Use Diversified Programs to Preserve Efficacy of Weed Control Tools
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Sustainable weed control costs money. Failure to control weeds this year can end up costing a lot more in the long run. According to a recent Purdue University study, using a diversified herbicide program approach and incorporating Enlist® herbicides into your herbicide program may be the most effective way to reduce weed density, the number of weed species in a field and weed seedbank.1
The seven-year Purdue study shows relying heavily on 2,4-D in a nondiversified approach increases both the weed seedbank and number of species in a field over the years. However, a fully diversified 2,4-D strategy employing seven modes of action will reduce the total weed density and, therefore, mitigate the evolution of herbicide resistance.
Hodgskiss, C. L., T. R. Legleiter, B. G. Young, W. G. Johnson. 2022. Effects of herbicide management practices on the weed density and richness in 2,4-D-resistant cropping system in Indiana. Weed Technol. 36: 130–136.
Key:
Diversified Glyphosate:
• Corn: 3 MOA PRE & 3 MOA POST
• Soybeans: 3 MOA PRE & 2 MOA POST
Diversified 2,4-D:
• Corn: 3 MOA PRE & 2,4-D and Glyphosate POST
• Soybeans: 3 MOA PRE & 2,4-D and Glyphosate
2,4-D Reliant:
• Corn: Atrazine PRE & 2,4-D + glyphosate POST
• Soybeans: 2,4-D & glyphosate POST only twice in season
Fully Diversified:
• Corn: 3 MOA PRE & 3 MOA POST
• Soybeans: 3 MOA PRE & 2,4-D MOA POST
“This is why Corteva has always and will continue to promote the use of fully diversified weed control programs that includes tank-mixing multiple modes of action in the Enlist weed control system,” says Steve Snyder, Enlist field specialist for Corteva Agriscience. “When using Enlist herbicides in a program approach that features multiple modes of action and overlaying residual herbicides, growers will be able to mitigate the evolution of resistant weeds in a rotation of Enlist corn and Enlist E3 soybeans.”
Snyder promotes a zero-tolerance policy for weeds. This requires the use of multiple herbicide modes of action through preemergence, postemergence and residual herbicide applications and removing any escapes before weed seed replenishes the soil seedbank.
“Because of increased input costs and lack of supply of needed products, too many shortcuts are being taken in many current weed control programs,” Snyder says. “Mitigating the evolution of resistance in weed species requires a long-term approach. It requires foresight to consider the potential impacts to farm profitability that resistance weeds can cause.”
Snyder says those impacts to profitability can include trait costs, herbicide expenses, hand-weeding costs and labor and equipment expenses. To avoid decreases in farm profitability down the road, he recommends using the best resistant management tool we have: managing the soil seedbank.
“Don’t allow escapes in your weed control program. It sounds simple but takes a motivated individual to follow through. Adopting a zero-tolerance policy for weeds and reducing that seedbank for a three- to five-year period helps arrest the emergence of weeds like Palmer amaranth or waterhemp,” Snyder says. “If these and other weed populations are reduced in a field by adopting a zero-tolerance policy, there is significantly less selection pressure on the valuable herbicides we use. This reduction in selection pressure will lengthen the useful life of these valuable tools.”
Arkansas: a case study for resistant weeds
Tom Barber, Ph.D., a University of Arkansas professor and Extension weed scientist, also advocates for a zero-tolerance policy on weeds.2 He notes that some Arkansas growers have lost the ability to control weeds with glyphosate and other chemistries and that other herbicides may soon face the same fate unless growers realize the need to consistently use multiple modes of action. The lack of effective herbicide options leads to significantly higher weed control costs in future years.
Barber contends growers need to adopt weed management plans to preserve the efficacy of herbicides, keeping them viable and keeping weed management costs under control. He adds that managing the weed seedbank is critical. “The seedbank must be stable or decreasing to be sustainable,” he says.
For example, a single Palmer amaranth plant can produce anywhere from 300,000 to 1 million seeds per plant. That means that 95% weed control won’t help reduce Palmer amaranth pressure.
Barber suggests a combination of crop rotation, deep tillage and manual weed control (hoeing) may be necessary to manage the weed seed bank and control weeds long term.
“We need to steward the herbicides that are still effective,” Snyder says. “Some areas are down to their last tool for postemergence control of Palmer amaranth. If these herbicides stop working, the cost of weed control will be prohibitive.”
Snyder says herbicide costs in Arkansas can be more expensive by $40 to $100 per acre after Palmer amaranth, which is resistant to multiple modes of action (ALS, PPO, glyphosate, S-metolachlor), takes over a field.
Fortunately, there are tools out there to help. A tank mix of Enlist One® and Liberty® herbicides offers the most effective postemergence control of pigweed species resistant to glyphosate, PPO, ALS and S-metolachlor. The Enlist® weed control system is the only system that allows for the tank mix of an auxin herbicide and glufosinate.
Going into next season, make sure you are planting a soybean or cotton variety that allows you to use a mixture of two effective modes of action to control troublesome weeds. Adopting a diversified herbicide program is essential to ensuring stable farm profitability for years to come. Using combinations of these tools can deplete the seedbank and ward off the development of resistant weeds. If you don’t limit the weed seedbank, those seeds may empty your bank account.
1Hodgskiss, C. L., T. R. Legleiter, B. G. Young, W. G. Johnson. 2022. Effects of herbicide management practices on the weed density and richness in 2,4-D-resistant cropping system in Indiana. Weed Technol. 36: 130–136.
2Barber, T. 2016. Zero Tolerance: Designed for Seedbank Reduction. https://www.planthealthexchange.org/cotton/Pages/GROW-COT-10-16-083.aspx
™ ® Enlist, Enlist Duo, Enlist E3, the Enlist Logo and Enlist One are trademarks of Corteva Agriscience and its affiliated companies. ® Liberty is a registered trademark of BASF. The transgenic soybean event in Enlist E3® soybeans is jointly developed and owned by Corteva Agriscience and M.S. Technologies, L.L.C. Enlist Duo® and Enlist One® herbicides are not registered for sale or use in all states or counties. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Enlist Duo and Enlist One herbicides are the only 2,4-D products authorized for use with Enlist® crops. Consult Enlist herbicide labels for weed species controlled. Always read and follow label directions.