University of Illinois

No. 25/December 5, 1997

Regent 80WG: A Wise Insecticide Choice for Corn Rootworm Protection?

On November 14, 1997, Regent 80WG was approved by the EPA for use in field corn. This insecticide will be a restricted-use product due to its toxicity to estuarine invertebrates and birds. We have received many questions from producers and dealers about its efficacy against corn rootworms. Many questions have been from producers in east-central Illinois who have been affected by western corn rootworm injury in first-year corn. In many instances, growers are looking for alternatives to granular soil insecticides applied conventionally through insecticide boxes on planters. How does Regent 80WG stack up when it comes to corn rootworm protection?

In 1996 and 1997, Regent 80WG did not perform well against corn rootworms in University of Illinois experimental trials at DeKalb, Monmouth, and Urbana (Table 1). Although many insecticides had less than optimal performances last season, the lack of root protection afforded by Regent was particularly acute. We believe that Regent 80WG is very susceptible to performance problems when densities of corn rootworm larvae result in root injury in the 4.0-or-greater range on the Iowa State root-rating scale. During the past 2 years, we have seen root pressure of this magnitude in many of our on-farm cooperators' fields throughout east-central Illinois. Bottom line: We believe that producers who use Regent 80WG better hope for low to moderate rootworm densities in 1998. If we get another "rootworm season" like 1997, growers shouldn't expect too much from Regent 80WG when it comes to rootworm protection.

Table 1. Root ratings (RR)1 for Regent 80WG applied in furrow (microtubes) at 0.13 lb. (AI)/acre at DeKalb, Monmouth, and Urbana, 1996 and 1997. Other insecticides listed were the "best" performers in respective trials.

Lorsban 15G2.25Counter 20CR2.15Fortress 5G2.13
Regent 80WG2.85Regent 80WG3.10Regent 80WG3.53
Check4.15Check4.38Regent 80WG
+10-34-0 (0.67 qt/A)
Fortress 5G3.10Aztec 4.7G3.35Counter 20CR3.30
Regent 80WG4.45Regent 80WG5.10Regent 80WG4.55

1Iowa State root-rating scale: 1, no visible damage or only a few minor feeding scars; 2, some roots with feeding scars but none eaten off to within 1.5 inches of the plant; 3, several roots eaten off to within 1.5 inches of the plant but never the equivalent of an entire node of roots destroyed; 4, one node of roots destroyed or the equivalent; 5, two nodes of roots destroyed or the equivalent; and 6, three or more nodes of roots destroyed.

Regarding the performance of Regent 80WG against European corn borers, results from University of Illinois trials suggest this product does offer some protection against moderate levels of pressure. However, producers should consider carefully which insect pest most threatens the bottom line in 1998. There are rescue treatment options for European corn borers, but fewer satisfactory alternatives when it comes to rescue treatments for corn rootworms.

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