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Seed Treatments and Corn Rootworm Protection: Buyer Beware

March 16, 2001
As producers continue with preparations for spring planting, many are still unsure what to expect from seed treatments regarding corn rootworm protection. Although we have been very clear on this issue, questions continue to linger. Last year, in several issues of the Bulletin (17, 19, and 24), we provided data that indicated ProShield and the 1.3 milligram per seed rate of imidacloprid (Prescribe) did not provide consistent root protection at moderate to heavy infestations of corn rootworms. Please refer to the following Web site for more complete information on the efficacy of these seed treatments against corn rootworms in University of Illinois trials that were conducted in 2000: evaluations/eval-2000/corn-rootworm.htm.

Last fall, we also presented efficacy data (Bulletin 24) from Iowa State University that pointed out the inconsistent nature of ProShield and Prescribe against corn rootworms. In 2000, ProShield and Prescribe provided only 22% and 9% consistency ratings, respectively, when averaged across six test locations in Iowa. Consistency was based on the percentage of times a product limited the node-injury rating to no more than 25% of a single node. Using this same benchmark, consistency ratings for other soil insecticides were as follows: Force 3G, T-band--96%; Aztec 2.1G, T-band--96%; Fortress 5G, T-band--95%; Force 3G, furrow--94%; Counter 20CR, T-band--89%; Fortress 5G, furrow--86%; Lorsban 15G, T-band--83%; Counter 20CR, furrow--76%; Capture 2EC, T-band--75%; Thimet 20G, T-band--66%; and Regent 4SC, furrow, microtube--51%. Consistency in the check was 13% and not statistically different from either ProShield (22%) or Prescribe (9%).

These data, along with data from other university trials in the Corn Belt, clearly point out that seed treatments do not offer consistent corn-root protection against corn rootworm larvae. Potential buyers should be fully aware that depending on these products to provide consistent corn rootworm control could be a costly mistake. It is our opinion that these seed treatments, as currently designed and marketed, are not up to the challenge of protecting roots from injury against moderate to heavy pressure by corn rootworm larvae. Because most fields are never scouted, producers are typically poorly equipped to decide which fields support heavy to moderate infestations versus those fields with low infestations of corn rootworm larvae. So, the great majority of producers take out an "insurance policy" against corn rootworms. Make sure your coverage is up to speed.

For additional information on the performance of these seed treatments against corn rootworms, please go the following Web site: 2001/Article1/index.htm.

--Mike Gray and Kevin Steffey

Author: Kevin Steffey Mike Gray

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

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