PEORIA. Illinois - Mike Schachtrup isn't taking any prisoners. "A dead weed can't be resistant," said the farmer who grows corn and soybeans - much of it the Roundup Ready variety - on about 5,000 acres with his brothers in Peoria, Tazewell, Knox and Warren counties.

Scientists at universities around the country have noted that weed resistance has been on the increase for the herbicide glyphosate, the chief ingredient in Roundup Ready products developed by St. Louis-based Monsanto Co.

Glyphosate surged to popularity in the mid-1990s after the development of genetically-engineered soybeans and other crops that are immune to the herbicide. That meant farmers could use Roundup weed killer and Roundup seed bean without fear of other weeds turning up.

Monsanto harvested a winner with that one. The firm said 87 percent of U.S. soybean fields and 60 percent of international soybean fields were planted with Roundup Ready soybeans in 2005.
 
But a growing number of weeds are now reportedly showing resistance. "It was just a matter of time," said Aaron Hager, a weed scientist with University of Illinois Extension. "We now have instances of weed species that aren't controlled by glyphosate," he said.

Hager said weed resistance stems from the plant kingdom's diversity and ability to adapt. "If only one waterhemp plant survives in a field (treated with glyphosate), that will be the only survivor to make seed. That seed will then generate hundreds of glyphosate-resistant plants," he said.

Schachtrup thinks weed resistance may result if farmers apply the herbicide when conditions aren't right. "You have to apply it when the plant can accept it. It should be 70 degrees and sunny," he said.

But it takes more than herbicides to keep a good weed down, said Bob Hartzler, an agronomy professor at Iowa State University. "Glyphosate is a remarkable chemical. There's nothing else like it. It's a once-in-a-lifetime herbicide," he said.

Yet every lifetime must come to an end, noted Hartzler. "There's good evidence that the more you use it, the more likely the resistance," he said.

The threat of weed resistance isn't sending Monsanto into a tailspin. "We don't have a lot of concern about it. All herbicides experience resistance," said spokeswoman Geri Berdak.

Monsanto offers a Web-based program to help farmers deal with weed resistance issues, she said.

With a huge corn crop expected this year, Monsanto looks for Roundup Ready corn to be planted on 40 million acres in the 2007 season, compared with 32 million acres in 2006.

Steve Tarter can be reached at 686-3260 or _starter@pjstar.com.
© 2007 PEORIA JOURNAL STAR, INC.

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