When it comes to weed control for corn and soybeans, we talk quite a lot about controlling broadleaves. While it’s extremely important to do so, sometimes we don’t focus quite as strongly on grass weeds. However, those grasses also can cause yield loss, and some of them are quite tricky to control.
Iowa-based Pioneer agronomist Nate LeVan has advice to help you keep grass weeds at bay in your corn and soybean fields.
When it comes to controlling grasses like foxtail and woolly cupgrass, for example, LeVan says it’s very important to stay ahead of the weed populations. “Early season suppression of grass weeds is critical for maximizing yield, especially in a corn crop," he says.
LeVan recommends beginning each season with a clean, weed-free seedbed to maximize yield. A critical followup component to that is a two-pass herbicide program approach.
“Early season suppression of grass weeds is critical for maximizing yield, especially in a corn crop.”
“Using a two-pass approach is best when it comes to grasses like foxtails and especially woolly cupgrass in corn. With nonherbicide-tolerant/conventional hybrids, I recommend a full rate of a Group 15-containing residual solution like Surpass NXT herbicide, Resicore herbicide, Cinch ATZ herbicide, FulTime NXT herbicide or Keystone LA NXT herbicide preemergence in combination with a product like Accent Q herbicide in your postemergence pass to give those grasses different modes of action,” LeVan explains. “In herbicide-tolerant hybrids like the Optimum AcreMax family or Pioneer brand Qrome products, you have some postemergence options like glyphosate or glufosinate that do a really nice job cleaning up any grass escapes with the postemergence pass, as they can be very effective grass killers.”
When it comes to controlling grass weeds in soybean fields, LeVan says, the approach is similar.
“I recommend the same two-pass regimen, starting with a preemergence solution like Sonic herbicide. And there are a few more herbicide groups beyond Group 15 like Group 3 that work well as preemergence products that do a nice job on grasses in conventional soybeans,” LeVan explains. “Glyphosate and glufosinate herbicides in herbicide-traited soybeans like Enlist E3 soybeans also are very effective at managing grass weeds.”
And for postemergence residual control of grasses, LeVan says, DuPont™ EverpreX® herbicide is a good option for all soybean types. He recommends Enlist One® herbicide with glyphosate or Enlist Duo® herbicide for a postemergence application to control grasses and broadleaves in Enlist E3® soybeans.
LeVan says there are a few natural attributes that make some weeds easier to control than broadleaves. “Grasses like foxtails also tend to emerge over a shorter window of time, and the shading effect of the crop does a nice job suppressing grass weeds if you have a nice dense stand of corn or soybeans,” he says.
However, that is not the case with every species. “Woolly cupgrass is an exception to the rules above when it comes to emergence and is a bit more problematic. It will emerge over a long period of time, has larger seed reserves and will emerge from greater soil depths," LeVan says.
“Woolly cupgrass is an exception to the rules above when it comes to emergence and is a bit more problematic. It will emerge over a long period of time, has larger seed reserves and will emerge from greater soil depths.”
He also says woolly cupgrass caught a lot of Iowa farmers by surprise during the 2020 and 2021 growing seasons. The weed emerged after herbicide residual activity stopped, causing yield loss in some cases. He says that’s just one reason why a two-pass herbicide program is so important — and so is the timing of those passes.
“Two-pass herbicide programs are often more effective at controlling that weed versus preemergence-only programs with Group 15 herbicides. Because of herbicide-resistant weeds like giant ragweed and waterhemp, I believe we have focused on broadleaves and timing our postemergence pass so much to combat broadleaves in corn, that I think we have lost a little bit of our late-season control of woolly cupgrass,” LeVan explains. “The preemergence herbicides only work for about 20 to 35 days. And if a postemergence pass of a herbicide such as glyphosate or glufosinate is put on too early to kill broadleaves, like giant ragweed or lambsquarters, you can miss that late flush of woolly cupgrass.”
LeVan says you’ll want to consider all the weeds you need to deal with in your fields and create a holistic approach to controlling them for the best yield potential. He advises sitting down with your trusted advisers and planning out the best solutions and the best timing to ensure your fields are safe from both broadleaves AND grasses. Don’t let any of these weeds catch you by surprise in 2022.
Cinch® ATZ, FulTime® NXT and Keystone® LA NXT are Restricted Use Pesticides. The transgenic soybean event in Enlist E3® soybeans is jointly developed and owned by Corteva Agriscience LLC and MS 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. DuPont™ Accent® Q, Cinch ATZ, EverpreX®, FulTime NXT, Keystone LA NXT, Sonic and Surpass® NXT are not registered for sale or use in all states. FulTime NXT, Keystone LA NXT and Surpass NXT are not available for sale, distribution or use in Nassau and Suffolk counties in the state of New York. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Consult the label before purchase or use for full details. Agrisure® is a registered trademark of, and used under license from, a Syngenta Group Company. Agrisure® technology incorporated into these seeds is commercialized under a license from Syngenta Crop Protection AG. Roundup Ready® is a registered trademark used under license from Monsanto Company. Liberty®, LibertyLink® and the Water Droplet Design are trademarks of BASF. Qrome® products are approved for cultivation in the U.S. and Canada. They have also received approval in a number of importing countries, most recently China. For additional information about the status of regulatory authorizations, visit http://www.biotradestatus.com/. Always read and follow label directions.
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