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Preliminary Root-Rating Results from Insecticide Efficacy Trials Available

September 6, 2002
The preliminary root-rating results from the 2002 insecticide efficacy trials are provided for DeKalb, Monmouth, and Urbana in Table 1 and Table 2. Root feeding was most intense at the DeKalb site (control = 4.65) with approximately 1 1/2 nodes of roots destroyed in the untreated check. Roots from the check treatment at Monmouth and Urbana averaged approximately 4.0 (one node of roots destroyed) on the Iowa State 1 to 6 root-injury scale. At the DeKalb location, most products failed to keep root injury below a rating of 3.0 (some pruning, but less than one node of roots destroyed), the so-called economic injury index.

Performance of the liquid treatments at DeKalb, Regent 4SC (root rating = 5.05, consistency rating = 0%) and Capture 2EC (root rating = 4.50, consistency rating = 5.0%), were particularly troublesome. Conditions at DeKalb were very hot and dry throughout much of the summer. These findings seem to suggest that under adverse environmental conditions (very dry soil conditions) accompanied by large densities of corn rootworm larvae, growers may be less than pleased with these two liquid products. Root-injury ratings for the insecticide treatments were lower at the Monmouth and Urbana experiments; however, the level of rootworm pressure was less intense. So this is to be expected. Most products kept root injury below a rating of 3.0 at these locations.

There were exceptions. Regent 4SC and Capture 2EC again did not perform very well, particularly in Urbana with root ratings of 3.85 (consistency rating = 50%) and 4.32 (consistency rating = 28%), respectively.

In 1998 I spoke at the Crop Protection Technology Conference and suggested that almost any insecticide product will "stumble" from time to time. In fact, I compared the use of a soil insecticide with the "roll of dice." In recent years, considerable interest has been focused on the efficacy of new liquid products and seed treatments. To date, consistency of these new approaches has been lacking. Under the right of set of conditions, product performance of any soil insecticide is likely to be compromised. These include early planting (first week of April), delayed corn rootworm larval hatch (second week of June), hot and dry soil conditions (particularly during pollination in July), and large numbers of corn rootworm larvae. The bottom line is that producers take a chance when they purchase a soil insecticide because none of the products are "rootworm proof." No wonder there is so much interest in the potential registration of transgenic corn rootworm hybrids. They too will provide a unique set of challenges for producers.--Mike Gray

Author: Mike Gray


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

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