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Texas Panhandle Corn Rootworm Probably Resistant to Some Bt Corn
There were a crazy lot of western corn rootworm beetles emerging from continuous corn fields this summer in the Texas Panhandle, and with seed purchase decisions on the horizon it might be a good idea to talk about Bt resistance. For two years now, Dr. Ed Bynum, Extension Entomologist in Amarillo, and I have seen extensive damage to Bt corn with the toxin mCry3a. These fields have been found in the zone from Dalhart in the north to Hart in the south. We have been seeing all the textbook symptoms of a failed Bt rootworm toxin: growers using soil applied insecticides in addition to their Bt seed, heavy root damage, plant lodging, lots of adult beetles on the wing because they were not killed as larvae feeding on roots, and aerial spraying of adult beetles to try and kill them before they clip silks or lay eggs that will become rootworm larvae the following year. This year we received phone calls from consultants around Hart that were alarmed at the huge numbers of beetle...
Bt Corn Seed Selection in Light of Resistance in Corn Rootworm
By Patrick Porter and Ed Bynum, Extension Entomologists in Lubbock and Amarillo, respectively. The August 25th edition of this newsletter discussed how our mCry3a Bt corn was no longer able to control western corn rootworm in an area from Hart, Texas, north to the top of the Panhandle. In that newsletter, even though we were seeing all of the classic signs of resistance, we used the term �probable resistance�, only because our laboratory assays on field collected beetles will not be completed until next year. In addition to mCry3a, that newsletter suggested that since there is cross resistance between all of the Cry3-type toxins (mCry3a, eCry3.1Ab and Cry3Bb1), none of these toxins could be expected to provide good control of western corn rootworm. Dr. Aaron Gassmann at Iowa State University, a leading authority on corn rootworm resistance, said, �Cry3Bb1, mCry3A, and eCry3.1Ab all appear fairly similar to the rootworm. Resistance to one is likely to confer resistance ...
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