Entomologists across the Corn Belt recorded a significant increasing European corn borer (ECB) populations from 2000 to 2001, with second-generation borers being especially numerous.
What 2002 will bring is any entomologist's guess, though history would indicate a year of high ECB populations is on the horizon.
"European corn borer is a very unpredictable insect," says Kevin Steffey, Extension entomologist, at the University of Illinois. "In 2001, we saw a significant increase in second-generation ECB throughout some areas of the state, particularly northern Illinois. Apparently environmental, factors, such as the weather, the relative lack of natural control measures and the quality of the corn crop, came together to enhance mating and egg laying."
In Minnesota, results of the annual Department of Agriculture fall survey show a marked increase in the over-wintering number of both biotypes of ECB common to the area--univoltine and second-generation bivoltine. University of Minnesota Entomologist Ken Ostlie reports that number appear to be growing since the peak years of 1995 and 1996, and researchers there are waiting to see if the high adoption rate of Bt corn among the state's growers has any impact on the cyclical nature of the insects. The state has seen an unprecedented number of low-infestation years.
Typically, ECB populations fluctuate in a cycle that may range from four to seven years. Populations peak and subsequently take a significant drop. This cyclical pattern has been observed and documented by entomologists since the 1940s. In fact, Steffey reports that data documenting these observations will be posted on the University of Illinois' web site this spring.
Researchers, at Pioneer Hi-Bred International Inc., have been tracking harvesttime ECB infestation levels on a national basis since 1997. Their observations also reflect an increase in infestation levels, in 2001, particularly in Illinois, Iowa, Nebraska, eastern areas of the Dakotas and in southern Minnesota.
A map of 2001 infestation levels, on a county-by-county basis, indicates corn borer pressure was not only widespread, but the populations levels were much higher, many 70% or more, in most of the counties in 2001 vs. 2001. The same map from 2000 shows ECB pressure over much of the same geography, but the majority of the infestation levels were at 30% or below.
In 1998 and 1999, populations were very low, but the number have increased in 2000 and 2001, indicating a possible upswing in the ECB cycle. A similar cycle began with high number in 1990 and 1991, and then low levels building to highs in 1995 through 19976, depending on geography.
"1997 was our last year of high corn borer populations in Illinois and across the Corn Belt," Steffey explains. "Odds are really good, in 2002, numbers of at least first generation ECB will be higher than 2001, primarily because numbers were high going into the winter."
Winter weather likely as to be extremely cold or warm to have any significant impact on overwintering corn borers. The most important factors that affect ECB in the spring are spring weather conditions and the presence or absence of parasitoids and pathogens.
Ostlie also reports that the current length of the span between corn borer peaks in Minnesota is unprecedented.
As human nature kicks in and growers seek a simple answer to the question of what to do to avoid losses from ECB in 2002, the guessing game begins again.
"There is no simple answer," echo the experts.
Growers can take their chances and do nothing. They can plan to scout fields and be prepared to treat if borers reach economic levels, or they can plant ECB-resistant hybrids. The experts recommend using ECB-resistant hybrids to manage the risk of potential yield losses.
"Growers know their level of risk," says Mutt McLeod, entomologist an agronomy research manager for Pioneer, in Windfall, IN. "They also know their fields and which ones will be planted early and those that are more prone to corn borer infestation. I typically recommend growers use resistant hybrids on a portion of their acres, particularly on the high-yielding acres."
For example, McLeod explains that an 8% yield benefit where the yield potential is 200 bushels-per-acre delivers a greater overall return than that same 8% on a 130-bushel-per-acre field.
"Every grower has a different need for risk management and using ECB-resistant hybrids is like purchasing an insurance policy," Ostlie says. "Every bushel is important, but some growers can tolerate less fluctuation in yield and need to invest more in insurance. I definitely think now is a good time for growers to evaluate their corn borer risk management."