Issue No. 24, Article 3/November 3, 2006
Results from the 2006 Fall Survey for Second-Generation European Corn Borers
We finally found an opportunity to compile and analyze the data gathered during our annual fall survey of second-generation European corn borer populations. A summary of the data is presented in Table 1. At a near-future date, a complete PowerPoint slide set will be uploaded to the IPM Web site. This link directs you to the European corn borer Web page. Look for Fall Survey 2006 under "Related Links" and click. A fact sheet that describes the history and procedures used for the annual European corn borer survey also can be found on the European corn borer Web page.
Population densities (number of borers per 100 plants) increased noticeably in most counties and most crop reporting districts from 2005 to 2006. Relatively large densities of second-generation European corn borers were evident in the West and West Southwest crop reporting districts (73.77 and 76.88 corn borers per 100 plants, respectively). The mean percentages of corn plants infested with European corn borer larvae in these same two crop reporting districts were 39% and 46%, respectively. Five counties had average densities of more than 100 larvae per 100 plants--Adams (131.8, the largest county density in 2006), Warren (113.4), Greene (104), Montgomery (105), and Morgan (124). The statewide average number of larvae per 100 plants was 23.24, and the statewide level of infestation was 33%. Very few European corn borer larvae were present in cornstalks in many southern counties (Southwest and Southeast crop reporting districts). In fact, none were found in four of the eight fields sampled in those districts. However, several fields were infested with southwestern corn borer larvae, although those data are not reported here.
Interestingly, the statewide average number of second-generation European corn borers per 100 plants in Illinois was lower in 2006 (23.24) than in 2005 (34.4). However, the average percentage of infestation of corn plants was 24.2 in 2005 and 33 in 2006. In many of the counties in western Illinois, cornfields had either no European corn borer infestations or were 80% to 100% infested. Of the 498 fields surveyed, 244 (49%) had 0% infestation, whereas 75 (15%) had between 76% and 100% infestation (27 of 498 fields, or 5.4%, had 100% infestation). It is important to point out that although 49% of the fields surveyed had no European corn borer infestation, this does not necessarily mean that all of these fields were planted with Bt corn for corn borer control. As indicated previously, some of the fields with no European corn borer larvae were infested with southwestern corn borer larvae. In addition, some non-Bt cornfields may have had very low-level infestations of European corn borers or no infestation at all.
As we have stated many times before, data from the annual survey of second-generation European corn borers usually cannot be used to predict infestations of European corn borers the following year. However, we certainly know that the larger the population in the fall, the greater the potential population for first-generation European corn borers the following spring. Obviously, weather and natural control agents will have a major impact on corn borer populations in 2007, but corn growers in western Illinois should be on alert nonetheless. Two disease organisms that infect European corn borer larvae, Beauveria bassiana (a fungus) and Nosema pyrausta (a microsporidian), were not readily apparent in most of the cornfields surveyed in 2006.
Entomologists in most states no longer conduct annual surveys of European corn borer larvae, and there is rationale for discontinuing the activity. However, because we have a mostly continuous set of annual data (except for two years) since the mid-1940s, we continue to build the Illinois data set. With results like we experienced in 2006, it seems that the time and effort spent collecting the data was well worth it.
We thank all of the Extension educators, county Extension personnel, graduate students, and academic professionals who helped us gather the data for the annual fall survey of European corn borers in 2006. Without their volunteer help, we would not be able to support a survey of such magnitude.
Look for the PowerPoint slide set in the near future. We'll place a notification in the Bulletin.--Kevin Steffey and Mike Gray