Published on Wednesday, December 7, 2016
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.
Graph 1. 2015 herbicide system soybean yield data from Southern IL.Corrected to 13% moisture. Individual results may vary.
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.
Though we did not see an increase in yield from the use of Anthem Maxx, we did see optimum waterhemp control. An in-season residual is crucial for weed management. Anthem Maxx has two components, a group 14 and group 15 herbicide. The group 14 helps control the new flush of waterhemp that emerged after the Authority Assist lost effectivity. The group 15 provided in-season residual control after the Authority Assist activity was minimized. This resulted in a waterhemp barrier until the crop canopy closed. When it came to fall panicum control in the Roundup system, Authority Assist resulted in 80 percent control. Thanks to the activity from the Authority Assist, this reduced the pressure of fall panicum on the POST application. The application of Roundup was able to control the fall panicum that broke through the Authority Assist and resulted in 100 percent control. Anthem Maxx was not needed for fall panicum control where Roundup was effective.
Graph 3. Visual control of waterhemp and fall panicum in the Roundup Ready 2 Yield system at harvest in 2016. Individual results may vary.
When it comes to weed control in the LibertyLink system, Liberty alone resulted in effective control of waterhemp (Graph 4) that was emerged at the time of application, but did not result in season-long control. Since Liberty does not offer residual control, there was no barrier to prevent the new emergence of waterhemp. A single application of Liberty resulted in 53 percent control, however, two applications of Liberty resulted in 90 percent control. The R2 application controlled the waterhemp that emerged after the V4 application. When Authority Assist was added to Liberty, waterhemp control increased to 100 percent.
So this brings up a question, do we need a POST residual or a PRE application in a Liberty system? Though waterhemp can be controlled with two applications of Liberty, this is only a temporary solution. Once again, we did not see a yield advantage when using residuals. However, the residuals did reduce the waterhemp population that Liberty had to control. Thanks to Authority Assist, the number of waterhemp weeds that emerged prior to the V4 application were also reduced. With the use of Anthem Maxx, the waterhemp that had already emerged was controlled, and it provided an in-season residual which held back the waterhemp until the canopy closed. The use of PRE and POST added four more active ingredients and three more modes of action. Multiple modes of action can help control waterhemp that may have escaped from the Liberty application, reducing the chance for the development of weed resistance. Also, with more actives and more modes of action, the weed control spectrum is broadened. This helps explain the increase in herbicide efficacy of fall panicum with the addition of Authority Assist. Authority Assist alone resulted in greater fall panicum control versus a single application of Liberty. When Authority Assist and Liberty were added together, control increased to 95 percent. However, when adding two more actives from the Anthem Maxx, control increased to 100 percent.
Graph 4. Visual control of waterhemp and fall panicum in the LibertyLink system at harvest in 2016. Individual results may vary.
With the lower commodity prices, you may be asking yourself “what can I do to cut costs?” Though complex herbicide programs may not show an advantage on the yield monitor, they do have an advantage when it comes to weed control. You may also be asking yourself how you can manage waterhemp in a Roundup system. Having clean fields is still possible with the Roundup system, but having multiple modes of action is crucial for the success of weed management. In this system, a PRE that controls glyphosate-resistant weeds such as waterhemp is imperative. However, with wet springs and faster break down of pre-emerge herbicides, an in-season residual is crucial to hold back weeds until full canopy closer. When it comes to the Liberty system, two applications of Liberty alone resulted in effective weed control. However, this is a temporary solution to a long term problem. A use of a PRE will broaden the weed control spectrum and allow more modes of action. The use of Anthem Maxx helps not only the POST control of weeds with the Liberty, but also provides an in-season residual. The POST residual is not as crucial in the Liberty system as it is to the Roundup system. Multiple modes of action will help extend the lifespan of the current herbicides on the market.
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.
Author: Joe Bolte
Categories: PFR, PFR Reports
Tags: Practical Farm Research, LibertyLink, PFR, Waterhemp, herbicides, Liberty, weed resistance, glyphosate, Roundup Ready 2 Yield, Roundup, Anthem, Warrant, Anthem Maxx, Roundup PowerMAX, panicum