Hal Willson, Extension Entomology, OSU

At one time, rootworm injury to corn was primarily regarded as a continuous corn problem since egg laying of either the northern corn rootworm or the western was usually limited to corn fields from which the eggs hatched the following season and the larvae fed on root systems of the continuous corn. In the 80s, the extended diapause behavior causing injury to 1^st year corn by northern corn rootworm populations became recognized. In the 90s, the development of a new biotype of western corn rootworm resulted in egg laying in soybeans and injury to 1^st year corn.

During the past decade, the presence of first year corn injury in Ohio by both northern corn rootworm and western corn rootworm has been established. To facilitate risk prediction of first year corn rootworm problems, a cooperative effort to monitor adult rootworm activity in Ohio soybeans has been implemented by OSU Extension, independent consultants and agri-business personnel during the past three years.

The monitoring data presented in Table 1 predominantly represents collections of adult western corn rootworm (WCR) beetles on Pherocon AM yellow sticky traps in soybean fields adjacent to first year corn fields. The data represent the average number of WCR collected from four traps serviced on a biweekly schedule from mid-August to late September. An average catch of one to two WCR per trap per day would be regarded as relatively high catch in Ohio. County WCR collection averages approaching 0.5 indicate a potential for first year corn rootworm (FYCRW) problems at some sites within the area monitored. County WCR collection averages around 0.2 indicate a presence of FYCRW, but most of the sites monitored are expected to have minimal risk of a FYCRW problem.

In general, regions of FYCRW activity in Ohio are averaging ca. 0.2 WCR per trap per day. In counties bordering Indiana, average WCR activity in soybeans has declined over the past three years. WCR activity in counties in the 2^nd tier from the Indiana has been moderate with the exception of Putnam County. WCR activity in the 3^rd tier of counties has increased and indicates a dispersal of FYCRW activity. In central Ohio counties, WCR activity in soybeans remains very low indicating an absence of FYCRW activity.

Table 1. Trap Collections of Western Corn Rootworm in Ohio Soybeans, 1998 to 2000.