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Preliminary Root-Rating Results for Urbana Corn Rootworm Trial

July 27, 2001
On July 16, a crew led by John Shaw, Illinois Natural History Survey, dug and washed roots from an experimental corn rootworm trial located just south of Champaign-Urbana. The following day, we rated the roots for larval injury, and we now present some of the preliminary results in Table 1.

Several of the following granular soil insecticides provided excellent-to-good protection despite the very significant corn rootworm larval injury in the control treatment (root rating = 5.5, 2-1/2 nodes of roots destroyed): Counter CR, Aztec 2.1G, Nufos, Force 3G, and Fortress 5G. In general, Capture 2EC and Lorsban 15G provided less consistent protection than the aforementioned products. Regent 4SC (50%) and Furadan 4F (15%), along with the seed treatments ProShield (53%) and Prescribe (20%), provided the least consistent levels of root protection (percentage of roots with injury ratings less than 4.0).

The preliminary results from this experiment indicate that several products that are marketed to protect corn roots from corn rootworm larvae do not offer consistent levels of protection. This is especially true for Regent 4SC, ProShield, Prescribe, and Furadan 4F. At best, the odds of witnessing heavy root pruning (root rating 4.0 or greater) with these products in our experiment were similar to guessing correctly "heads or tails" when flipping a coin. The odds of a correct choice were even more dismal for Prescribe and Furadan 4F.

Unfortunately, most producers do not monitor their corn or soybean fields (east-central Illinois) for corn rootworm adults; therefore, they do not have much of an indication regarding what the level of rootworm injury will be the following season. For this reason, most producers elect to use a soil insecticide as corn rootworm "insurance." We provide these results so that producers can make more informed choices the next time they pore through the blitz of product promotion literature.

We intend to share the results from our DeKalb and Monmouth insecticide efficacy trials during the next several weeks as these data become available.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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