More US weeds found resisting Monsanto Roundup

KANSAS CITY, Mo., Feb 26 (Reuters) - Scientists said on Friday they have confirmed expanding weed resistance to a key ingredient in Monsantos (MON.N)widely used Roundup herbicide, a troubling development for farmers and fresh fodder for Monsanto critics.

Kansas State University said scientists had found five kochia weed populations in western Kansas that have been confirmed to have become resistant to glyphosate.

Kochia, also called fireweed, is a drought-tolerant weed commonly found on land in the western United States and Canada where crops are grown and cattle are grazed.

"This complicates and may increase control costs for those growers who may have a resistance problem, but there are other herbicides," said Kansas State weed scientist Phil Stahlman.

Stahlman and other university researchers are recommending farmers use other herbicides to try to control the weeds.

Monsanto said it was working with university scientists on a multi-state effort to keep evaluating the problem and advise farmers how to respond.

The company declined to answer questions about how significant the resistance problems are to date, and if resistance is expected to expand further.

Weed resistance to glyphosate, a key ingredient in Roundup herbicide, has been mounting across the United States in recent years as Monsantos genetically modified "Roundup Ready" corn, soybeans and other crops have gained popularity with farmers.

Monsanto has genetically altered the crops so they can withstand dousings of Roundup herbicide. But environmentalists and other critics claim herbicide usage has increased, making weeds more resistant, which ultimately makes it more difficult to kill weeds and leads farmers to boost use of other types of herbicide as well.

It is common for weeds to develop resistance to herbicides. So far, more than 130 types of weeds have developed levels of herbicide resistance in more than 40 U.S. states, more resistant weeds than found in any other country, according to weed scientists.

Experts estimate glyphosate-resistant weeds have infested close to 11 million acres.

"All being driven by Roundup Ready crop systems," said Bill Freese, science policy analyst for the Center for Food Safety.

Freese said the U.S. government needs to do a better job of regulating herbicide-tolerant crops and herbicide usage.

"Weve been telling USDA for several years now that they have to regulate the herbicide-tolerant crop systems that are driving the evolution and spread of these noxious weeds," Freese said.