· Wireworm infestations are common in some areas of south-southwest and south-central Illinois.
· Explanation of wireworm biology and chronic wireworm problems.
· Request for information about fields with wireworm infestations.
We have written about wireworms in several previous issues of the Bulletin, so this article is simply a status report. Duane Frederking, with Pioneer Hi-Bred International, reported that wireworm problems are relatively numerous in his area of south-southwestern and mid-southern Illinois. The larvae have attacked planted seeds and underground portions of seedling stems. The result in some fields has been significantly reduced plant populations, and some fields require replanting, at least in spots.
Wireworm problems are often difficult to predict. If a grower plants corn into former grassland, a wireworm problem is almost assured. However, what about the farmer who experiences wireworm problems in corn planted after soybeans in a field with no history of wireworm problems and no grassy weed problems? Your guess is as good as ours. Wireworm biology is still mysterious to many of us, and we can't seem to predict their occurrence with great accuracy. Dr. Armon Keaster, University of Missouri, is the most renowned wireworm expert in the Corn Belt. He and Dr. Thomas Riley co-authored A Pictorial Field Key to Wireworms Attacking Corn in the Midwest, and they provided some insight about wireworm biology. "Wireworm injury to crops usually occurs either after grassland has been converted to cultivated land or in fields with chronic infestations that are left uncontrolled for several years." Maybe the latter situation explains some of the problems.
The adults of wireworms, called click beetles, deposit eggs in the soil of grassy areas or cultivated fields, and the larvae require from one to several years to develop into adults. Consequently, wireworms can be problematic in the same field for more than one year. However, as Keaster and Riley pointed out in their booklet: "Most damage occurs when large populations contain a high percentage of mature or almost mature larvae." If this is what you are encountering, then it is likely that wireworm larvae have been present in the field for some time.
Refer to last week's Bulletin (issue no. 8, May 14, 1999) for information about replanting and controlling wireworms. Also remember that when the soil warms up appreciably, wireworm larvae will move downward in the soil, and we won't find them again for the rest of the year.
One final note: We are interested in obtaining information about fields that have relatively severe infestations of wireworms, particularly if replanting is occurring. John Shaw, research scientist in the Center for Economic Entomology at the Illinois Natural History Survey, is seeking a field in which to conduct a wireworm insecticide efficacy trial. In the past, we have placed such trials in infested fields that required replanting. If you have any knowledge about such fields, please contact John at (217)244-5124 or at email@example.com. He'd like to hear from you.--Kevin Steffey