European corn borer (ECB) numbers, as well as damage attributed to the insect, were at record lows across the U.S. Corn Belt in 2004. Given the resulting low overwintering populations, early-season threats from this pest are predicted to be relatively light. However, experts encourage growers to prepare for potential pressure from second-generation corn borer in 2005.
Planting insect-resistant hybrids with Bt technology, such as Herculex1 I insect protection, is an effective risk management tool against first- and second-generation ECB pressure. Entomologists agree investing in Bt technology can prevent yield loss, as well as limit the need for scouting and potential insecticide treatments throughout the growing season.
"Itâ€™s very difficult to accurately predict if European Corn Borer will reach its reproductive potential," says Marlin Rice, Iowa State University entomologist. More than any other factor, environmental conditions during the growing season will determine whether this insect becomes a serious threat in 2005.
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.
Entomologists caution corn growers
Although overwintering numbers are at a five-year low, farmers should calculate the economic risks before making a decision not to plant a Bt hybrid.
"Weâ€™ve been studying the economic impact of this pest for years," says Purdue University entomologist John Obermeyer. "Even with the low amount of ECB damage in 2004, the state average in Indiana 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 wonâ€™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 Illinoisâ€™ annual ECB survey reports the average percent infestation of second-generation ECB per 100 plants was only 17.1%. However, Steffey cautions growers to examine long-term ECB trends in the area where theyâ€™ll be planting.
"Our fall survey does no more than give a snapshot of ECB pressure from the past season and where weâ€™ll start the next growing season," says Steffey. "Planting dates, weather patterns, storms, extreme weather (wet or dry), natural enemies â€“ 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, an entomologist and agronomy research manager for Pioneer Hi-Bred 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. "Weâ€™ve had a couple of years of low pressure. But be very careful in using that as an indication of whatâ€™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."
Options for managing insect risks
Pioneer brand corn hybrids offer farmers several choices of Bt technology for the upcoming planting season, says McLeod. Hybrids containing the Herculex I insect protection offer the industryâ€™s broadest spectrum of in-plant insect control. The Herculex I trait provides excellent control of European (first and second brood) and southwestern corn borer, as well as fall armyworm. It also offers moderate resistance to corn earworm and is the only Bt gene offering in-plant resistance to black cutworm and western bean cutworm.
Pioneer also offers hybrids containing the YieldGard2 Corn Borer gene for season-long resistance to European and southwestern corn borer, along with intermediate resistance to corn earworm and above-average resistance to fall armyworm, notes McLeod.