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.
"It remains to be seen how the rest of this growing season will play out," said Gray. "For now, it makes sense to monitor this unfolding situation carefully and pay attention to the performance of Bt hybrids this season."
Longer term, it will be increasingly important to integrate management practices such as: 1) the rotation of corn with other crops, 2) rotation of Bt traits from season to season, 3) the use of a non-Bt hybrid along with a soil insecticide at planting, and 4) use of refuges when planting a Bt hybrid.