The Environmental Protection Agency today gave the green light to an herbicide designed for use with new genetically modified corn and soybeans.

Dow AgroSciences’ Enlist Duo contains a new formulation of 2,4-D, a weed killer that’s been around for decades. Last month, the U.S. Agriculture Department approved new corn and soybeans to be used in concert with the new herbicide.

The new products come in the face of an increase in weeds that have become resistant to glyphosate. Monsanto introduced “RoundUp Ready” seeds in the 1990s that were engineered to resist glyphosate. Farmers could spray their fields kill the weeds, but not the crops.

But today, some 70 million acres of farmland contain weeds that have grown to resist glyphosate. The problem is worst in southern states, but has quickly crept north into the nation’s corn and soybean belts. Mike Owen, a weed expert at Iowa State University, told NewsHour he estimates 70 to 75 percent of Iowa’s soybean fields contain a resistant weed called waterhemp. Farmers have complained they lack the tools to contain the problem.

Environmental groups and public health advocates vehemently opposed the approval of the new Dow products. They say the new products will greatly increase the use 2,4-D and point to research showing a correlation between pesticides and non-Hodgkin’s lymphoma, Parkinson’s disease and reproductive problems. Opponents also argue the herbicide could drift and harm other crops, and could lead to a new generation of herbicide-resistant weeds. The Center for Food Safety has threatened legal action to stop the sale of the products, which could hit the market early next year.

The EPA, which received more than 400,000 comments, announced it was placing “first time ever” restrictions on the products. They include requirements for close monitoring by Dow, buffer zones and spraying restrictions in windy conditions. EPA will also review its decision in six years instead of the usual 15 years, and has only approved the products for use in six states (Illinois, Indiana, Iowa, Ohio, South Dakota and Wisconsin). Ten more states could gain approval pending a comment period that ends November 14.

Dow AgroSciences today applauded the decision and estimates the new products could double earnings for the company in the next five to seven years, according to Bloomberg News.