For the past few years, the Western corn belt has been dealing with populations of western corn rootworm that have developed resistance to two Bt genes: Cry3Bb1 and mCry3a. US-EPA has recently developed a framework for managing Bt resistance, and is requesting comments from stakeholders (see:http://www.epa.gov/oppfead1/cb/csb_page/updates/2015/extends-rootworm.html). The deadline for the comment period is April 15th.
We have not documented any cases of suspected resistance, and, in the rest of the eastern corn belt (which has been dubbed “The Fringe”), there have only been a few cases. There are many differences between the western corn belt and the fringe (for example lower rootworm populations and more crop rotation), but there are some considerations to make sure that the risk of resistance development in Ohio remains low.
The most important recommendation is rotation: most of the high-risk areas for resistance have been associated with continuous corn for more than 3 or 4 years, sometimes concentrated near diaries. If you can’t rotate your crops, a second recommendation will be rotating chemistries—it’s a good idea for insecticides AND for Bt traits. Regardless, any continuous corn should be inspected for rootworm damage by digging roots and measuring the amount of damage.
Please contact your extension educator or myself (email@example.com) if you have any cases of suspected resistance.