An EPA spokeswoman declined to give specifics of the plan, but has indicated that its requirements will be similar to those placed on a new herbicide product developed by Dow AgroSciences, including weed monitoring, farmer education and remediation plans. The company is required to provide extensive reporting to the EPA about instances of weed resistance and to let "relevant stakeholders" know about the difficulties of controlling them via a company-established website.

At least 14 weed species and biotypes in the United States have developed glyphosate resistance, affecting more than 60 million acres of U.S. farmland, according to data gathered by the U.S. Department of Agriculture and U.S. weed scientists. The herbicide-resistant weeds hinder crop production and make farming more difficult and expensive.

The EPA's action comes in the wake of a finding by the World Health Organization's cancer research unit this month that glyphosate is "probably carcinogenic to humans," a conclusion the working group said was based on a review of years of scientific research. Testing has found residues of the herbicide in water, food, urine and breast milk.

The EPA’s weed management plan will not address human health concerns, but the agency is also analyzing health data as part of a required reevaluation of the herbicide.

The EPA’s preliminary risk assessment of glyphosate is expected to be released for public comment later this year, and the agency will publish its proposed weed management plan for public comment at the same time.

Regulators in the United States and many other countries have long considered glyphosate among the safest herbicides in use. A review of the chemical by the German government for the European Union last year concluded that no link to cancer has been established.

And Monsanto Co., which held the patent on glyphosate until 2000 and last year sold more than $5 billion of Roundup herbicide, says the weed-killing agent has been proven safe repeatedly. Last week, the company blamed "agenda-driven groups" for fueling false reports about glyphosate.

But the chemical’s critics, including environmentalists, scientists and opponents of genetically modified foods, hope the WHO finding will help convince the EPA that tighter controls on the herbicide are needed, not just to prevent the growth of herbicide-resistant weeds, but also to protect human health.

Globally, the herbicide is a key ingredient in more than 700 products and is used to control weeds in gardens, along roadsides and on millions of acres of farmland.

At least 283.5 million pounds of glyphosate were used in U.S. agriculture in 2012, the most recent year for which data is available, up from 110 million pounds in 2002, according to the U.S. Geological Survey. (reut.rs/1NcACgm) According to the U.S. Department of Agriculture, more than 90 percent of the soybeans and cotton grown in the United States last year, and 89 percent of the corn, was genetically modified to withstand herbicide applications.

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