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Stalk Borer Management: Role of Bt Corn

June 21, 2002
This year we received quite a few calls concerning stalk borer injury to corn. As producers know, managing stalk borers is a tricky business. In many instances, stalk borers are ignored until plants begin to show some of the classic signs of infestation, such as "dead-heart" injury. We also know that it is key to kill stalk borer larvae as they leave their weed hosts to prevent them from tunneling into nearby corn plants. We've stressed that good weed management practices often prevent economic infestations of stalk borers. Having laid out these stalk borer management basics, we also know that this insect species proves frustrating for many farmers each year. Thus, the question: Will Bt hybrids prevent stalk borer damage?

A paper published (June 2002) by two Iowa State entomologists (Rachel Binning and Marlin Rice) in the Journal of Economic Entomology (vol. 95, no. 3) took a very close look at this question. They evaluated the efficacy of two genetic events (event Bt 11-Cry1Ab and event CBH351-Cry9C). The scientists infested two transgenic hybrids and their "non-Bt near isogenic" lines with stalk borer larvae (first through fourth instars). Each hybrid was infested with a specific stage of instar at three growth stages (V1, V3, and V5). Results from the paper offer good insights regarding the potential usefulness of Bt hybrids for management of this frustrating insect pest of corn. The authors offered the following concluding remarks in the discussion section of their paper: "Although Bt corn does not eliminate stalk borers, farmers planting Bt corn to control the European corn borer may benefit from reduced stalk borer infestations, especially if the larvae are first or second instars and the corn plants are at stage V3 or older. The reduction in numbers of stalk borer would be more significant when combining Bt corn with other management techniques, such as mowing or burning grassy areas in the spring and encouraging the presence of natural enemies."

We will continue to learn more about the role of transgenic plants and other pest management tactics used in combination to manage a variety of insect pests of field crops.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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