Daviess County Producers Demonstrate
How to Use Refuges with Bt Corn

Producers learn how to protect
a valuable pest management tool.

Bacillus thuringiensis (Bt) is one of the most widely used biological insecticides. Extremely popular with organic growers, Bt will control leaf-eating caterpillars without harming beneficial insects. Bt works by paralyzing the digestive tract of the insect larvae. Harmless to mammals, Bt can be used even on the day of harvest.

Bt technology, the incorporation of the Bt gene into corn plants, has given growers a new tool to reduce the amount of crop loss due to corn borers. One major concern that has been expressed by many researchers is that the wide use of Bt in corn plants could result in some insects developing a resistance to Bt. If this should happen, the use of one of the safest insecticides available would be lost .

Currently, the only effective way to prevent resistance is to plant some acreage with non-Bt hybrids. This is called the refuge strategy. In it, non-Bt acreage on each farm serves as a refuge, allowing some Bt-susceptible corn borers to survive. Then if a rare resistant corn borer were able to survive on a Bt-corn plant, it would most likely mate with a susceptible corn borer. Corn borers produced from this mating would still be moderately susceptible, and would not be able to survive on the Bt-hybrids. What this strategy tries to prevent is mating among Bt-resistant corn borers. Using the refuge strategy, growers must plant a portion of their corn crop in non-Bt hybrids.
(For additional information visit Bt Corn Refuges and Bt Corn.)

The success of this new technology and a heavy infestation of European corn borer and Southwestern corn borer made Daviess County growers plan to commit a high percentage of their variety selection to Bt corn. Wayne Mattingly, Daviess County Extension Agent for Agriculture and Natural Resources, working with Dr. Ric Bessin, Extension Entomologist, implemented field demonstrations to promote the use of refuges and Integrated Pest Management techniques such as crop scouting, monitoring moth flights, planting date and crop progress management, and insect damage assessments. The study involved the cooperation of five producers who planted a a Bt corn variety and included a non-Bt variety in close proximity as a refuge.

The "Bt Refuge Study" was a major part of the summer "Family Farm Field Day" which was held on a farm where one of the Bt study fields was located. Over 300 participated in the field day. As a part of the field day, Dr. Ric Bessin discussed the principles of using refuges and the cost/benefit relationship as it relates to pest management decision making.

Once harvest data was collected, the results showed that for the 1999 season little value was gained through the use of Bt varieties and the non-Bt varieties used in the refuge were economical to use as well as a sound pest management practice. Given the demonstration that refuges do not substantially affect yield, growers should be willing to implement them into their planting program.

	Original document: 23 February 2000 Last updated: 23 February 2000