In the first year of tests with three Syngenta Bt sweet corn varieties, Tom Kuhar, an entomologist, and Tony Bratsch, a horticulturist with Virginia Tech, reduced insecticide sprays from six to one, without compromising yield or control of European corn borer, fall armyworm and corn earworm. Corn earworm is the No. 1 pest for growers in Virginia.
Kuhar and Bratsch worked with Clifton Slade, Southeast Virginia District Extension agent and Vonny Barlow, a graduate student at Virginia Tech, on the project.
The researchers looked at three Bacillus thuringiensis (Bt) varieties from Syngenta: Bigtime, a super sweet bicolor; Prime Plus, a super sweet yellow; and Jackpot, a sugar enhanced bicolor. The varieties were tested in research plots in Blacksburg, Va., Suffolk, Va., and on the Eastern Shore.
“There’s a potential opportunity for a farmer to grow sweet corn without incurring the extra cost of controlling difficult insect pests,” Kuhar says. “The best opportunity is to plant the Bt corn early to avoid heavier moth pressure. For fall sweet corn, the pressure is intense, even with Bt corn.”
Even in untreated checks, the Bt varieties suffered only 10 percent damage from the European corn borer, compared to four to five tunnels into each non-Bt stalk. “We had roughly 80 to 90 percent of the non-Bt ears and stalks infested with European corn borer,” Kuhar told a group at the field day held at the Tidewater Research and Extension Center in Suffolk, Va., recently. “The 10 percent infestation rate in the Bt varieties was without the benefit of any sprays. In a 2000 study on the Eastern Shore, when we put on one foliar spray in fall-planted sweet corn at the heaviest moth pressure late in the season, we were able to take the number down close to zero.”
Yields of the Bt varieties were higher than their non-Bt counterparts, Bratsch says. “The varieties held up in all areas.”
A 10-percent infestation would still be acceptable for a roadside stand operator, Kuhar points out.
With non-Bt varieties, “a farmer has to spray at least every two to three days to control these pests,” Kuhar says. “It’s an intensive spray schedule upwards of six sprays using pyrethroids from silking through the maturity stage. Farmers can tell you that if there’s bad weather coming through, they don’t always get the chance to make the timely applications that are needed to control these insects.”
“There’s a lot of potential for small, roadside growers who might not have the time or the right equipment to spray on a timely basis,” Bratsch says. “Producers in Georgia and Florida are growing Bt varieties widely.”
Based on surveys, the researchers say they haven’t seen consumer objections to buying Bt sweet corn.
Producers who raise Bt sweet corn must purchase at least a bag of the varieties and report the acreage they grow to manufacturer, the researchers say.