The U.S. Environmental Protection Agency (EPA) is registering Enlist Duo, a herbicide that contains 2,4-D and glyphosate, with first-time ever restrictions to manage the problem of resistant weeds.

The pesticide is used to control weeds in corn and soybeans that are genetically-engineered to tolerate 2,4-D and glyphosate.

According to the EPA, its decision reflects a large body of science and an understanding of the risk of pesticides to human health and the environment.

The approved formulation contains the choline salt of 2,4-D which is less prone to drift than the other forms of 2,4-D. In addition, restrictions on its use are intended to avoid pesticide drift, including a 30-foot in-field "no spray" buffer zone around the application area. No pesticide application is allowed when the wind speed is over 15 mph, and only ground applications are permitted.

As part of efforts to ensure that weeds will not become resistant to 2,4-D, the EPA is also imposing new requirements on the registrant. These requirements include extensive surveying and reporting to the EPA, as well as grower education and remediation plans.

In six years' time the registration will expire, allowing the EPA to revisit the issue of resistance.

The EPA said that in the future it intends to apply this approach to weed resistance management for all existing and new herbicides used on herbicide tolerant crops.

For the moment, the EPA is registering the pesticide in six states: Illinois, Indiana, Iowa, Ohio, South Dakota and Wisconsin. It is accepting comments until mid-November on whether to register Enlist Duo in ten more states: Arkansas, Kansas, Louisiana, Minnesota, Missouri, Mississippi, Nebraska, Oklahoma, Tennessee and North Dakota.