And in Hawaii, organic papaya farmers are outraged because traces of genetically engineered papaya are showing up in their harvest.

Biologists call it "gene flow." It's how plants have swapped genetic material through cross-pollination since life first appeared.

But for people who choose to grow crops without genetically altering them, this natural biological exchange is a threat when bioengineered organisms are involved.

This week, already heightened tensions between the biotech industry and its foes peaked when the U.S. government published a study showing that genetically engineered grass found its way into conventionally grown grass some 12 miles away in Oregon's Willamette Valley.

The study led to renewed calls for tighter gene flow regulations, especially from farmers who promise customers that their products are free of genetically modified material.

More farmers are reporting finding trace amounts of genetically modified organisms cross-pollinated or otherwise mingled with their organically grown crops.

Those are potentially devastating discoveries because organic consumers generally demand that the higher-priced food they buy be free of biotechnological adulteration.

The problem, like the weather, respects no boundaries.

A NAFTA watchdog group said in March it had found genetically engineered corn in Mexico despite that country's 6-year-old biotechnology ban.

Meanwhile, consumers in Japan, Europe and elsewhere demand all their crops are grown conventionally. Farmers who can't make those biotech guarantees risk losing those markets.

U.S. labeling rules allow for trace amounts of genetically engineered material in organic products. Still, organic growers and other growers fear market perception will turn against them if customers perceive that gene flow isn't being controlled.

An increasing number of scientific studies show evidence that genetically engineered crops are creeping into conventionally grown fields, including the grass study conducted by the Environmental Protection Agency.

The Union of Concerned Scientists in February found trace amounts of genetically engineered seeds of corn, soy and canola mixed in with seeds that were supposed to be conventionally bred.

"We are concerned about gene flow," said U.S. Agriculture Department spokeswoman Meghan Thomas. But she said the USDA's regulatory reach extends only to experimental crops.

Once biotech crops are approved for market, as papayas were in 1997, the government's oversight essentially ends.

The levels of cross-pollination in other studies were found to be minuscule and industry leaders say gene flow concern is overblown.

"Organic acreage has really boomed at the same time biotech acreage has boomed," said Chris Horner, a spokesman for Monsanto Co. "With good agricultural practices there is no reason these two technologies can't coexist."