Dow Corn, Resistant to a Weed Killer, Runs Into Opposition

“The leaves had curled and the plants were kind of twisting rather than growing straight,” Mr. Herr said of the 2009 incident on his vegetable farm in Lowell, Ind. He is convinced the chemical, as well as another herbicide called dicamba, had wafted through the air from farms nearly two miles away.

Mr. Herr recalled the incident because he is concerned that the Dow Chemical company is on the verge of winning regulatory approval for corn that is genetically engineered to be immune to 2,4-D, allowing farmers to spray the chemical to kill weeds without harming the corn stalks.

That would be a welcome development for corn farmers like Brooks Hurst of Tarkio, Mo., who are coping with runaway weeds that can no longer be controlled by Roundup, the herbicide of choice for the last decade.

But some consumer and environmental groups oppose approval of Dow’s corn, saying it will lead to a huge increase in the use of 2,4-D, which they say may cause cancer, hormone disruption and other health problems. They are being joined by a coalition of fruit and vegetable farmers like Mr. Herr and canners like Red Gold and Seneca Foods, which filed petitions with the government last week seeking a delay in the corn’s approval.

The Save Our Crops Coalition, as it calls itself, says it is not opposed to biotechnology. But it fears that fruits and vegetables, which will not be immune to 2,4-D, will become unintended casualties of herbicide drift as the chemical is sprayed on tens of millions of acres of corn.

The dispute is the latest iteration in the intense and often bitter battle over genetically modified crops, made even more emotional in this case because of the connection between 2,4-D and Agent Orange, the notorious defoliant that has been linked to birth defects, cancer and other health problems in Vietnamese civilians and American veterans.

Some opponents of Dow’s product call it “Agent Orange corn.” Dow and its allies call that a misleading scare tactic.

The victims of Agent Orange do not deserve “to have their tragedy exploited in an irresponsible way,” Steve Savage, an agricultural consultant wrote in his blog, Applied Mythology.

Most experts agree that the harm from Agent Orange was caused primarily by its other ingredient, 2,4,5-T, which was taken off the market long ago. By contrast, 2,4-D, first approved in the late 1940s, is considered safe enough for use in many home lawn care products.

The Environmental Protection Agency, after repeated reviews, continues to say that there is not enough evidence to call 2,4-D a human carcinogen. This month, the agency rejected a petition from the Natural Resources Defense Council seeking the removal of 2,4-D from the market on health and safety grounds.

The Agriculture Department is leaning toward approval of the 2,4-D-resistant corn, according to its draft environmental assessment. But it is accepting public comments until Friday, and has already received more than 5,000. Opponents say that 267,500 people have signed a petition asking the government to deny Dow’s request.

Dow hopes the approval will come in time for planting next year.

For farmers like Mr. Hurst, the approval couldn’t come too soon. “I think it’s a crisis, and we need something to have a solution to get rid of resistant weeds,” Mr. Hurst said. He said that without new chemical approaches, farmers would have to plow more, increasing soil erosion.

The corn is just the first of a new wave of herbicide-tolerant crops. Dow is also developing soybeans and cotton immune to 2,4-D. Close behind, Monsanto is developing soybeans, cotton and corn that can tolerate dicamba, another old herbicide in the same family as 2,4-D. Bayer, Syngenta and DuPont are developing crops resistant to other herbicides. too.

Of the 20 genetically engineered crops awaiting approval, 13 are intended to be resistant to one or more herbicides.

The activity stems from the huge success, at least initially, of Monsanto’s Roundup Ready crops, which are genetically engineered to tolerate its herbicide Roundup, also sold generically as glyphosate.

Those crops made it so easy for farmers to control weeds by spraying glyphosate that Roundup Ready crops now account for about 90 percent of soybeans and around 70 percent of the corn and cotton grown in the United States. And use of glyphosate skyrocketed, at the expense of rival herbicides.