10/29/99

Contacts:
Marlin Rice, Entomology, (515) 294-1101
Megan Kuhn, Agriculture Information, (515) 294-2957

ISU RESEARCHERS FIND FARMERS REDUCE INSECTICDE USE WITH BT CORN

AMES -- Twenty-six percent of Midwest farmers planting Bt corn in 1998 decreased their insecticide use for control of European corn borers, according to a survey conducted by two Iowa State University researchers.

"This is one of the main benefits of planting genetically-engineered corn -- broad-spectrum insecticide use has greatly decreased," said Marlin Rice, entomology professor. "This should result in an improvement in environmental quality."

Rice and Clinton Pilcher, entomology graduate student, surveyed 2,000 farmers from six states who planted Bt corn in 1998. They contacted farmers from Illinois, Iowa, Kansas, Minnesota, Nebraska and Pennsylvania.

The survey asked about insecticide use in 1998 compared with use in previous years. During the first three years Bt corn was commercially available, the percentage of Bt corn growers who said they reduced their insecticide use increased from 13 percent in 1996, to 19 percent in 1997 and to 26 percent last year.

In 1998, 18 percent said their insecticide use stayed the same; 2 percent said it increased; and 54 percent did not use insecticides.

Bt corn contains a gene from Bacillus thuringiensis, a soil bacterium that produces a protein that is toxic to some insects including the European corn borer. When the insects feed on Bt corn leaves and stalks, they die.

One concern with Bt corn is the chance that insects may become resistant to the toxin. Seed companies and university researchers are studying ways to delay this from happening through resistance management strategies.

The ISU survey asked farmers if they would follow a recommended resistance management program strategy and almost 85 percent said yes. "This shows us that farmers are willing to use the technology correctly," said Rice. "They know the benefits and are not willing to waste the technology by misusing it."

Other findings from the survey include:

• 82 percent said their primary reason for planting a Bt corn hybrid was to prevent yield loss from the European corn borer, while 27 percent wanted to eliminate the need for insecticide to control the insect. (Farmers could choose more than one reason.)
• From 1991 to 1995, before Bt corn was introduced, 41 percent said they did nothing to guard against the insects; 24 percent used insecticides to minimize yield losses.
• Forty-five percent rated yields of Bt corn as higher compared to similar maturity non-Bt hybrids planted about the same time; 41 percent said yields were similar; and 7 percent said they were lower.
• After seeing the yields from Bt corn fields, 41 percent said European corn borers caused more yield loss than they'd previously thought; 29 percent said yield loss was what they expected; and 12 percent said yield loss was less than they expected.
• Thirty-seven percent said the economic return from planting Bt corn was slightly better compared to similar non-Bt hybrids; 26 percent said it was similar; and 16 percent said it was worse.

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