By Carey Gillam

(Reuters) - The Environmental Protection Agency gave final approval on Wednesday to a new herbicide developed by Dow AgroSciences that has faced broad opposition, ordering a series of restrictions to address potential environmental and health hazards.

EPA said it was applying "first-time-ever restrictions" on its approval of the herbicide, called Enlist Duo, which is designed to be used with new genetically modified crops developed by Dow AgroSciences, a unit of Dow Chemical.

The herbicide was developed by Dow as an answer to severe weed resistance problems that are limiting crop production around the country.

EPA said the approval lays out a template of new requirements for future approvals of herbicides designed for use with genetically modified crops.

Dow will be required to closely monitor and report to EPA to ensure that weeds are not becoming resistant to Enlist Duo, the agency said. As well, EPA is ordering a 30-foot in-field “no spray” buffer zone around application areas. It has also banned use when wind speeds are over 15 miles per hour.

Initially, Enlist Duo will be allowed only in Illinois, Indiana, Iowa, Ohio, South Dakota and Wisconsin. EPA will take public comments until Nov. 14 about approving the product for use in Arkansas, Kansas, Louisiana, Minnesota, Missouri, Mississippi, Nebraska Oklahoma, Tennessee and North Dakota.

EPA will review its approval of Enlist Duo in six years rather than the usual 15 years.

The EPA decision comes after the U.S. Department of Agriculture gave final approval last month to Enlist corn and soybeans, which have been altered to tolerate being sprayed with Enlist Duo herbicide. The specialty crops and the herbicide are to be sold as a branded "Enlist Weed Control System".

Like the popular Roundup Ready system developed by rival Monsanto Co, farmers who plant Enlist crops can spray over the crops in their fields with Enlist herbicide and kill weeds but not the crops.

Heavy use of Roundup herbicide triggered an explosion of herbicide-resistant "super weeds" that are hard for farmers to fight and which can choke off crop yields. Such weeds now infest roughly 70 million acres of U.S. farmland, according to Dow.

Enlist Duo combines a 60-year-old herbicide component known as 2,4-D with glyphosate, the chief ingredient in Roundup. Using the 2,4-D in combination with glyphosate should help farmers kill weeds that are resistant to Roundup, Dow officials say. Dow pegs the market for Enlist at about $1 billion, and hopes to start selling the system for the 2015 U.S. spring planting season.

There has been broad opposition to Enlist Duo. Critics say use of 2,4-D has been linked to a range of health problems, including reproductive problems, non-Hodgkin's lymphoma and Parkinson’s disease. They also fear the new herbicide could drift into neighboring farm fields, harming crops there. And they say that in the long run it will only increase weed resistance problems.

The EPA received more than 400,000 comments about Enlist Duo. In one letter, dated June 30, 2014, the Environmental Working Group nonprofit advocacy organization listed the names of more than 77,000 people asking EPA to deny approval.

But the EPA said its scientists used "highly conservative and protective" assumptions to evaluate the human health and ecological risks of Enlist Duo and that usage as approved will protect the public, agricultural workers, and endangered species. 

The agency said it evaluated the risks to all age groups, from infants to the elderly, and took into account exposure through food, water, pesticide drift, and as a result of use around homes.

"Our decision reflects sound science... and is protective of everyone and the environment," said Jim Jones, assistant administrator for EPA's Office of Chemical Safety and Pollution Prevention.



(Reporting by Carey Gillam in Kansas City; Editing by Peter Galloway)