Like most growers using a corn-soybean rotation, Jim Wilkinson never used to sweat corn rootworm problems in first-year corn.

But that has changed. Female western corn rootworm beetles have started laying eggs in soybeans in his area.

Wilkinson's one of an increasing number of growers in a pocket of eastern Illinois and western Indiana who have lost yield to rootworm damage on first-year corn.

While some are considering longer rotations to combat the problem, most are sticking with two-year rotations and are applying rootworm insecticide on all their first-year corn.

Growers in the two states have reported occasional rootworm feeding in first-year corn for several years. But the number of reports shot up in 1993, and has continued to increase.

University of Illinois and Purdue University entomologists say the problem currently is confined to nine counties in Illinois and 16 in Indiana.

"The area affected is expanding, but we don't know the rate," says Larry Bledsoe, a Purdue entomologist. "That is what some of the current research in both states is addressing."

Wilkinson farms in the middle of the affected area.

"I can't remember the last time I used rootworm insecticide until I finally identified this problem in 1993," he recalls. "Now I feel it's necessary.

"As a proponent of scouting and integrated pest management, I'd like to be able to predict when and where I should use insecticides," he adds. "But this is one case where we don't have enough information to predict which fields will need this insecticide. So we'd rather spend the money and protect the crop than risk losing it."

Jay Carlson, Wellington, IL, can not remember when he last used a corn rootworm insecticide, either - before 1996, that is. About pollination time in 1994, he had a 100-acre field hit by heavy rain and wind and half the corn went down.

"When we inspected the field, you could easily pull up any stalk with just one hand," he says.

Carlson was not sure why his first-year corn after soybeans got hit in '94. Seed company agronomists and others told him it was probably just a fluke, so he didn't use a rootworm insecticide in '95.

Big mistake.

"It turned dry, and root feeding was severe in much of our first-year corn," Carlson laments. "There wasn't enough moisture to keep the roots regrowing, and we lost quite a bit of yield."

Carlson gave in and put insecticide on all his corn in 1996 and again last year, at a cost of roughly $15 an acre.

"A University of Illinois study suggests it really didn't pay to use it in 1996, but at planting time, when I was looking back on 1995, I felt I couldn't take the chance of not having control."

Even on the fringe of the affected area in Indiana, John Remster, Valparaiso, says he's seen so much damage on first-year corn that he doesn't dare do without a planting-time insecticide.

Purdue's Bledsoe, along with University of Illinois entomologists Kevin Steffey and Mike Gray, plus Eli Levine and Joe Spencer, Illinois Natural History Survey entomologists, are working on the problem. The work includes intensive western corn rootworm monitoring and field observation.

Gray spent much of last summer digging in cornfields where beetle populations were monitored in soybeans in 1996. He hopes that enough quality data can be collected to come up with an economic population threshold for farmers within the affected area.

"We hope to learn the mechanism behind the changed egg-laying behavior and provide growers with guidelines to determine at which level rootworm population densities in soybeans will lead to problems in first-year corn," Levine says.

However, at this point Steffey cautions against adopting any specific number of beetles in beans as an economic threshold for using an insecticide in the following corn crop.

"Such a threshold is probably not based on any reliable data," he states.

Steffey also discourages the indiscriminate use of corn rootworm insecticide in first-year corn.

"Integrated pest management includes judicious use of insecticides, and we must be judicious in this practice, even within the affected area."

Growers who noted corn rootworm feeding in first-year corn for the first time last year are encouraged to contact their local extension offices.