can see where they were coming from. In retail, you need to have a product that growers are willing to pay for. If your product is priced too high and the farmer would rather buy a cheaper one, then they will buy a cheaper one. If not, your competitor will have a cheaper one, and they’ll just buy that product.”

Long term, though, the only beneficiaries of this approach are weeds.  

“You get what you pay for in the adjuvant world,” says Ryan Wolf, WinField United agronomy services manager. “Just like anything, when you buy a cheap adjuvant, it likely has cheap inert ingredients and won’t perform like a top-tier adjuvant.”

Herbicide Fuel 

Numerous products fall under the adjuvant banner, but most can be grouped into surfactants, crop oil concentrates, and ammonia fertilizers that accompany herbicides into a spray tank. Adjuvants also include drift reduction agents (DRAs) that curb herbicide off-target movement and pH modifiers that reduce tank mix acidity. 

“I compare them to farmers adding fuel to a tractor to make it work,” says Wolf. “The adjuvant is basically the fuel for the herbicide to work. It’s the bridge to get that herbicide into, onto, and through
the plant.”

“If you don’t add them, reducing herbicide performance 30% to 90% is possible,” says Joe Gednalske, who heads membership and value promotion for the Council of Producers & Distributors of Agrotechnology (CPDA), an adjuvant trade group. Adding them can help erase this gap, but only if the correct one is used. This adds short-term expense, but also prevents long-term headaches like poor herbicide performance.

“If you select the wrong type of adjuvant that doesn’t match up with what each individual herbicide needs, there can be a 5% to 50% reduction in performance,”
says Gednalske. Meanwhile, picking a “good enough” adjuvant vs. a premium product can impact herbicide performance 5% to 25%, he adds.

“There’s also an increased risk of crop injury if farmers pick a crop oil when they were supposed to have a nonionic surfactant,” he says. 

Poor herbicide performance spurred by improper adjuvant selection also selects for resistant weeds. 

“Whenever you apply a herbicide, you try and optimize its activity,” says Young. “When the herbicide activity is compromised, we allow for low-level resistance [in a weed population] to survive.”

Don’t Skimp 

By themselves, adjuvants cost little. A nonionic surfactant, for example, that accompanies a herbicide may cost just 50¢ per acre, says Wolf. Still, the increasing complexity of today’s tank mixes adds adjuvant expense.

“Today, we’re mixing glufosinate [Group 10] with 2,4-D [Group 4],” he says. “If we have volunteer corn to control, that’s another chemistry [clethodim, Group 1] and an accompanying adjuvant,” says Wolf. 

Other mixes – such as dicamba and glyphosate – require a DRA and water conditioner that ease acid content of tank mixes by pushing pH above 5 (acid content increases as a solution moves downward on the 0 to 14 pH scale). “With dicamba products, adjuvant costs can be closer to $5 to $7 per acre,” Wolf says. 

Still, picking the higher-priced optimal adjuvant pays long term, he advises. 

“When you spray weeds – especially with the weather patterns we’ve been having the last two to three years – you only have one chance to do it right,” he adds. “If you don’t do that, it will cost you a lot more money. That’s not only true with resprays, but in yield potential, too.”

Buyer Beware

Young last compiled a compendium in 2016 that lists 670 adjuvants from 38 manufacturers. It’s likely, though, that manufacturers annually sell over 2,000 adjuvants, with many having two or more functionalities across 14 categories, says Gednalske.

“This increases the degree of difficulty in finding the right adjuvant system,” Gednalske says. 

A buyer beware mentality also rules the adjuvant world. 

“Except for in states like California, Washington, and a few others, there is no regulation of adjuvants,” says Gednalske. “If anyone wants to make an adjuvant in their bathtub with materials around the house, they can do so and legally sell them in nearly every state in the U.S. Water is a cheap active ingredient, and a lot of the lower priced ones have lots of water.”

Misleading adjuvant claims also abound. “An adjuvant is not going to help glyphosate control a glyphosate-resistant weed,” says Wolf. “There are a lot of ‘watch-outs’ in claims like these.” 

It’s here where a reputable dealer can help farmers pick the adjuvants to optimize herbicide performance, adds Wolf. “Ask for efficacy data, such as from a third party or a reputable source,” he says.

Adjuvants that meet CPDA certification are also a wise choice. Products enrolled in CPDA’s certification program must meet 17 benchmarks defined by the ASTM International, a group that establishes testing standards and methods for industries worldwide. Approved adjuvants must go through a rigorous science-based testing process and state active ingredients and other materials, says Gednalske. 

Thus far, 15 manufacturers market CPDA-certified adjuvants. Currently, 480 herbicide labels state that a CPDA-certified adjuvant must be used, says Gednalske. 

“A company that certifies their products demonstrates they will back their product and be in the marketplace for a long time,” says Young. “That is why we recommend CPDA-certified adjuvant products.”

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