Ask About Adjuvants

March 26, 2011 12:43 AM

An adjuvant paired with the right herbicide can put money in your pocket. The opposite is just as true. The challenge is in recognizing the difference between the two—which is not always an easy task.

No regulatory agency oversees the licensing or marketing of adjuvants, so product claims don’t necessarily match product performance, notes Richard Zollinger, Extension weed scientist, North Dakota State University.

However, Zollinger says, the correct adjuvant, when added to the spray tank, will improve handling and/or weed control results. In some cases, adjuvants can even help reduce the amount of herbicide needed in the tank for good weed control.

The right adjuvant is key, says Bryan Young, weed scientist, Southern Illinois University. "We have to be sure that we optimize the adjuvant system for any foliar herbicide application to have a chance at controlling these problematic weeds," he says.

Common adjuvants include surfactants, crop oil concentrates, nitrogen sources, water conditioners, compatibility agents and drift control agents.

Historically, adjuvants have fit into three basic categories: activators, spray modifiers and utility modifiers. The terms "adjuvant" and "surfactant" are not always interchangeable.

"A surfactant is a type of adjuvant ingredient that modifies the surface properties of the spray solution, typically reducing surface tension and allowing for greater interaction or spread of spray deposit on target leaf surfaces," Young says.

There’s a new category of adjuvant, Young says, called high-surfactant-oil concentrates (HSOC). These products are made up of a minimum of 50% oil and between 25% and 50% surfactant. HSOC products are often used in spray-mix combinations of glyphosate and ACCase (post graminicide) herbicides to control volunteer glyphosate-resistant corn, among other uses.

Pricewise, adjuvants cost between 25¢ per acre to more than $3 per acre. As often is the case, the more you pay, the better your chances are of using a product that provides a benefit, though cost is not a sure indicator.

Reading the product label is still the best way to determine whether a product will work more effectively when paired with an adjuvant.

"Select adjuvant products from manufacturers that provide research data with their products over multiple experiments and years," Young says.

According to Mark Bernards, University of Nebraska–Lincoln Extension weed scientist, the Chemical Producers and Distributors Association began a certification program in 2001 to increase the consistency of adjuvant product performance. The program is voluntary. Bernards says products must meet 17 standards developed by ASTM International in order to be certified.

To help separate the facts from fiction for 622 adjuvants from 36 companies, Young compiled a pocket-sized booklet, Compendium of Herbicide Adjuvants. Contact Young at (618) 453-7679 or to buy a copy for $3.


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