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CropTalk: Is Weed Control Simple Again?

December 2019

Published on Wednesday, December 4, 2019

Has weed control in soybeans become simple again? In the 2020 growing season, farmers will have more effective soybean post-emergence platforms to select from than ever before. Are the days of having problematic weeds such as waterhemp, marestail, and giant ragweed sticking above the canopy over?

Though every one of these platforms will result in effective weed control, each system’s keys to success may vary. With every trait platform, the importance of residuals to reduce selection pressure on the post-emergence herbicides cannot be overstated. Using pre-emerge herbicides with multiple sites of action (SOAs) not only reduces the number of weeds, but also broadens the weed control spectrum. Beck’s Practical Farm Research (PFR)® data has shown waterhemp control 45 days after treatment (DAT) is 29% higher when using two SOAs and 37% higher with three SOAs compared to one SOA. Typically, pre-emerge herbicides will result in effective control for three to five weeks, depending on rainfall.

However, we may not have full canopy closure when the post-emergence herbicide application is made. Therefore, applying a Group 15 as an in-season residual could provide up to another four weeks of residual activity, providing time for full canopy closure. PFR data from three years of studies show a 6% increase in waterhemp control at the end of the season when using an in-season residual. Though 6% may not sound substantial, when a single waterhemp plant can produce 800,000 seeds, the reduction of seed is significant. Reducing escapes at the end of the season will take an entire system approach for each trait platform.


Products like Engenia® and XtendiMax® will be very effective on waterhemp, marestail, and giant ragweed. One advantage compared to other post-emergence platforms is the soil activity provided with Engenia and XtendiMax. How effective is the post-emergence activity? PFR data has shown that Engenia plus Roundup PowerMAX® resulted in 94% and 98% control of waterhemp and fall panicum 35 DAT, respectively.

What about a systems approach? Utilizing Authority® Elite as a pre-emergence herbicide alone resulted in 63% control of waterhemp and 65% control of fall panicum at the end of the season. However, when Authority Elite was followed by Engenia and Roundup PowerMAX plus DRA (post-emergence), it resulted in 87% control of waterhemp and 88% control of fall panicum at the end of the season. The addition of Warrant® as a post-emergence application, resulted in a 5% increase in waterhemp control at the end of the season.

Can I be successful without dicamba in the post-emergence trip?

Using XtendiMax or Engenia in the pre-emerge will result in very effective post-emergence control. What are the options in season without dicamba in the post-emergence trip? Products that contain fomesafen such as Flexstar®, as well as other PPOs such as Cobra®, or Ultra Blazer® could be used for waterhemp control. However, some populations may be resistant to PPOs in the post-emergence trip, making the pre-emerge very important. The success of the pre-emerge depends on rainfall for activation and how much rain occurs throughout the season. Utilization of in-season residuals will be crucial, especially since Group 15s provide very effective waterhemp control.

Planting early to ensure early canopy closure is another key to success. The pictures on the next page showcase how early planted soybeans with a successful pre-emerge still provided successful weed control at the end of the season, even though the population is suspected to be resistant to Cobra and glyphosate. However, the Roundup Ready 2 Xtend® system provides flexibility for other control options thanks to XtendiMax and Engenia. If the residuals would fail, a post-emergence application of XtendiMax or Engenia can be used to control any weeds that have escaped if PPO or glyphosate-resistant waterhemp is a concern.


Farmers have access to two formulations of 2,4-D choline in this system: Enlist One® (2,4-D choline) and Enlist Duo® (2,4-D choline plus glyphosate). Enlist One applied at 32 oz. resulted in 82% waterhemp control by 35 DAT. Enlist One plus glyphosate or Enlist One plus Liberty® resulted in 91% and 95% waterhemp control by 35 DAT, respectively.

How effective is the Enlist system? At the end of the season, Authority® Elite followed by Enlist One resulted in 83% control of waterhemp and 81% control of fall panicum. Waterhemp control increased by adding glyphosate (+12% control) or Liberty (+13% control). Similarly, fall panicum control also increased when Enlist One was combined with glyphosate (+15% control) and Liberty (+10% control). When an in-season residual such as Warrant® was added, waterhemp control was 98% and fall panicum control was 91%. In heavy waterhemp pressure or if marestail is present, consider adding Liberty to Enlist One (1:1 ratio; 32 oz.) for more effective control.


LibertyLink® GT27™ soybeans have tolerance to glyphosate and Liberty. If many of the problematic weeds are resistant to glyphosate, what is the advantage if Liberty is so effective? For weeds such as velvetleaf and grasses, glyphosate will still provide control, thus broadening the weed control spectrum versus Liberty alone.

If Liberty is tank mixed with glyphosate, you should manage it exactly like a Liberty application but mix it at a 1:1 ratio with the glyphosate. Glyphosate will increase Liberty control, especially in morning and evening applications. For best control, applications should be targeted for the heat of the day, even if glyphosate is mixed with Liberty.

Beck's offers the LibertyLink GT27 platform in our Freedom Plus® soybean series.

WANT MORE ON SOYBEAN HERBICIDE PROGRAMS? Beck's 2020 Recommended Soybean Herbicide Programs Brochure will be available at Beck's PFR Insight Meetings starting in January 2020. See page four for more information.

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Author: Joe Bolte

Categories: CropTalk, 2019


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