University of Illinois

No. 19/July 29, 1998

Field Observations: Preliminary Results from the Corn Rootworm Areawide Study

As we've mentioned several times in this Bulletin, we are investigating the feasibility of an areawide corn rootworm beetle suppression program located just south of Sheldon, Illinois. Last season, multiple applications of SLAM (MicroFlo Corp.) were applied to corn and soybean fields throughout the 16-square-mile experimental site. SLAM is an insecticidal bait that consists of cucurbitacins and a very low level of carbaryl (one ounce per acre). After a field has been treated with SLAM, beetles feed compulsively on the insecticidal bait (due to the presence of cucurbitacins), receive a lethal dose of carbaryl, and die before egg laying occurs.

Unlike the use of soil insecticides, areawide suppression programs are designed to lower the general equilibrium position of corn rootworm populations. What exactly does this mean? It is commonly observed within fields that receive a soil-insecticide application at planting that corn rootworm adults can still be quite numerous after emergence. Over time, corn rootworm populations can remain at economic levels year after year despite the use of soil insecticides. In essence, the pesticide treadmill can remain undeterred for many seasons. With an areawide suppression effort, the overall corn rootworm population theoretically canbe reduced if growers are willing to cooperate across a large area and collectively manage this insect pest.

In our areawide suppression research project, we have dug roots in 31 of 45 producers' fields. Preliminary indications suggest that fields within the core area (2 miles by 2 miles) have very little root injury. However, caution is urged in interpreting these preliminary results. Remember, we also had very low levels of root injury in our experimental root evaluations in DeKalb, Urbana, and Monmouth this year. We've speculated that the extremely wet June probably contributed to significant larval mortality. Root-rating results from Purdue University insecticide trials also suggest very low levels of larval pressure this season. However, some control (untreated) fields just outside the boundary of our 16-square-mile site had impressive levels of root lodging. We'll keep you posted on how the final results of this year's root digs look with respect to this novel pest management approach. In addition, similar trials are under way in Iowa, Kansas, South Dakota, and Texas. When the results from all states are analyzed we'll offer a comprehensive report.

Note: While digging roots in producers' fields in our areawide study in Iroquois County, we noticed the presence of corn leaf aphids and plentiful Japanese beetles. Silk clipping by Japanese beetles in some fields was impressive. Although many cornfields in the state are beyond the silking and pollination period, quite a few of the fields in the areawide study were shedding pollen. Stay tuned for more updates on this research project.

Mike Gray ( and Kevin Steffey (, Extension Entomology, (217)333-6652