WASHINGTON - The Agriculture Department has approved the use of genetically modified corn and soybean seeds that are resistant to a popular weed killer.

However, farmers won't be able to take full advantage of the seeds until the Environmental Protection Agency issues a second ruling allowing the use of Enlist, a new version of the 2,4-D weed killer that's been around since the 1940s. The EPA has said it will rule this fall on Dow AgroSciences' application to market the chemical.

The agriculture industry has been anxiously awaiting the approvals, as many weeds have become resistant to glyphosate, an herbicide commonly used on corn and soybeans now. Herbicide-resistant seeds introduced in the 1990s allowed farmers to spray fields after their plants emerged, killing the weeds but leaving crops unharmed.

Critics say they are concerned the increased use of 2,4-D could endanger public health and that more study on the chemical is needed. The USDA has said that if both the seeds and herbicide are approved, the use of 2,4-D could increase by an estimated 200 per cent to 600 per cent by the year 2020.

While the Agriculture Department only oversees the safety of the plants, the EPA oversees the safety of the herbicide for human and environmental health. The agency already has found the chemical safe for the public and agricultural workers.

The department on Wednesday said it had decided to approve the seeds in an online posting first reported by Politico.

Groups lobbying the agency to prevent the herbicide's expanded use say they are concerned about the toxic effects of the herbicide and the potential for it to drift. Corn and soybeans are the nation's largest crops, and the potential for expanded use is huge.

"With this approval comes millions of more pounds of toxic herbicides dumped onto our land. It's an unacceptable outcome," said Andrew Kimbrell, executive director for Center for Food Safety.

Dow AgroSciences says the new version has been re-engineered to solve potential problems, like drift before and after the herbicide hits the plant.

The weed killer 2,4-D is now used on other crops, including wheat, and on pastures and home lawns. It is the world's most popular herbicide and the third most popular in the United States, behind atrazine and glyphosate.

If approved, the new version of 2,4-D would be used in combination with glyphosate.

___

Follow Mary Clare Jalonick on Twitter: http://twitter.com/mcjalonick

News from © The Associated Press, 2014