The turf battles over herbicide-resistant crops have raged from the cornfield to the courtroom. But the first of these new-age weapons, IMI (imidazolinone)-resistant corn, continues to enlist more recruits and occupy more real estate.

The IMI-resistant gene was developed by American Cyanamid, initially with resistance to Pursuit herbicide. Garst Seed Co. (then ICI/Garst) and Pioneer put the first IMI-resistant hybrids on the market in 1991. In the next few years, most major seed companies added IMI resistance to their hybrid lineups.

IMI corn got a boost in 1997, when American Cyanamid released Lightning herbicide for one-pass, over-the-top weed control. Lightning blends the active ingredients of Pursuit (imazethapyr) and Arsenal (imazapyr) to control a wide spectrum of grass and broadleaf weeds. This spring, growers planted upwards of 3 million acres of IMI corn.

"Our IMI corn volume is going up every year," says David Weatherspoon, Garst's director of marketing. "IMI is our leading herbicide-resistant trait. The addition of Lightning herbicide has helped the demand for IMI-resistant hybrids."

"Asgrow is introducing IMI resistance into more elite hybrids every year," agrees Mike Wojtalewicz, the company's corn product manager.

"From 1997 to 1998, IMI corn acres nearly doubled," says Barney Bernstein, Lightning product manager for Cyanamid. "We put a lot of educational effort into making sure growers know how to use this system. Three times as much Lightning was used this year as in 1997."

While Lightning was cleared for field use in 1997, many corn growers used it for the first time this season. John Wescoat, New Madrid, MO, planted Pioneer 3395IR on March 28.

"I didn't put down preplant herbicide," says Wescoat. "Wet weather kept me out of the field until the corn was 18" tall. I had a lot of grass and morningglory in the field at that time, and sprayed Lightning over the top. It wiped out the weeds, but it took awhile.

"Because the corn was so tall, I cultivated some of it after I sprayed Lightning," he adds. "In hindsight, I probably shouldn't have. But Lightning did a good job. In fact, I wish I could have gotten it on more corn acres. I wound up having to fly on Accent and atrazine on some big corn to get rid of johnsongrass."

Lightning isn't cheap.

"But it's not as costly as the way I was controlling weeds before, with a preplant herbicide, followed by cultivation then an over-the-top spray," says Wescoat. "That gets expensive."

Corn growers have more weed-control options now - in the same hybrid.

"We are stacking more genetic traits all the time," says Michael Smidt, Garst's marketing communications manager. "We're still expanding IMI hybrids, and also are incorporating other genes, such as Liberty Link. For example, our 8585 hybrid now has IMI resistance, Liberty Link, Bt corn borer resistance and gray leaf spot resistance all stacked together."

That gives farmers more management choices in a single hybrid, but it can complicate score-keeping.

"When we stack genetic traits, it's harder to pinpoint the share of any one characteristic," agrees Smidt. "If a farmer buys a hybrid that incorporates both IMI resistance and Liberty Link, which most influenced his decision to go with that particular hybrid?"