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Corn+Soybean Digest

Glyphosate Is Glyphosate OR IS IT?

The acreage of Roundup Ready soybeans has, of course, mushroomed … and so have the number of glyphosate herbicide products to treat those beans. The question is: Does one product perform better than the rest, or do they all work about the same?

Although some manufacturers claim superiority for their products, university testing and farmer experience say there's not much difference in performance among the pack. That's assuming they're used at recommended rates and according to directions.

“Regardless of the brand you purchase, the active ingredient for all glyphosate products is exactly the same,” points out Iowa State University (ISU) weed scientist Bob Hartzler.

ISU conducted 11 field trials, comparing the performances of Roundup UltraMax, Touchdown IQ, Glyphos Gold, Glyphomax Plus or other brands of glyphosate.

“In 91% of the comparisons, there were no differences in performance when comparing products at equivalent rates of active ingredient with recommended additives,” Hartzler reports. “These data suggest performance differences among glyphosate brands are small and should not be a major criteria in product selection.”

In Michigan State University (MSU) comparisons of Roundup UltraMax, Touchdown IQ and Glyphomax Plus, there were no differences in weed control when all were applied at full rates. However, with low application rates and large weeds, differences in formulations or additives were more easily detected.

“When glyphosate is applied to small, actively growing weeds at recommended rates, all glyphosate formulations should be effective,” says MSU weed scientist Jim Kells.

Bryan Young, weed scientist at Southern Illinois University, has compared Roundup Ultra, Roundup UltraMax, Roundup WeatherMax, Glyphomax Plus, Touchdown IQ and Clearout 41 Plus at full recommended rates and also at one-quarter rates. He has tested with and without ammonium sulfate. Except for Roundup WeatherMax, which was not available until 2002, he's done multi-year comparisons.

“In all our years of testing, I've seen very few, if any, differences in performance among the products when used at full rates,” Young says. “At the one-quarter rate we've seen some differences in control of some weed species in some years, but no best product for all situations. As you reduce rates, you increase variability.”

University of Illinois weed scientist Aaron Hager says, “We, and other universities, looked at several glyphosate formulations in the field last summer, but overall differences were minor.”

What about on-farm experiences? Grower John.

Gruber is also an independent crop consultant and contract researcher in New Holland, OH. He has observed the performances of Roundup Original, Roundup UltraMax, Touchdown IQ and Glyphomax Plus on his and clients' farms.

“I've seen little difference among the four products if timing is right,” Gruber says. “Therefore, I recommend the most economical product. In addition to price, we look at the support behind the product regarding respraying and replanting. I truly believe glyphosate is glyphosate.”

The Triumph Co-op, Triumph, IL, has sold and applied Roundup UltraMax, Touchdown IQ and other glyphosates. “We haven't seen any noticeable difference in performance among them,” reports Cal Sellers, agronomist.

Sellers says that proper application timing is the key, regardless of the product. “Weeds need to be sprayed before they get too big or none of the glyphosates will perform at maximum,” he notes.

Time of day also is important. “None of the glyphosate products is as effective if we apply before 7 or 8 a.m. and after 6 p.m.,” he notes.

Sellers points out that glyphosate products marketed by the major chemical companies have the best respray and replant guarantees.

Farmer-inventor Marion Calmer, Alpha, IL, says he found no difference in yield between Roundup Ready soybeans treated with Roundup UltraMax and those treated with Touchdown IQ.

At Janesville, WI, Tim Maloney, a farmer, private researcher and crop consultant, did find some slight differences in his 2002 glyphosate testing. He compared Roundup UltraMax, Touchdown IQ, Glyphomax Plus and Glyphos Gold. Plant stands were uniform in all treatments.

“Weed control was similar among all treatments, with about 95% overall performance,” Maloney reports. “However, there was some later waterhemp in the Glyphomax Plus plots.”

Maloney says there was some early yellowing of leaf veins that was more pronounced in the plots treated with Glyphomax Plus and Glyphos Gold, compared to Roundup UltraMax and Touchdown IQ treatments. The yellowing was in the first two to three trifoliates and tended to disappear within about 14 days after herbicide application.

“Surprisingly,” says Maloney, “there were some differences in yield. Touchdown IQ plots yielded 52.4 bu/acre, Roundup UltraMax plots went 52.2 bu/acre, Glyphomax Plus plots were 48.2 bu/acre and the Glyphos Gold plots ran 46.7 bu/acre. Statistically, that put the Touchdown IQ and Roundup UltraMax yields in one category and the Glyphomax Plus and Glyphos Gold plots in another lower category.”

Chemical Companies Comment

We asked two glyphosate manufacturers, Syngenta (Touchdown IQ) and Monsanto (Roundup brands), whether there was a difference in performance among glyphosate products.

“We believe the big advantage for Touchdown IQ is consistency of performance,” says Bill Beutke, Touchdown product manager. “This means more consistent performance over a wider set of environmental conditions and greater number of weed species.”

Beutke says Touchdown IQ requires a minimum of adjuvants and 25% less ammonium sulfate, compared to competitor products. “We also offer a better replant and performance guarantee in our Touchdown Assurance Plan,” he says. “It covers all brands of Roundup Ready seed.”

Monsanto says its Roundup WeatherMax delivers more glyphosate to the roots and provides more consistent control than Touchdown IQ. “That consistency is present even under tough spray conditions,” says David Heering, Roundup technical manager for Monsanto.

Heering says eight of 10 growers spray under challenging conditions and that's the reason Monsanto evaluates products under tough conditions. “As a result, Monsanto has developed its Roundup WeatherMax, which offers the industry's first 30-minute rain-fast warranty.”

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