Corn Borers in Illinois: Past, Present, and Future
|
| Report |
The European corn borer, Ostrinia nubilalis (Hübner), was accidentally introduced into North America from Europe in the early 1900s, probably in shipments of broom corn from Hungary or Italy. It was discovered first in North America near Boston, Massachusetts, in 1917. By 1952, the European corn borer had spread throughout most of the major corn-growing areas in the United States. It first appeared in Illinois in 1939. After it became established in North America, the European corn borer was recognized as one of the most economically important insect pests of corn throughout the Corn Belt. For information about the biology and management of European corn borers, refer to our fact sheet at http://www.ipm.illinois.edu/fieldcrops/insects/european_corn_borer/factsheet.html.
History and Objectives of the Fall Survey For European Corn Borers
s the European corn borer spread throughout North America, scientists became interested in monitoring its spread and estimating densities. Consequently, entomologists in many north-central states initiated formal and systematic surveys of second-generation European corn borers. In 1941, entomologists at the University of Illinois and Illinois Natural History Survey conducted the first survey of second-generation European corn borers in 36 counties in Illinois. Fall surveys have been conducted in essentially the same way every year since 1942. We have annual data from these fall surveys from 1943 to the present, except for 1997 and 1998, years during which the survey was not conducted.
The objective of our fall surveys is to obtain estimates of densities of second-generation European corn borer larvae in crop-reporting districts in Illinois. Not all counties are sampled every year. The number of counties surveyed in Illinois each year has varied over time; however, 35 to 50 counties usually are surveyed within a given year. Although some counties have been surveyed virtually every year since 1943, other counties have been surveyed less frequently, and some counties have never been surveyed. Results from nearby counties can be used as reasonable estimates of corn borer densities in counties that have never been surveyed.
The estimates of second-generation European corn borer densities can be used to estimate the economic impact of corn borers during any given year. The economic impacts can be compared over time and among counties and districts within the state. In addition, population trends can be determined. Although densities of second-generation European corn borers in a given year suggest potential overwintering population densities, predictions of densities of corn borers for the following year are tenuous. Many factors (for example, weather and natural enemies) regulate European corn borer populations, so predicting populations from one year to the next is not an exact science. A review of average densities of second-generation European corn borers in Illinois from 1983 through 2002 (20 years) reveals the unpredictability of populations from year to year.
The Database and the Web Site
The data from fall surveys of second-generation European corn borers from 1943 to the present are available online. At the site, click on "European Corn Borer" in the left panel to load the database. From this page, you will be able to view data for individual counties, for crop-reporting districts, or for the state. For individual counties or specific crop-reporting districts, you can select thecounty or district of interest from the menus provided, or you can click on the county or district in the outline map. If you do the latter, the county or district of interest will be indicated in yellow.
Remember, not all counties have been surveyed, and some counties surveyed have not been surveyed every year. Counties that have never been surveyed are indicated in the pull-down menu with "no data" in parentheses. However, if you click on such a county, you can obtain data from four nearby counties.
You also can view data for all years or for selected years (for example, 1950 to 1975 or 1990 to 2000). In the lower portion of the panel, you can access specific information for a given year for either individual counties (default) or crop-reporting districts. The information is presented in both graph and colored-map formats. The manner in which the data are presented (class options—natural break, quantile, equal interval, standard deviation) can be changed, and the options are explained when you click on "Class Options" and then "Help." For a brief explanation about how to use and navigate the web pages, click on "Help" in the upper right of the panel entitled "European Corn Borers."
