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Sponsored: Glyphosate Tolerant vs. LibertyLink Systems

One question that farmers are faced with each year is how they should manage their soybean herbicide program. With multiple herbicide systems on the market and the possibility of new traits becoming available, the decision becomes more difficult. Lower commodity prices make it even more challenging to justify the cost of an in-season residual such as Anthem® or Warrant®. However, as herbicide resistance continues to increase, it’s crucial to manage weeds that escape other herbicide applications. For the past two years, Beck’s Southern Illinois Practical Farm Research (PFR)® team has tested different management options with both the glyphosate tolerant (Roundup) and LibertyLink® systems. In this study, we looked at several different application variations including: pre-emergent (PRE) alone, post-emergent (POST) alone, PRE and POST combined, as well as an in-season residual.

Overall, the POST-only treatments out-yielded treatments with Authority® Assist, Anthem, Anthem® Maxx and Warrant (Graph 1 and 2). We have faced cool, wet conditions over the last two years in southern Illinois which has resulted in PPO (Group 14) injury from the Authority Assist. This PPO injury early in the season resulted in thinner stands and lower yields compared to POST-only treatments. In both years, Authority Assist followed by Liberty® yielded less than a single or dual application of Liberty. In 2016, Roundup alone resulted in higher yields than expected and the Authority Assist application followed by Roundup increased yield by 2 Bu./A. compared to Roundup alone. In both years, there was no distinct yield advantage with the use of an in-season residual compared to POST-only treatments. There was also no clear yield increase advantage with an in-season residual compared to just using a PRE followed by Liberty or Roundup. 

12.8_Herbicide Systems_Graph 1

Graph 1. 2015 herbicide system soybean yield data from Southern IL. Corrected to 13% moisture. Individual results may vary.

12.8_Herbicide Systems_Graph 2

Graph 2. 2016 Herbicide System soybean yield data from Southern IL. Corrected to 13% moisture. Individual results may vary.

When it comes to evaluating a herbicide program, yield only tells part of the story. In 2016, herbicide ratings were taken at harvest to evaluate the effectiveness of season-long weed control (Graph 3). In this study, waterhemp and fall panicum were the main weeds we observed. This population of waterhemp is believed to be resistant to glyphosate, the active ingredient in Roundup. Though POST treatments alone yielded well, they had a distinct disadvantage when it came to weed control, especially in the Roundup system. Single or double applications of Roundup resulted in less than 50 percent control of waterhemp. 

Authority Assist resulted in greater waterhemp control compared to Roundup alone. Authority Assist, applied alone, resulted in less than 60 percent control of waterhemp at harvest. It offered exceptional weed control up to V4, but was less effective as the season went on.  Prior to canopy closure, Authority Assist allowed new flushes of weeds to emerge before the canopy closed. Adding POST applications can increase the herbicide efficacy when it comes to having clean fields at harvest time. When Authority Assist was added with a POST application of Roundup, waterhemp control increased to 95 percent. When the POST residual of Anthem Maxx was added, control increased to 98 percent.

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Joe Bolte | Beck's Southern Illinois PFR Operator 

For more PFR Agronomic Updates from Joe Bolte, please visit his blog on BecksHybrids.com.

 

Practical Farm Research (PFR)® is a registered trademark of Beck’s Superior Hybrids, Inc. Liberty® and LibertyLink® are registered trademarks of Bayer. Warrant®, Roundup Ready 2 Yield® and Roundup PowerMax® are registered trademarks of Monsanto Technology, LLC. Anthem® and Authority® brands are registered trademarks of FMC Corporation.

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