COLUMBIA, Mo. -- Farmers harvesting corn this fall should review seed contracts signed last spring, said Bill Wiebold, University of Missouri extension agronomist.

"It will be important to remember agreements to keep special hybrids, such as those selected to tolerate glyphosate herbicides, separated from regular marketing channels," Wiebold said.

The glyphosate-tolerant hybrids, mostly know as Roundup Ready, produce grain not approved for import into most European countries. Most seed companies ask producers at the time of purchase to sign a contract to follow approved marketing channels. In the contracts buyers assume much of the responsibility for proper marketing.

"It is illegal to sell grain to unapproved markets, even if the marketing is unintentional," Wiebold said. "Small amounts of unapproved grain can contaminate a shipload of grain. This contaminated grain can be turned back at the market."

"That's why it is important for producers to check their contractual obligations," Wiebold said.

Seed companies that released varieties not approved for all markets attempt to control the flow of grain into approved channels, Wiebold said. "This is the source of a new term we are hearing in marketing: channeling."

Complicating the job of tracking and identifying grain from unapproved varieties is the cross-pollination in crops such as corn. Pollen from the new varieties carry genes that can produce unapproved grain in other fields of approved varieties. That can happen, with the drift of pollen, at a great distance.

"It is important that producers do what it takes to ensure the integrity of the U.S. corn supply and our relationships with foreign buyers," Wiebold said. "Failure to do so will put this specific technology in jeopardy."