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Issue No. 22, Article 1/September 2, 2005

Preliminary Root-Evaluation Ratings Available for DeKalb and Urbana Corn Rootworm Product Trials

The preliminary root-rating results have been analyzed for two of our corn rootworm product efficacy experiments (DeKalb and Urbana; Table 1). Data from a third trial (Monmouth) are still being evaluated. We look forward to sharing the results from the Monmouth study in our next issue of the Bulletin. As you review these data, please keep in mind that our studies are conducted on corn plots that have been planted into a trap crop (late-planted corn in 2004 interplanted with pumpkins). By using a trap crop, we purposefully place corn rootworm products under intense pressure. Although it is less common to witness root injury as intense as occurred in our experiments, many of us have observed severe root damage and lodging in producers' fields through the years, including this season. We believe the results from our trials better enable producers to make the most informed choices regarding product selection for corn rootworms.

Root-injury ratings in our checks at DeKalb and Urbana were nearly identical: 2.37 and 2.32, respectively. These root-rating averages indicate that 2-1/3 of nodes were destroyed on plants within our check treatment at each site. A preliminary review of these root-rating data from DeKalb and Urbana suggests the following:

  • The granular soil insecticides performed very well under intense corn rootworm larval pressure.
  • Root-rating averages (DeKalb and Urbana) in the Poncho 250 plus Aztec 2.1G treatment were not statistically different from the Aztec 2.1G treatment alone.
  • Root-rating averages in the Capture 2EC and Regent 4SC treatments were not satisfactory (nearly 1-1/2 nodes of roots destroyed). The Regent 4SC treatment in Urbana was not statistically different from the check. Although Lorsban 4E performed better in DeKalb (1/2 node destroyed), nearly a full node (0.91) of roots with this treatment was pruned in Urbana. The Lorsban 75WG treatment had root injury that nearly equaled 1-1/2 nodes of roots pruned in both DeKalb and Urbana.
  • The Cruiser Extreme treatment did not protect roots at either location and was not statistically different from the check in either DeKalb or Urbana.
  • The Poncho 1250 treatment provided statistically better root protection than the check in both experiments. Root pruning in the Poncho 1250 treatment at DeKalb was slightly less than 1 node of roots pruned (0.78), whereas in Urbana, slightly more than 1 node of roots were pruned (1.21).
  • The YieldGard RW treatment in Urbana provided excellent root protection. In DeKalb, more root pruning, particularly on brace roots, was observed in the YieldGard RW treatment with nearly 3/4 of a node destroyed.

Overall, these results are somewhat similar to what we have observed in previous years for a number of the treatments. Despite the very dry soil conditions this summer, the granular products provided very good to excellent root protection. Corn rootworm products will continue to be challenged more intensively as planting dates are pushed back earlier and earlier in the spring. The importance of proper calibration and incorporation cannot be overemphasized for the soil insecticides. In an upcoming issue of the Bulletin, we will share the root-rating results from the Monmouth experiment and offer additional information on late-season brace root feeding in the YieldGard rootworm treatment that we've observed in both 2004 and 2005 in some of our experiments.--Mike Gray, Ron Estes, and Kevin Steffey

Kevin Steffey
Mike Gray
Ron Estes

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