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PFR Report

The Efficacy of Herbicide Modes of Action in Roundup Ready® and LibertyLink® Systems

Published on Wednesday, January 4, 2017

In agriculture, we are always looking for the next new tool or management practice that will allow us to become even more successful. When it comes to weed control, new opportunities are very limited even though new trait technologies are either on the market or pending approval. In the past few years, there has been a limited release of new herbicide active ingredients. It’s been almost two decades since a new mode of action has been released. With fewer herbicide modes of action and active ingredients available, weed control has become even more challenging than in past years. 

One approach to managing hard-to-control weeds is to combine herbicide active ingredients that are already on the market to create a program with multiple modes of action. This approach can help answer questions like “Can I still be successful in a Roundup Ready® system?” and “How should I manage the LibertyLink® system to prevent resistance?”

In 2016, Beck’s Practical Farm Research (PFR)® evaluated the ADAMA’s Five X 5 system in both a Roundup Ready and LibertyLink scenario at our Southern Illinois PFR site. The Five X 5 system compares five modes of action to two modes of action, in an attempt to showcase the strengths and weaknesses of different herbicide active ingredients. This study also included other forms of the same active ingredient from different companies. The Five X 5 system strategically uses active ingredients that have been on the market for many years. Some of these products have both pre-emergence (PRE) and post-emergence (POST) activity on weed control, so application timing is crucial. The Five X 5 system takes advantage of products that contain PRE and POST activity as well as products that just have residual or POST activity. 

Figure 1. Herbicide Groups, Active Ingredients and Manufacturers

To evaluate the effectiveness of PRE herbicides, ratings (shown in Figure 7) were taken 28 days after treatment (DAT) prior to any POST applications. These ratings were averaged across both the Roundup and Liberty® systems. The two principal weeds in this study were waterhemp and yellow foxtail. The waterhemp at this location has believed to be resistant to glyphosate, the active ingredient in Roundup WeatherMAX®. This weed population has also believed to be resistant to Group 2 (ALS) herbicides such as Classic®
(chlorimuron-ethyl) and Pursuit® (imazethapyr). 

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