Bt corn has had a heap of hype the past three years. But how has it done under the gun?
By nearly all counts, it has lived up to its promise, say university entomologists and seed company officials.
Bt hybrids had their first wide-scale planting in 1997 - a banner year for corn borers.
Not all Bt hybrids had the same type of protection (genetic event) last year. The four genetic events registered with EPA were: 176, used by Mycogen as NatureGard and by Novartis as Knockout; DBT418, used by Dekalb as Bt-Xtra; and BT11 and MON810, trademarked as YieldGard and used by several companies. YieldGard provides longer-season and fuller-plant protection than the others.
AgrEvo's Starlink event was used on an experimental basis last year.
"In general, Bt hybrids performed very well in 1997 under the heavy corn borer pressure," reports University of Minnesota extension entomologist Ken Ostlie. "We saw yield advantages of 15 to 20 bu/acre with Bt hybrids vs. their non-Bt counterparts. In scattered areas there were up to 70-bu differences."
Some corn borers survived on plants with the NatureGard, Knockout and Bt-Xtra events in 1997, says University of Nebraska entomologist John Foster.
"But keep in mind that there was extremely heavy corn borer pressure, and that borer survival doesn't mean failure," Foster emphasizes.
He notes that YieldGard provided full-season, full-plant protection, as advertised.
"AgrEvo's Bt technology supplied protection close to that of YieldGard," Foster reports.
Kevin Steffey, University of Illinois extension entomologist, says 1997 research showed that most Bt hybrids provide excellent control of borer larvae. It also revealed that the corn yields well if the Bt gene is in a hybrid with high yield potential. And that a Bt hybrid can yield acceptably even if infested with corn borers late in the season.
Pioneer research at 18 locations last year revealed a yield advantage for Bt hybrids (YieldGard) over similar hybrids without the Bt gene. The difference ranged from 5% with low corn borer infestation to 20% with severe infestation, says Steve Butzen, Pioneer agronomy information specialist.
"In 1997, in areas where 40% of the plants were attacked, we saw a 6-bu/acre increase with Bt hybrids," says Michael Wojtalewicz, Asgrow corn product manager. "It was a heavy corn borer year, and there was, across all sites, a 10.8-bu/acre advantage for Bt hybrids vs. their isolines (non-Bt counterparts)."
Dekalb Genetics has three years of data confirming that a Bt hybrid, even if infested late with borers, can yield competitively.
"Hybrids containing the same base germplasm, but different Bt events, either YieldGard or Bt-Xtra, have produced similar yields under similar corn borer pressure," reports Tracy Klingaman, Dekalb product manager.
Gene Kassmeyer, Garst product manager, says that his company in 1997 had some experimental hybrids with YieldGard and some with AgrEvo's Starlink.
"Both types gave full-season, full-plant protection," he states.
After hammering the corn crop last year, borers were virtual no-shows in 1998.
Planting delays in much of the Corn Belt meant there weren't many egg-laying opportunities for first-generation moths. And heavy rains destroyed many larvae that did hatch.
There were, however, a few areas with moderate to heavy borer pressure, reports Dekalb's Klingaman. "In Missouri, DK626Bt (Bt-Xtra) outyielded DK626 (non-Bt) by 26 bu/acre."
Asgrow's Wojtalewicz says Bt plants, in the scattered areas of heavy pressure, definitely were healthier than their non-Bt counterparts.
Minnesota's Ostlie points out that 1998 data will reveal how Bt hybrids perform when there is lack of corn borer pressure.
In view of light borer activity in 1998 and the faltering farm economy, should farmers shell out the extra money for Bt seed in 1999?
"There is not a good correlation between corn borer population from one year to the next," replies Illinois' Steffey. "High-density years often are followed by low-density years and vice-versa. Using Bt hybrids for corn borer management should be a long-term investment. The decision should not be based on what did or didn't happen the year before."
Steffey points out that there have been more borer outbreaks in the past 10 years than in any previous period. He attributes that to increasingly earlier planting and longer-season hybrids.
"When first-generation moths fly, there are corn plants at the right stage for egg-laying," he says. "Last spring, with the planting delays in many areas, was an exception."
Ostlie says that Minnesota has been having heavy corn borer pressure three out of eight years.
"For 1999, in light of those odds, each farmer will need to decide how much Bt insurance he or she can afford. Maybe it will be better to plant non-
Bt corn and scout. Or perhaps the best bet is to split the acreage."
Nebraska's Foster reports that corn borers are the rule rather than the exception for that state.
"In seven or eight years of 10, some type of control is needed," he says. "Long-term, Bt technology pays for itself."
It's rare in many areas to have two consecutive years of low borer numbers, says Garst's Kassmeyer. "Therefore, I would say the odds of Bt corn paying off in 1999 are 70-80%."
If you decide to plant Bt corn, entomologist Foster stresses that you choose your hybrids on performance - yield, disease resistance, stalk integrity - not on the type of Bt protection.
"All the events are effective - make genetics your first consideration," he states.