Philadelphia, Pennsylvania, USA
February 21, 2017
Overlapping residual herbicides used in conjunction with glyphosate and dicamba resulted in better weed control and higher yields than the post-emergent treatments used alone.
Monsanto’s Roundup Ready 2 Xtend® crop system and Dow’s Enlist Duo® herbicide-resistant seed traits are the next wave of trait technology designed to allow growers to spray herbicides without damaging the crop. The efficacy of these tools, however, could be short-lived if growers rely too heavily on them.
“There are a couple of things I have been telling growers with regard to this technology,” says Dr. Kevin Bradley, state extension weed scientist at the University of Missouri. “One is trait technology is a tool in the toolbox, not a silver bullet. Don’t buy into it thinking it is going to solve everything and all I have to do is spray this herbicide. That won’t work. Second, we have to use the same best management practices we are using now with these future production systems. Those include pre-emergence herbicides, which, in and of themselves, mean multiple modes of action and overlapping residuals as well.”
The companion herbicides to these two new trait technologies, Enlist Duo® herbicide with ColexD® technology, a premix of new 2,4-D choline and glyphosate, and Roundup Xtend™ herbicide, a premix of dicamba and glyphosate, use the same two sites of action, Group 4 (synthetic auxins) and 9 (EPSP synthase inhibitor), to manage weeds. Overreliance on the same sites of action can lead to resistant weeds.
Diversifying weed programs with residual herbicides that use different modes of action can preserve the effectiveness of the new seed traits as well as the new herbicide products designed to work with them.
University weed scientists recommend using a pre-emergent residual herbicide followed by a second residual herbicide prior to making the post-emergent application of Enlist Duo herbicide or Roundup Xtend herbicide to manage early weeds and introduce a different site of action. Overlapping residual herbicides reduce selection pressure in weed populations to slow the development of resistant weeds.
Bradley says keeping multiple effective sites of action in play is critical. He estimates that, without the use of pre-emergent residual herbicides or overlapping residual herbicides in combination with these new seed traits, resistance could develop in as few as three to four years.
“It will drive weeds like waterhemp to be resistant to a new mode of action where we didn’t have resistance before,” Bradley says. “That would be unfortunate because the ag industry does not have a plethora of new traits and herbicides coming on the market, so we need to preserve everything that we have.”
In 2016, FMC conducted field trials in Roundup Ready 2 Xtend soybeans to measure the performance of Authority® brand pre-emergent herbicides and Anthem MAXX® herbicide when used in conjunction with dicamba and glyphosate, the active ingredients in Roundup Xtend herbicide.
One trial conducted in Mt. Vernon, IL, showed Authority brand pre-emergent residual herbicides followed by Anthem MAXX residual herbicide in a Roundup Ready 2 Xtend cropping system resulted in better weed control than if Anthem MAXX herbicide, glyphosate and dicamba were applied alone. This overlapping residual herbicide program controlled 99 percent of the large crabgrass, morning glory spp. and waterhemp.
A second trial conducted by the University of Missouri compared the performance of pre-emergent Rowel™ herbicide and pre-emergent Authority brand herbicides in a Roundup Ready 2 Xtend cropping system. Results show that Authority brand herbicides controlled 91 to 99 percent of the weeds studied – cocklebur, pitted morning glory and yellow foxtail – compared to 64 to 94 percent of the weeds controlled by Rowel herbicide. Authority brand herbicides also showed a four to nine bu/A yield advantage compared to Rowel herbicide.
“These trials show that overlapping treatments such as Authority brand herbicides followed by Anthem MAXX herbicide plus glyphosate and dicamba consistently outperformed single pre treatments followed by glyphosate and dicamba at later efficacy ratings at sites with significant weed pressure,” says Nick Hustedde, FMC technical sales representative who conducted the Illinois trial.
Gail Stratman, midwest regional technical sales lead for FMC who conducted his own trials in Nebraska, says his data supports findings from the University of Nebraska. “Numerous trials have shown that pre-emergent treatments that reduce early weed competition enhance yields over post-only treatments in a dicamba-tolerant environment,” Stratman says. “This is as expected, but we have two new and favorable data sets now to confirm that."
*Anthem MAXX herbicide is not yet approved for tank mixing with glyphosate and dicamba.
1This was a research project. Ordinary glyphosate or dicamba formulations are not registered for commercial use on dicamba-tolerant soybeans.
About FMC
For more than a century, FMC Corporation has served the global agricultural, industrial and consumer markets with innovative solutions, applications and quality products. Revenue totaled approximately $3.3 billion in 2016. FMC employs approximately 6,000 people throughout the world and operates its businesses in three segments: FMC Agricultural Solutions, FMC Health and Nutrition and FMC Lithium. For more information, visit FMC.com.
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