Conventional corn beckons old foe

Is a corn borer comeback in the cards?

Outside expanding fields of conventional corn, an old yield robber is waiting in the weeds and likely planning a return. Corn borer appeared to meet its Waterloo in 1997, when

Bt corn made a smash-hit debut and began wiping fields of the pest. However, nature is a patient player. With a consistent increase in conventional acreage plantings, corn borer might be waking from 20 years of slumber.

As the marketplace became saturated with Bt corn it lowered the carrying capacity for the larvae. Yet, severely diminished is a far cry from extinct. Dorian Gatchell, a boots-on-the-ground agronomist with Minnesota Agricultural Services, walks the rows of southwest Minnesota's rich prairie soil. He finds a few corn borers every year, but he doesn't see numbers anywhere close to a problem yet.

"Is the conventional corn increase going to boost corn borer? I think it will in time," he says.

Gatchell looks for corn borer when corn reaches V6. First-generation moths are attracted to the tallest corn in an area. The larvae eat straight through the whirl, and telltale holes are exposed as the leaves unfurl. The holes are highways for vascular disruption, disease and stalk breakage. If a producer goes to sleep on corn borer, it will be the first and only time. The yield losses drive home a hard lesson.

This year, Gatchell has customers with corn borer concerns and in response he's setting up pheromone traps for moths. "Corn borer isn't complicated, but we must be vigilant and that means monitoring moth flights and eyeballing fields to scout for damage," he says.

Corn borer egg-larvae-moth life cycles can occur multiple times per year, depending on geography. Traps with a pheromone vile in the center attract adult moths, which helps determine the best time to scout.

Bruce Potter, Extension integrated pest management specialist at the University of Minnesota Southwest Research and Outreach Center, says severe infestations can wipe out yield. "Pay attention, scout properly and it can be dealt with. There are far more options for corn borer than rootworm," he says.

The University of Minnesota has black light traps across the state to trap corn borers and other insects to help determine the best time to scout. Potter also expects corn borer to gain steam.

"Bt hammered borer and everyone got the benefits, even organic growers," Potter says. "But corn borer isn't dead by any stretch and with several years of conventional, I'd expect populations to rebound."

Arlen Koepp, a Clarkfield, Minn., farmer, has almost abandoned traited acreage—95% of his corn is in conventional plantings. In 1996, just before Bt introduction, his fields were hit hard by corn borers, bringing major lodging and yield loss. "I'm going with traps this year and will spray if they're present above the economic threshold. Borer will be back at some point and I've got to be ready," he explains.

Koepp's conventional return was dictated by dollars. "I might run into borer problems with this much conventional acreage, but GMO corn priced me out. This is strictly an economic decision. I want to use Bt corn, but it isn't priced competitively."

With lower commodity prices, interest in moving to less traited and conventional hybrids has grown. In a sense, farmers planting non-Bt hybrids get the best of both worlds: lower seed prices and proxy Bt protection from the vast domain of traited acreage. However, every conventional acre increase opens the window of opportunity a bit wider for corn borer's return.