James Ritchie

Crop growers need to know how to use a host of crop-protection products, from Accent to Zorial. And a dozen or more new compounds and premixes hit the market each year.

But your chemistry homework doesn't end there. You also need to know which adjuvants to add to the tank to make the spray stickier, slicker or more effective.

"Adjuvants generally are designed to be 'activators,' to make a herbicide work better or more effectively," says Marvin Rohrbach, crop protection manager for MFA, Inc. "Most surfactants, for example, are needed for consistent performance of the weed-control product."

When you're looking for information on which additive to use, the herbicide label is the best place to start. You probably should recheck the label for new formulations or tankmixes.

For example, Roundup Ultra has an adjuvant blended in; original Roundup does not - you'll need to use a surfactant. And both formulations work better if you add 17 lbs of ammonium sulfate per 100 gallons of spray mix.

The shift from tillage to no-till has seen the development of new, highly specialized spray adjuvants, like drift-control agents.

"With a few exceptions, most over-the-top herbicides will need something else added to the tank, either by the manufacturer or by the applicator, as a tankmix in the spray solution," says Bryan Young, weed control specialist at Southern Illinois University.

"With some herbicide-weed combinations, the product's performance depends on the proper adjuvant."

In many cases, this makes the adjuvant about as important as the herbicide. Unfortunately, spray adjuvants aren't subject to the same labeling requirements, and there's a brisk market in them.

"There's a very open and competitive market in these products, and you cannot tell what's in the container when you buy an adjuvant. There's a wide range in price and quality, too," Young continues.

"It's a good idea to buy from reputable manufacturers and dealers who stand behind their products," he says.

"If your dealer plans to be in business for very long, he isn't likely to sell you inferior-quality products. You can probably find cheaper adjuvants from some salesmen, but this may not be the place to cut costs. The most expensive weed control program is the one that doesn't work."

Last year, Young succeeded George Kapusta, the long-time weed control specialist at Southern Illinois University.

"I will be doing research on spray adjuvants, and I'll continue publishing the compendium," he says.

Young is referring to the Compendium of Herbicide Adjuvants, which has been published by Kapusta since 1992. For a copy, send $3 to Bryan Young, Department of Plant, Soil and General Agriculture, Southern Illinois University, Carbondale, IL 62901 -4415.