European Corn Borers in Illinois in 2002
Because corn was planted late in several areas of Illinois in 2002, the potential for infestation by first-generation European corn borers increased, as did the potential for second-generation corn borers. Our fall survey in 2002 revealed that the statewide average number of European corn borers per plant (0.95 borer per plant) was essentially the same as the statewide average number of borers per plant (0.91 borer per plant) in2001. However, some areas had heavier infestations than others. Densities of European corn borers were largest in a band from southwestern Illinois (Monroe County, 3.01 borers per plant) to central Illinois (McLean County, 1.43 borers per plant). Other counties with an average of more than one European corn borer per plant were Adams (1.19 borers per plant), Christian (1.03 borers per plant), Effingham (2.29 borers per plant), Logan (2.74 borers per plant), Madison (2.6 borers per plant), Morgan (1.41 borers per plant), and Washington (1.62 borers per plant). In general, the counties in eastern Illinois had very low densities of European corn borers.
The most dramatic decrease of average numbers of European corn borers per plant from 2001 to 2002 occurred in the northwest and northeast crop-reporting districts. The most dramatic increase in average numbers of corn borers per plant from 2001 to 2002 occurred in the west-southwest and southwest crop-reporting districts.
A review of the raw data strongly suggests that we should present the data from our surveys in additional ways. Most surveyors indicated that infestations of European corn borers were either absent or relatively heavy in many areas of the state. It is not unusual for data from a county to include a range of 0 to 100 percent infested plants with 0 to 3 borers per plant. Although we do not know what type of corn hybrid we are sampling during the survey, it is apparent that we are sampling both Bt cornfields and non-Bt cornfields. Consequently, the averages for a given county or crop-reporting district may not tell the whole story.
Managing European Corn Borers in 2002
Corn hybrids genetically transformed to resist European corn borer, southwestern corn borer, and a few other pest Lepidoptera were commercialized for the first time in 1996. Since 1997, the market for Bt corn has grown, ebbed, and then grown again, primarily responding to export concerns, densities of European corn borer, and media uproar. Regardless, Bt corn has become part of our agricultural landscape in North America and offers significant benefits when densities of European or southwestern corn borers reach economic levels.
Although several transgenic corn events for insect resistance have been commercialized, only one of them (Monsanto's event MON810; trade name YieldGard Corn Borer) was available through 2002. A new transgenic event for corn borer resistance, Herculex I Insect Protection, will be available in several corn hybrids for the first time in 2003.
Herculex I Insect Protection, developed by Dow AgroSciences and Pioneer Hi-Bred International, expresses the Cry1F insecticidal protein, a different protein from the one (Cry1Ab) expressed by YieldGard Corn Borer products. Herculex I hybrids control European and southwestern corn borers as well as YieldGard Corn Borer hybrids. Other pest Lepidoptera included on the Herculex I "label" include black cutworm, corn earworm (suppression), and fall armyworm.
Herculex I is fully approved in the U.S. for food and feed, and full approval was received in Japan in 2002. However, Herculex I currently is not approved for export to Europe. Herculex I will be available commercially in Mycogen Seeds hybrids for the 2003 growing season. The insect-resistance management requirements for Herculex I are identical to the insect-resistance management requirements for YieldGard Corn Borer—a minimum of 20 percent of acres for non-Bt corn refuge, planted within half a mile of fields with Bt corn hybrids.
For growers who are not interested in using Bt corn for management of European and southwestern corn borers, several insecticides are registered for their control. Diligent scouting and timing of insecticide application are keys to the successful control of these corn borers. Management worksheets enable growers to determine whether control is necessary based upon percentage infestation, potential impact on yield, yield expectations, value of the corn crop, and cost of control.
Pyrethroid and organophosphate insecticides dominate the list of available products for control of corn borers—*Ambush 2E, *Capture 2EC, *Lorsban 4E, Lorsban 15G, *Mustang, *Penncap-M, *Pounce 1.5G and 3.2EC, and *Warrior (*denotes use only by certified applicators). However, two other classes of insecticides—naturalytes and insect growth regulators—are represented by the products Tracer 4SC (the active ingredient is spinosad) and Intrepid (the active ingredient is methoxyfenozide). These products have been registered for use on corn only recently and have not been used widely in Illinois.