In recent weeks, Monsanto has been alerting seed dealers and chemical suppliers to the potential for injury from some glyphosate herbicides…

Farmers who opt to apply a glyphosate-based herbicide other than Roundup Ultra or Roundup UltraMax over the top of their Roundup Ready cotton run the risk of injuring their crop or reducing yields, Monsanto says.

While that might sound like a ploy to sell more Roundup Ultra or UltraMAX, Monsanto representatives say their studies show that using other glyphosate herbicide formulations — including their own — can produce less than desirable results in Roundup Ready cotton.

“We were interested in labeling other Monsanto glyphosate formulations for use in Roundup Ready cotton,” said David Heering, technical manager for Roundup herbicides at Monsanto. “But, all of our tolerance and gene equivalency data was based on applications of Roundup Ultra and UltraMAX. So, we made a commitment to look at other formulations in combination with surfactants to evaluate crop safety.

“The results of our research demonstrated that addition of surfactant to various formulations of glyphosate could result in significant vegetative injury compared to Roundup Ultra or Roundup UltraMAX applied alone. Based on these results, Monsanto is not willing to label and promote Roundup Original or other glyphosate formulations that require the use of surfactant for use in Roundup Ready cotton.

Heering said the Monsanto representatives, who conducted the study at numerous locations across the Cotton Belt in 2000, observed visual injury as high as 59 percent leaf speckling when additional surfactant was added to Roundup Ultra, Roundup UltraMAX and other glyphosate formulations.

In another portion of the study, the scientists saw a shift in fruit retention and a yield reduction with the addition of a non-ionic surfactant compared to plots that were sprayed with Roundup Ultra or UltraMAX alone.

“We did not see a yield reduction in every location or with every glyphosate formulation or surfactant,” said Heering. “When testing a formulation by surfactant and by environmental interaction, it becomes difficult to predict when the problems will occur.

“Based on those findings, we decided we could not label and promote products that might be used with surfactants for application over-the-top of Roundup Ready cotton,” he said.

What's the difference in using Roundup Ultra or Roundup UltraMAX, Heering was asked.

The experience and expertise Monsanto has with Roundup herbicides and the performance of our Transorb technology (the technology which helps translocate the herbicide through the plant and into its roots),” he said. “The Transorb technology is the same today as it was last year or the year before. If you choose five commercial surfactants, each is designed to do something different. So, they may not be as consistent in their performance as the Transorb technology.”

Monsanto scientists are repeating the study in 2001, but Herring is doubtful the company will change its position. “The results from the 2000 season were so overwhelming, that we would be reluctant to go ahead with new recommendations. Even if it didn't happen in 2001, the odds become 50-50 it could happen again. We will continue our testing and communicate the results when available.”

In recent weeks, Monsanto has been alerting seed dealers and chemical suppliers to the potential for injury from some glyphosate herbicides that require the addition of a surfactant to enhance performance.

Delta and Pine Land Co., one of Monsanto's seed company partners, has also been notifying distributors that its Roundup Ready-tolerant varieties have only been tested with Roundup Ultra and Roundup UltraMax herbicides.

“Basically, we're saying that we have tested our varieties for tolerance and it has been with the two Monsanto-recommended formulations,” said Tom Kerby, vice president for technical service with the Scott, Miss.-based company.

Kerby noted while many products are available for use with a range of surfactants, this greatly expands the number of outcomes that can occur in the plant's response to the glyphosate application.

“We feel we must maintain a standard reference to measure the tolerance of our varieties. A testing program to establish the tolerance of multiple formulations of glyphosate with multiple surfactants would require tremendous resources and be beyond the scope of a seed company's variety development program,” he said.

“We think it's up to the manufacturers of those products to test them and report their results.”