Cooperative
Extension
Service


University of Illinois
at
Urbana-Champaign


No. 1/March 21, 1997

Results for 1996 Corn Rootworm Soil-Insecticide Efficacy Trials

The spring of 1996 was wet and cold, and corn rootworm egg hatch was delayed until mid-June across much of Illinois. This was the second consecutive year in which a very cool spring caused egg hatch to occur about 2 weeks later than "normal." Normal anymore is beginning to be nothing more than an average of 10 years of extreme weather temperature and rainfall data. Because egg hatch was delayed, we discovered that rootworm larval injury evaluations conducted on July 15 at Urbana and July 31 at DeKalb were too early to detect peak levels of rootworm injury. So, to extend the fun of root digging, we dug the Urbana and DeKalb sites again on August 2 and August 19, respectively. The root-rating information presented in Table 1 is from the second set of root digs for DeKalb and Urbana. We were able to evaluate the soil insecticides only once at the Monmouth site.

There were no big surprises in the performance of the soil insecticides during 1996. In general, satisfactory levels of protection were offered by the registered products listed in Table 1. The average root ratings from in-furrow treatments of Aztec 2.1G and Force 3G at the Urbana site increased one full rating (an increase in damage) compared with the average root ratings from band-application treatments. For years, university trials across the Corn Belt have shown that band applications of soil insecticides typically outperform in-furrow treatments. Such was the case in our trials for 1996. Furadan 4F did not perform well again as a broadcast treatment at the DeKalb and Monmouth sites. Thimet's efficacy was erratic; however, considering the high level of pressure at the Urbana location, it did reasonably well at that site.

In an upcoming issue of this Bulletin, we will present some additional information about soil insecticides and offer some data on consistency of root protection provided by these products.

Mike Gray, Extension Entomology, (217)333-6652

Table 1. Mean root ratings1 for 1996 corn rootworm soil-insecticide evaluations in DeKalb, Urbana, and Monmouth.

ProductRate2PlacementDeKalb3Urbana4Monmouth5
Aztec 2.1G0.15band2.602.902.25
Aztec 2.1G0.15furrow2.403.802.50
Counter CR1.30band2.402.902.15
Counter CR1.30furrow2.602.682.55
Force 3G0.13band2.40&2.652.45
Force 3G0.13furrow&2.903.652.70
Furadan 4F1.00broadcast3.87-3.80
Fortress 5G0.16furrow-SBX-2.15-
Fortress 5G0.16furrow3.402.343.00
Fortress 5G0.16band-2.45-
1.30band2.252.70&2.90
Thimet 20G1.30band2.803.103.95
Control--4.155.154.38

1The root-rating system used was the Iowa State University 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; 6, three or more nodes of roots destroyed or the equivalent.

2All rates are specified as lb a.i. per acre.

3Band and furrow applications, including SmartBox (SBX) applications, were made at planting on May 3. Furadan 4F was applied broadcast over two rows on May 30. Root-evaluation ratings were conducted on August 19.

4Band and furrow applications, including SmartBox (SBX) applications, were made at planting on May 20. Root-evaluation ratings were conducted on August 2.

5Band and furrow applications were made at planting on May 3. Furadan 4F was applied broadcast over two rows on May 30. Root-evaluation ratings were conducted on July 22.