Those yellow-leafed soybeans that may soon dot your fields might not be a sign of nutrient deficiency or disease. Actually, they may be sending you a signal.

That signal is in the form of a marker to identify fields of Roundup Ready soybeans, says Randy Raque, district sales manager for Garst Seeds and a plant pathologist.

Raque is proposing to blend 1-2% yellow-leafed bean seed into Roundup Ready seed so fields are readily recognized as Roundup Ready. It will eliminate the accidental spraying of Roundup Ultra herbicide on non-Roundup Ready beans.

The markers will give custom applicators and growers a built-in safety factor, according to Raque. Even if a mix-up occurs and an applicator goes to the wrong field, he'll know right away there's been a mistake.

"Currently there are no systems in place to identify Roundup-resistant fields from non-Roundup-resistant fields," explains Raque. "This could virtually put an end to misapplications."

Raque is also working on a yellow-leafed variety with black seeds. Their benefit: If a grower planting Roundup Ready soybeans notices there are no black s oybeans, he'll realize it's the wrong seed.

Raque hopes seed companies will pick up on his idea and that by 2000 every bag of Roundup Ready beans sold will have this marker seed. He plans to develop a similar marking system for Liberty Link soybeans, using variegated-leaf beans as markers.

Technically, yellow-leafed soybeans have been around a long time, but haven't been used much.

"The reason most plant breeders do away with them is that they're chlorophyll-deficient and don't yield as well as regular soybeans," explains Raque. "From a yield standpoint, that's not what they're looking for."

Keith Whigham, an Iowa State University extension agronomist, says, "There's a different makeup that doesn't allow leaves (on yellow-leafed beans) to turn green like most soybeans. Therefore, they could work as markers."

When fields are sprayed, the yellow-leafed beans will be killed since they don't have the Roundup Ready gene. But Raque does not see that as a yield problem.

"It's not going to affect yields," Raque says. "You can knock out probably three, four or more percent. What I'm looking at here is probably 1-2%. You could take that much out of a field without affecting yield."

Raque developed the idea when he took a break from his seed-business career and sold commercial insurance to agribusinesses - including liability insurance for crop applicators.

"It was a very big concern for the insurance companies," Raque remembers. "We're not talking about just slight damage to a field where you're just making some adjustments. We're talking about total kill if you get in the wrong field."

While Raque calls the number of fields lost to misapplication each year "significant," Whigham doesn't quite see it that way.

"There has not been as much misapplication of Roundup as we anticipated when Roundup Ready soybeans were released," he says. "The cooperatives and farmers have done a better job of labeling the fields than I ever imagined they would. We hear of a few cases every once in a while, but it only takes one for that producer and/or the spray operator to learn."