A new variant of the northern corn rootworm with eggs that lay dormant for a year is spreading. The danger is that first-year corn is vulnerable in fields that normally would be protected by regular rotation practices.

The “extended diapause variant” was previously only observed in parts of northwest Iowa, southwest Minnesota, northeast Nebraska and southeast South Dakota. It has now been found in southwestern Iowa, not far from the Missouri state border, Monsanto reports.

The species has adapted to a corn-soybean rotation by delaying its egg development. It lays its eggs in cornfields, but the eggs take two years to hatch – after the fields have been rotated from corn to soybeans and back to corn.

“We did some root digs and discovered a lot of feeding on the roots of first-year corn that didn’t have rootworm protection,” Bruce Ketchem, a grower in Shenandoah, Iowa, about 10 miles from the Missouri border, said in a Monsanto release.

After talking with local agronomists, Ketchem says they confirmed the northern diapause variant was the culprit. There’s not much he can do about it this year, but experts agree the key to preventing problems next year is scouting for rootworms this season.

“The best thing for farmers to do to find out if they have a risk is to go out and dig roots in their first-year corn fields right now and see if they have rootworm pressure,” says Dave Rhylander, Director of Traits at Monsanto. “Alternatively, they could use yellow sticky traps to see if they have rootworm beetles.”

If growers discover they have a problem, entomologists recommend they use some form of rootworm protection next year, whether it’s a soil insecticide, a seed treatment or in-plant protection, such as YieldGard Rootworm or YieldGard Plus, which combines the protection of YieldGard Rootworm Corn and YieldGard Corn Borer in one seed.

Monsanto says it is the first corn technology to deliver whole-season, in-plant protection against European and southwestern corn borers and effective and consistent protection against western and northern corn rootworms.