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CropTalk: A New Spin on Pre-Emerge Herbicides

June 2020

Published on Monday, June 01, 2020

In the weed science world, we spend a lot of time discussing soybean herbicide programs, but very little time talking about corn programs. Why is so little time spent on corn? One reason is the fact that we can use Group 27 or HPPD herbicides in corn to achieve effective weed control. HPPDs were approved in the late ‘90s, making them the most recently approved herbicide group to come to market. Therefore, there are fewer resistant weeds reported compared to many other herbicide groups. Today, Group 27 herbicides are the foundation to many successful corn herbicide program. However, in 2020, farmers in approved states/counties will have the option to use Alite™ 27 (isoxafl utole) for residual on tough-tocontrol small-seeded broadleaf weeds, such as pigweeds and marestail. Alite 27 has greater activity on smaller-seeded broadleaf weeds versus larger-seeded weeds like giant ragweed.

What are the strengths of Alite 27? It is a pre-plant/pre-emerge Group 27 herbicide for LibertyLink® GT27™ (Beck's Freedom Plus® series) soybeans. One advantage of Group 27 herbicides is their “reach back” capability. Residual herbicides require rainfall to be activated; the herbicide needs to be in solution so that germinating weeds can take it up. The amount of rain required for activation depends on the solubility of the herbicide. If weeds germinate before activation, Group 27 herbicides like Alite 27 can “reach back” and control small weeds that have already germinated.

What are pre-emerge tank mix options? Beck’s Practical Farm Research (PFR)® data has demonstrated that using three sites of action (SOAs) will result in the greatest waterhemp control compared to one or two SOAs. Not only will increasing the number of SOAs provide greater control, but it will also result in broader spectrum weed control. Adding products such as Zidua® SC will increase Alite 27’s grass control and provides two effective SOAs on pigweeds. According to the Alite 27 label, other residual tank mix options include metribuzin and PPO herbicides like fl umioxazin and sulfentrazone. Metribuzin, fl umioxazin, and sulfentrazone increase waterhemp control but would have limited grass control.

What about emerged weeds? Alite 27 will have activity on many of the challenging weeds you may face when weeds are 1 to 3 in. tall. However, the higher rate will result in greater efficacy versus the lower rates on many large-seeded broadleaf weeds like giant ragweed and cocklebur, along with tough to control small-seeded broadleaf weeds such as waterhemp. However, depending on soil type and application timing, the higher rate may not be allowed on your soil. Therefore, tank mixing another SOA herbicide with burndown activity is critical if weeds have already emerged. Products such as Gramoxone®, 2,4-D (which bears a plant-back restriction) and glyphosate can be tank mixed to enhance burndown activity. Liberty® can also be tank mixed but should be avoided if used in the post-emergence trip to prevent an overreliance on one SOA.

What about residual herbicides with burndown activity? One pre-emerge herbicide option is Zidua® Pro. Zidua Pro contains Sharpen®, which has burndown activity. Beck’s two-year PFR data on Zidua Pro shows 96% waterhemp control 45 DAT. Pairing Zidua Pro (Figure 1) with Alite 27 provides three effective SOAs on ALS resistant waterhemp.

What about the post-emergence trip? Beck's Freedom Plus series soybeans are tolerant to Liberty and glyphosate. Our PFR data shows that waterhemp control with Liberty + glyphosate increases by 12% compared to Liberty alone, and 53% compared to glyphosate alone. Just like any program, adding an in-season residual like a Group 15 will help reduce the number of late-season escapes. Beck’s PFR data has shown a 6% increase in control across multiple trait platforms when a Group 15 is used in-season. Alite 27 will bring another effective SOA to farmers planting Beck's Freedom Plus soybeans.

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Joe Bolte
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