A fast-spreading plague of "super weeds" taking over U.S. farmland will not be stopped easily, and farmers and government officials need to change existing practices if food production is to be protected, industry experts said on Thursday.

"This is a complex problem," said weed scientist David Shaw in remarks to a national "summit" of weed experts in Washington to come up with a plan to battle weeds that have developed resistance to herbicides.

A new biotech corn developed by Dow AgroSciences could answer the prayers of U.S. farmers plagued by a fierce epidemic of super-weeds. Or it could trigger a flood of dangerous chemicals that may make weeds even more resistant and damage other important U.S. crops.

Or, it could do both.

A coalition of more than 2,000 U.S. farmers and food companies said Wednesday it is taking legal action to force government regulators to analyze potential problems with proposed biotech crops and the weed-killing chemicals to be sprayed over them.

The Environmental Protection Agency on Monday said that the widely used herbicide 2,4-D would remain on the market, denying a petition from an environmental group that sought to revoke the chemical’s approval.

The E.P.A. said that the environmental group, the Natural Resources Defense Council, had not adequately shown that 2,4-D would be harmful under the conditions in which it is used.

“At best, N.R.D.C. is asking E.P.A. to take a revised look at the toxicity of 2,4-D,” the E.P.A. said in its decision, which was posted on its Web site.

Scientists, environmentalists and farm advocates are pressing the question about whether rewards of the trend toward using more and more crop chemicals are worth the risks, as the agricultural industry strives to ramp up production to feed the world's growing population.

The debate has heated up in the last several weeks, with a series of warnings and calls for government action including a lawsuit against the U.S. Environmental Protection Agency.

Monsanto Co said on Friday that it had settled a long-running legal battle with residents of West Virginia who claimed they suffered environmental and health problems tied to pollution from a former Monsanto chemical plant.

St. Louis-based Monsanto, which has shifted from a concentration in the chemical business to agricultural seeds, said it would commit to more than $90 million in clean-up, remediation and medical monitoring to resolve a series of class action lawsuits involving a plant once located in Nitro, West Virginia.

The United States remained the primary backer of biotech crop technology in 2011, but adoption spread internationally as the total global planted area of genetically modified seeds grew 8 percent from a year ago, according to a report issued Tuesday.

Roughly 160 million hectares, or 395.2 million acres, were planted with biotech crops in 2011, up 8 percent from 2010, said the International Service for the Acquisition of Agri-Biotech Applications (ISAAA) in its annual report on biotech seed use.