The following information is a Web Extra from the pages of Farm Journal. It corresponds with the article "Resistance Reality." You can find the article in Farm Journal's 2012 Seed Guide.
Read a copy of the entomologists’ letter to EPA. (PDF)
Bt Corn Root Injury Confirmed in Illinois
By Susan Jongeneel, University of Illinois
In early June, University of Illinois professor of entomology and crop sciences Extension coordinator Mike Gray reported that the western corn rootworm season began extremely early this year.
Reports of severe injury to Bt corn that expresses the Cry3Bb1 protein targeted against corn rootworms have come in from western Cass County. In 2011, similar reports of injury to Bt hybrids expressing this protein surfaced in other North Central states, particularly in Iowa.
"Thus far, resistance to this protein in Illinois has not been confirmed," said Gray. However large numbers of western corn rootworm adults were visible in the whorls of plants in Cass County.
Gray shares his thoughts with University of Illinois' Todd Gleason:
Roots were removed randomly from this field and from a nearby field that also had been planted to a Bt hybrid expressing the Cry3Bb1 protein. Roots from both fields exhibited feeding injury with more injury in the second field, although fewer beetles were observed there. Because adults were not as noticeable in the second field and emergence was just beginning in the first field, root feeding is expected to continue in both fields.
No lodging was observed, probably because the plants were short and the soil was hard and dry. "However, as root feeding continues and plants become taller, lodging should be expected, especially if storms with rain and winds materialize," said Gray.
On June 8, the plants that had been evaluated for root injury were checked for the expression of the Cry3Bb1 protein at the University of Illinois laboratory. All tested positive. This does not mean that a resistant western corn rootworm population has been confirmed in Illinois. The registrant of this technology has been notified and will conduct some follow-up investigations in these fields.
At this point, it is not clear why performance challenges of some Bt hybrids expressing this protein are continuing. However, producers should remain vigilant during this growing season and report any performance issues with corn rootworm injury on their Bt hybrids.
Like the fields that had Bt performance issues last year, the fields in Cass County had been in continuous corn for many years (at least 10 consecutive years). Moreover, the same trait (Cry3Bb1) had been used since 2007 (six growing seasons). Under these conditions, the selection pressure for resistance development is increased markedly.