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What's Up With All the Earworms in Bt Corn?

This is a jointly issued article from Extension Entomologists Drs. Pat Porter (Lubbock) and Ed Bynum (Amarillo). There are large numbers of corn earworm larvae in Bt corn ears in the Texas Panhandle, and some people are spraying in an attempt to control them.  The first question we are getting is what to spray, but the better question would be whether to spray.  Corn earworm is usually an ear tip feeder, and on its own is seldom an economic pest of corn. However, this year we are seeing earworms doing more than just tip damage, and feeding lower in the ear. The reason(s) for this change in behavior are unknown.  We have not forgotten last year though, when there was good evidence that just a little ear tip damage resulted in higher fumonisin levels. This could happen again this year, especially if the weather in August and September turns off wet and relatively cool. However, based on what we saw last year, the little bit of tip damage needed to promote fumonisin has alre...
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Bt Corn Seed Selection in Light of Resistance in Corn Rootworm

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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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Terms We Will Soon Use in Discussing Resistance to Bt (GM) Crops

It has been quite a challenging summer with our Bt crops on the Texas High Plains. This year we have seen huge numbers of corn rootworms emerging from many fields planted to mCry3a, a corn rootworm Bt toxin that has been used year after year in continuous corn. These fields had significant root pruning caused by rootworm larvae and produced a large number of adults � survivors of the toxin.  We have also seen corn earworm do significant damage to Bt corn that worked well a few years ago, and we have documented Bt cotton with unexpectedly high levels of bollworm damage and large larvae surviving the Bt toxins. In each case we collected insects from the field and sent them for laboratory assay to determine if the insects were resistant to the Bt toxins in the crops. These assays take time, but it is highly probable that in a few months we will be reporting that resistance has been confirmed in corn rootworm and corn earworm/cotton bollworm.  To help explain what is going on in n...
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