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Crop Roundup: EPA Announces Proposed Decision to Register Enlist Duo

The EPA announced its proposed decision to register Enlist Duo. Western corn rootworm resistance spreads, and mixing sites of action is key to fighting herbicide resistance, say experts.

Enlist Duo reaches milestone in the regulatory review process
The Enlist Weed Control System from Dow AgroSciences has reached another milestone in the regulatory review process. The U.S. Environmental Protection Agency (EPA) announced its proposed decision to register Enlist Duo. Enlist Duo is the herbicide for use with
the Enlist system.

The EPA also opened a 30-day comment period, giving growers and others an opportunity to provide input on Enlist Duo herbicide before the agency makes its final registration decision.

Enlist Duo is a proprietary blend of new 2,4-D choline and glyphosate. By combining two modes of action, Enlist Duo will control and help prevent further development of herbicide-resistant weeds. The herbicide features Colex-D Technology, which will provide stewardship and user benefits, including minimized potential for physical drift, ultra-low volatility, reduced odor, and better handling characteristics.

“In its review, the EPA acknowledged the significant scientific advancements Dow AgroSciences made with Enlist Duo herbicide as it relates to off-target movement,” says Damon Palmer, U.S. commercial leader for Enlist, Dow AgroSciences. “Enlist Duo herbicide will help solve the tremendous weed control challenges that growers are facing, and it will do so with technology optimized for on-target application.”

In its “Proposed Registration of Enlist Duo Herbicide” released earlier this week, EPA says it has a “full and scientifically robust data set on 2,4-D” with respect to human health. Regulatory agencies in more than 70 countries, including the United Kingdom, Germany, France, Canada, Japan, Australia and the U.S., have authorized the use of 2,4-D since 2001 using modern regulatory requirements.

The draft label for Enlist Duo includes proposed registration for Iowa, Illinois, Indiana, Ohio, South Dakota, and Wisconsin. Dow AgroSciences is working with the EPA to expand the list of states in time for the technology’s launch.

Enlist Duo herbicide tailored for modern agriculture
Grower and applicator usability was a primary consideration for Dow AgroSciences in the development of Enlist Duo herbicide. In addition to company and university testing, the first grower-led research plots for the Enlist Weed Control System were conducted in 2013.

“For Enlist to be a preferred solution on the farm, it has to be a modern solution — one that advances the farming practices of today,” Palmer says. “The results from this on-farm research activity were consistent with our data, and confirmed that the technology consistently performs in real-world scenarios.”

The research plot participants rated Enlist Duo in the highest percentile (90% to 100%) for broadleaf and grass weed control across all plots. These growers were also asked to evaluate the drift and volatility potential of Enlist Duo herbicide with Colex-D Technology. Lab and in-field research has shown that using Enlist Duo with Colex-D Technology in combination with a low-drift spray nozzle can decrease physical drift by up to 90% when compared with a tank mix of glyphosate and traditional 2,4-D sprayed through a standard XR nozzle. The new Enlist Duo also will have up to 96% reduction in volatility compared with traditional 2,4-D products.

Growers participating in the research plots noted the improvements related to off-target movement that they experienced in their trials. “We had Enlist corn planted next to some soybeans. With the constant 6-mph wind and the gusts, we could lay Enlist Duo next to the soybeans, and I see no crinkling of the leaves, I see no drift,” says Doug Morrow, Indiana grower and research plot participant.

Resources for responsible use
With the launch of Enlist, growers and retailers will have access to a benefits-based management resource called Enlist Ahead. Enlist Ahead will provide best-management recommendations to complement the herbicide label requirements, including the use of a residual, soil-applied preemergence herbicide for weed-resistance management.
Pending regulatory approvals, Dow AgroSciences expects to launch Enlist corn and Enlist soybeans in 2015, with Enlist E3 soybeans and Enlist cotton to follow.

For additional information about the Enlist Weed Control System, visit Enlist.com.

Cry3Bb1 WCR Resistance
The western corn rootworm has developed resistance to the first genetic modifications intended to battle the bug. And resistance is continuing to spread. Watch this video for more information. 

Site of action key to herbicide effectiveness
Weed control today is more complex and difficult than it was for past generations. Not only do today’s growers need to prepare to face difficult weeds, an increasing number also face herbicide resistance. In fact, three out of four growers who participated in a recent BASF survey suspect that glyphosate resistance is a cause of tough-to-control weeds. A key element to combating resistance is the herbicide site of action.

Herbicide-resistant weeds became a problem when growers depended on a single-herbicide program over a long period of time without supplementing any significant cultural practices, such as tillage. As the same herbicide was applied year after year, weeds were progressively selected for resistance because only one herbicide site of action was used.

Many wonder about the difference between site of action and mode of action. The site of action is the location within the plant where the herbicide impacts the development process. The mode of action is the name for the process the herbicide uses to control the weed. So site of action is “where” and mode of action is “how.”

“The site of action is the location in the plant where the herbicide has its primary effect,” said Bryan Young, associate professor of weed science, Purdue University. “Typically, the target is an enzyme used in carrying out a process like amino acid production or photosynthesis. The herbicide targets that enzyme and stops the process.”

Though sites of action can be referred to by the protein function they inhibit, such as acetolactate synthase (ALS) or p-hydroxyphenylpyruvate dioxygenase (HPPD), they are also grouped numerically based on their function. For example, an ALS herbicide that inhibits amino acid synthesis is labeled as Group Two. This group label is always listed on the product label.

Today, resistance exists to glyphosate, ALS, and triazine.

“Because it is the key to a herbicide’s effectiveness, we recommend using a variety of effective sites of action,” said Chad Brommer, biologist, herbicides at BASF. “Utilizing different sites of action is like having multiple tools in your weed control tool belt.”

There are about two dozen sites of action registered today for commercial products. About half of those are available in the U.S. Because of the limited number of available sites of action and the spread of weed resistance, it’s important to use overlapping effective sites of action to reduce selection pressure on any single site of action and mitigate the development of further resistant populations.

“One way to combat resistance is through rotation and diversification,” said Young. “Even if crops are rotated from year to year, the goal should be to use a diverse combination of herbicide sites of action each year with minimal overlap of any single site of action between years in the same field.”

For improved weed management, use more than one site of action and rotate herbicide usage to control weeds and prevent resistance.

Sources: Dow AgroSciences, University of Illinois, BASF

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