Monsanto shares fall as South Korea joins pause in wheat imports

Investors drove down the price of Monsanto shares by 4 percent on Friday as South Korea joined Japan in suspending imports of U.S. wheat after an unapproved strain of genetically modified wheat was discovered in a field in eastern Oregon.

The strain of wheat, designed to resist harmful effects from Monsanto’s Roundup weedkiller, was never commercially developed by the St. Louis-based agriculture giant in large part because wheat growers did not want to risk retaliation from their biggest export markets.

Fields used to test new crop varieties are burned and checked for surviving crops. So the mysterious appearance of the Monsanto wheat has raised questions about how the strain traveled there and whether it is lurking in the commercial wheat crop.

As a precaution, South Korea, which last year bought about half of its wheat imports from the United States, said it would halt purchases while it runs tests this weekend on wheat and flour that it has already imported. The European Union is also testing supplies.