By Amit Jhala, Extension Weed Management Specialist
The evolution of glyphosate-resistant weeds is a concern for successful corn and soybean production.
In Nebraska, for example, six weed species have been confirmed resistant to glyphosate: common ragweed, giant ragweed, common waterhemp, kochia, marestail, and Palmer amaranth.
Crops with multiple-herbicide tolerances, including dicamba- plus glyphosate-resistant Roundup Ready 2 Xtend soybean, have been developed, tested, and approved. This new dicamba-tolerant soybean cultivar, expected to be planted on over 15 million acres in 2017, offers an additional means of managing herbicide-resistant weeds.
Special low-volatile dicamba herbicide formulations have been developed for use with this cultivar. They are Roundup Xtend (a premix of glyphosate and dicamba; pending EPA approval) and XtendiMax (dicamba).
They will be labeled for use before, at, and after planting Roundup Ready 2 Xtend Soybean. Moreover flexibility in applying XtendiMax may allow growers to make pre- or post-emergence applications on dicamba-tolerant crops to manage glyphosate-resistant weeds and maximize crop yield potential.
In addition, product stewardship programs are expected to help ensure the successful application of XtendiMax to minimize off-target movement; however, no research data is currently available of landscape level effect of volatility from this new formulation of dicamba.
This registration is for a formulation of dicamba that contains an additive that reduces volatility and is different from products that were alleged to have been used illegally in the 2016 growing season in several states.
Figure 1. Control soybean plot with no herbicide treatment. (Photos by Amit Jhala)
Figure 2. Roundup Ready 2 Xtend soybeans where Rovel was applied pre-emergence followed by XtendiMax applied post-emergence.
The dicamba formulation for use on dicamba-tolerant soybean has been registered for sale and use in Alabama, Arizona, Arkansas, Colorado, Delaware, Florida, Georgia, Illinois, Iowa, Indiana, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Virginia, West Virginia, and Wisconsin.
Related Nebraska Research
Research conducted at UNL’s South Central Agricultural Lab near Clay Center the last four years showed excellent weed control and crop safety with a pre-emergence herbicide applied at planting followed by post-emergence application of XtendiMax in Roundup Ready 2 Xtend soybean (Figures 1 and 2).
The label requires very specific drift mitigation measures, including:
- no aerial application,
- no application when wind speed is over 15 miles per hour;
- application only with approved nozzles at specified pressures; and
- buffer zones to protect sensitive areas when the wind is blowing toward them.
Weeds can evolve resistance to any herbicide if the same herbicide is applied repeatedly in the same field. For example, dicamba-resistant kochia has been confirmed in western Nebraska.
Therefore, growers should not rely only on XtendiMax for weed control in Roundup Ready 2 Xtend soybean. Pre-emergence herbicide is a foundation for weed control in any type of soybean. Select a weed management program that includes herbicides with multiple effective modes of action.
For more information about the EPA registration of XtendiMax with Vapor Grip Technology, a feature marketed by the industry to reduce off-target drift, see the related EPA news release, EPA Registers Dicamba Formulation for Use on Dicamba Tolerant Crops.
