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Issue No. 23, Article 4/October 5, 2007

Bt Corn + Soil Insecticide: What?

I feel compelled to clear up some confusion about the article "Bt Corn Plus Soil Insecticides May Prove Profitable" published in the Corn E-Digest on September 24. I was the source for the article, and I stated that "this two-pronged control strategy [soil insecticides + rootworm Bt corn] may prove profitable in the short-term for some farmers." Unfortunately, my intended emphasis on some farmers was overlooked, and my comments have been misinterpreted as a recommendation for corn farmers throughout the Corn Belt. Not so; in fact, not even close. At the end of the article, I indicate that using two modes of action is an insect resistance management practice that might slow the resistance to both modes. However, I added that using a soil insecticide + rootworm Bt corn as a long-term strategy would expose corn rootworm populations to the same two modes of action every year. If corn rootworms were able to survive this protection, we would face some potentially serious consequences. Nonetheless, our preliminary rootworm research evaluations, published in issue No. 21, August 17, 2007, of the Bulletin , showed clearly that plots at our Urbana location treated with Counter 15G + YieldGard VT hybrid DKC 61-69 had significantly less rootworm injury (mean node-injury rating of 0.07) than all three rootworm Bt corn hybrids, which had mean node-injury ratings of 0.84, 0.49, and 1.04 for YieldGard VT, HxXTRA (Pioneer 33T59), and HxXTRA (Mycogen 2T787), respectively. This difference in root ratings did not occur at our DeKalb and Monmouth locations.

My comments about soil insecticides + rootworm Bt corn were not intended as a recommendation. However, we are aware that some growers have combined or are contemplating combining these two rootworm control tactics, so we examined it for ourselves. At our Urbana research location where root injury to rootworm Bt corn has been greater than anticipated, the combination of Counter and a rootworm Bt corn hybrid improved the level of root protection over using a rootworm Bt corn hybrid alone. So this combination represents a potential solution for some growers, but certainly not for the vast majority of growers. Some of my colleagues in other states clearly point this out in the article titled "Double-Barreled Rootworm Control Won't Pay In Most Cases" in the October 1, 2007, issue of Corn E-Digest. I agree with them.--Kevin Steffey

Kevin Steffey

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