U.S. Corn Borer Populations Reduced

DES MOINES - Dec 20/04 - SNS -- European corn borer (ECB) numbers and the damage caused were down across the U.S. Corn Belt this year and the outlook is for further reductions in 2005 because of low overwintering populations.

"It is very difficult to accurately predict if an insect such as ECB will reach its reproductive potential," says John Obermeyer, Extension entomologist at Purdue University. "More than any other factor, environmental conditions during the growing season will determine whether this insect becomes a serious threat in 2005."

Obermeyer explains that wet spring weather, similar to what the Corn Belt experienced in 2004, has an adverse effect on the mating and egg-laying of ECB -- which results in low overwintering populations.

However, with prime environmental conditions for egg hatch, growers could still see heavy second-generation ECB infestation levels. Under optimal conditions, each female corn borer can lay 400 eggs across many locations, quickly populating a previously non-populated area.

Although overwintering numbers are at a 5-year low, Obermeyer encourages producers to calculate the economic risks before making a decision not to plant a Bt hybrid.

"We've been studying the economic impact of this pest for years," says Obermeyer. "Even with the low amount of ECB damage in 2004, the state average remains at a $5 to $6 loss per acre. The investment in insect-resistant hybrids is about or a little less than that."

Kevin Steffey, Extension entomologist at the University of Illinois, agrees that first-generation ECB pressure probably won't be high, but the second generation is unpredictable.

"The fact is that densities could explode," says Steffey. "Insects are notorious for that -- going from one to thousands in just two generations."

Illinois also experienced extremely low ECB pressure throughout the growing season in 2004. The University of Illinois' annual ECB survey reports the average% infestation of second-generation ECB per 1 00 plants was only 17.1%. However, Steffey cautions growers to examine long-term ECB trends in the area where they'll be planting.

"Our fall survey does no more than give a snapshot of ECB pressure from the past season and where we'll start the next growing season," says Steffey. "Planting dates, weather patterns, storms , extreme weather (wet or dry), natural enemies - all effect ECB pressure. Depending upon the combination of these factors, ECB populations can go either up or down, whether they get off to a relatively slow start or not."

Murt McLeod, entomologist and agronomy research manager for Pioneer Hi-Bred International, Inc., also cautions growers not to use overwintering populations as the only factor in determining whether to use a Bt technology for the next year.

"Too many environmental factors influence ECB pressure to base decisions strictly on overwintering populations," says McLeod. "We've had a couple of years of low pressure. But be very careful in using that as an indication of what's to come in 2005. Corn borer pressures are very hard to predict. Low ECB pressures in 2004 has absolutely nothing to do with 2005."