Corn Rootworm Demonstration Plot: Evaluating the Effectiveness Corn Root Management Strategies
Agronomy & Pest Management
Rebecca Vittetoe
Extension Field Agronomist
Iowa State University Extension
Washington
Abstract
Corn rootworms can be an economic pest in corn by causing injury either by the larvae pruning the corn roots or the adults clipping the silks and interfering with pollination. From a root feeding perspective, it is estimated there is a 15% yield loss for each node pruned back to within 1.5 inches of the stalk. To help producers better understand different management strategies and to look at a new type of host plant resistance for corn rootworm called RNAi, a corn rootworm demonstration plot was established at the Iowa State University (ISU) Southeast Research and Demonstration Farm (SERF) in 2021. The demonstration plot was planted in a field at the farm that had been 15 plus years continuous corn (specifically the area used as a trap crop for corn rootworm). The trial had four treatments replicated eight times. Treatments included no management (glyphosate-tolerant only; no Bt traits or insecticide), granular soil-applied insecticide (Aztec), SmartStax®, and SmartStax® Pro (RNAi). In July, four randomly selected plants from each plot (4 plants x 8 reps = 32 roots per treatment) were dug up to evaluate root injury. Each root was tagged with the treatment and rep number. Roots were then washed by soaking in buckets of water and then power washing. The ISU 0-3 Node-Injury Scale (NIS) was used to evaluate the roots, where a rating of 1 indicates than an entire node of roots (or equivalent) was pruned to within 1.5 inches of the or stalk. In the demonstration trial at SERF, the three corn rootworm management treatments (Aztec, SmartStax®, and SmartStax® Pro) had similar average NIS ratings, and those ratings were all significantly lower than the treatment without corn rootworm management and were also below the economic threshold (0.25 to 0.5 NIS, depends on environmental conditions, corn price, and management costs). Assuming Bt resistance is not an issue, these management tactics are all good options for suppressing corn rootworm. If resistance is an issue, good alternatives would be a soil-applied insecticide, the new RNAi technology, or crop rotation.
Authors: Rebecca Vittetoe, Virgil Schmitt
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Rebecca Vittetoe Extension Field Agronomist, ISU, Iowa, 52353
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Virgil Schmitt Extension Field Agronomist, ISU, Iowa, 52761