Approved by the EPA just over a year ago for use on genetically modified corn and soybeans, Enlist Duo is now in danger of becoming illegal to use.

In a dramatic, and potentially far-reaching reversal of opinion, the Environmental Protection Agency asked a federal court to remove Dow AgroSciences' Enlist Duo from the market, citing that the agency originally, "did not have all relevant information at the time it made its registration decision."

The EPA had approved Enlist Duo just over one year ago for use on genetically modified corn and soybeans according to the Natural Resources Defense Council, which sued to challenge that approval. The environmental agency is now abandoning its defense of that decision in court.

The pesticide combines glyphosate, the same active ingredient as in Roundup, with another weed killer called 2,4-D. In its court filing, the EPA said that when it registered Enlist Duo, it had overlooked the "synergistic effects" of the pesticide's chemicals on plants growing outside treated farm fields, especially plants that are endangered. EPA is now concerned that the pesticide is far more toxic than the agency first concluded based on an incomplete review.

According to the NRDC, glyphosate is the most widely used weed killer in the country, and is the chief cause of the decline of the monarch butterflies. The organization also argues that scientists have raised serious questions about 2,4- D's impact on human health.

"Removing this dangerous chemical from the market is a key step in protecting sensitive native plants and monarch butterflies, which have been further threatened by its impact on milkweed, the plant they need to survive," stated Sylvia Fallon, senior scientist at the NRDC. ""We are delighted by this news, but also troubled that EPA overlooked this information initially. Regulators need to get it right the first time and take the time necessary to make reasoned, deliberate decisions."

Previously, more than 200,000 people signed an NRDC petition asking Dow AgroSciences to cancel its plans to sell Enlist Duo. The company has until Dec. 7 to respond and then it will be up to the court to decide the pesticide's fate.