Sept. 23, 2005

COLUMBIA, MO - Monsanto and the University of Missouri are investigating a potential case of glyphosate-resistant waterhemp on two fields in northwest Missouri. In initial greenhouse trials, the waterhemp plants were not controlled at labeled rates. Field and heritability studies are needed to determine if these populations are resistant to glyphosate.

"We're looking at waterhemp populations on two fields where there has been a history of performance issues," says Dr. Kevin Bradley, University of Missouri Extension Weed Scientist. The fields in question are owned by two growers, both of which have grown continuous Roundup Ready soybeans for the past few years.

"Our greenhouse trials show differing levels of response, including some plants that survive following application with above labeled rates of glyphosate," says Bradley. "However, field studies have not been conducted to confirm resistance in these populations. Field studies are scheduled for 2006 to gain a better understanding of what we have."

Waterhemp is an annual weed prominent across the corn and soybean belt. It produces an abundant number of small seeds, grows quickly and germinates over time, which means producers must contend with multiple flushes during the growing season. Postemergence herbicides are most effective when applied before the weed reaches six inches in height.

"Monsanto takes product stewardship very seriously, and we are working with the University of Missouri to follow up with these growers and provide effective recommendations," says Jennifer Ralston, Roundup Technical Manager for Monsanto. "In Roundup Ready soybeans, we recommend that growers who have dense stands of weeds, such as waterhemp, use a preemergence residual product such as INTRROTM or Valor®. Additionally, in this situation the growers should consider the agronomic benefits of rotating to Roundup Ready corn." Some benefits of a corn-soybean rotation include the ability to use different herbicides, alternative cultural practices and the disruption of disease and insect pressure.

Monsanto recommends the following set of weed management practices to help growers minimize the risk of developing resistant weeds:

• Start with a clean field by either utilizing a burndown herbicide or tillage and control weeds early.
• Use Roundup Ready technology as the foundation of your weed management program.
• Add other herbicides or cultural practices where appropriate as part of the Roundup Ready cropping system.
• Use the right herbicide rate at the right time.
• Control weeds throughout the season and reduce the weed seed bank.
• Monsanto continually evaluates its recommendations for effective weed control and will provide alternate weed control recommendations if this biotype is confirmed as resistant. When glyphosate resistant weed biotypes have been identified, they have been effectively managed with other herbicides and/or cultural practices.

Monsanto Company is a leading global provider of technology-based solutions and agricultural products that improve farm productivity and food quality. For more information on Monsanto, see: www.monsanto.com