University of Missouri research shows generic glyphosates work. And they may be cheaper. Yet price isn't the only factor to consider when selecting a glyphosate herbicide.

Since Monsanto's patent expired on glyphosate (the active ingredient in Roundup), other companies have rushed to manufacture the popular weedkiller. Now, more than two dozen firms in the United States and foreign countries are producing their own versions of glyphosate.

The generics typically are cheaper--by as much as $2 per gallon. But, are these Roundup generics as effective as the real thing? To help answer that question, Andy Kendig, weed specialist at the University of Missouri's Delta Center in southeast Missouri, compared several different versions of glyphosate on Roundup Ready soybeans. The Missouri Soybean Merchandising Council helped fund the research. The compounds compared, along with the results, are shown in the included table.

"We saw only minor differences among the glyphosate formulations, and those differences most likely were due to variations in weed populations from plot to plot," said Kendig. "However, there are some differences in these products; different surfactants or no surfactants blended in. To keep the comparison even, we used the recommended surfactant with each product."

All herbicides were applied at a rate to make them equal to 1 quart per acre of Roundup original. Sprays were made when weeds were about 2 inches tall.

In bids to capture a share of the huge glyphosate market, companies have come out with aggressive advertising. Some produce computer-generated color photos supposedly showing that a particular product translocates better than another.

"However, no company apparently can show that their product actually controls weeds better," said Kendig, who then added jokingly: "If a sales rep can prove that his glyphosate provides greater than 100 percent weed control, you should use his product. But if that type of data existed, the advertisements would show weed control, instead of computer-generated photos. In our study, there was no measurable difference in the efficacy of different versions of glyphosate."

While Kendig saw little difference in different forms of glyphosate, the level of customer service may be something else.

"Obviously, Monsanto is not going to stand behind another company's generic product," he said. "Most major chemical companies have representatives to help you if something goes wrong. Smaller manufacturers may not provide as good support. It may be worthwhile to choose the product of a trusted company than to take a chance on a new, unsupported brand of glyphosate."

Marvin Rohrbach, manager of MFA's crop protection division, agrees. Rohrbach categorizes glyphosate products into three levels:

1. True generics, produced by minor companies or off-shore manufacturers;
2. Generics produced by major chemical companies;
3. Roundup brand glyphosate produced and marketed by Monsanto.

"The value of having a company stand behind its product is especially important if you have to replant," Rohrbach said. "Last year, we had support for replant and respray.With the season we had, we answered some calls. Some of the so-called generics are produced by companies that give good support; others--especially some glyphosates produced overseas--may be less reliable."

When conditions cause a replant, using branded Roundup on Roundup Ready soybeans may be more palatable financially. Monsanto used to charge a "tech fee" for the Roundup-resistant trait. Now a royalty or licensing fee is charged by Monsanto to the seed company, which passes the cost (usually $6 to $6.50 per bag) on to the grower in the price of the seed.

"When a grower is forced to re-plant, Monsanto usually will forgo the fee on the new seed needed, if the grower is using Roundup," said Rohrbach. "Monsanto is not as likely to refund the fee for growers who are not using Roundup."

"If commodity prices were a bit better, I think most growers would stay with Roundup," said Andy Kendig. "Most companies give lip service to standing behind their product, but some are better than others at living up to it."

Still, on the basis of how well it works, there is little difference among glyphosates now being produced.

"The surfactant package may vary among the different glyphosate products being sold. That could affect how well the chemical works," said Rohrbach. "But all glyphosate seems to work. Just be sure to keep rates up, and use over-the-top glyphosate before weeds get too tall."

See also: Weed control comparison of different products