Source: Associated Press

CHAMPAIGN, Ill. -- When the weed killer Roundup was introduced in the 1970s, it proved it could kill nearly any plant while still being safer than many other herbicides, and it allowed farmers to give up harsher chemicals and reduce tilling that can contribute to erosion.

But 24 years later, a few sturdy species of weeds resistant to Roundup have evolved, forcing farmers to return to some of the less environmentally safe practices they abandoned decades ago.

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But with any herbicide, the more it's used, the more likely it'll run into individual plants within a species that have just enough genetic variation to survive what kills most of their relatives. With each generation, the survivors represent a larger percentage of the species.

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That said, the company has started paying cotton farmers $12 an acre to cover the cost of other herbicides to use alongside Roundup to boost its effectiveness.

The trend has confirmed some food safety groups' belief that biotechnology won't reduce the use of chemicals in the long run.

"That's being reversed," said Bill Freese, a chemist with the Washington, D.C.-based Center For Food Safety, which promotes organic agriculture. "They're going to dramatically increase use of those chemicals, and that's bad news."

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