As southern growers get used to having more corn on their former cotton acres, they are finding that Bt corn can work as well as Bt cotton to control insect damage.
Many southern growers are still new to corn in their rotations. David Buntin, University of Georgia grain crops entomologist, reminds them that YieldGard Corn Borer (YGCB) and Herculex I target caterpillar pests, including European and southwestern corn borers, fall armyworm, corn earworm and other Lepidopterans.
Several types of Bt rootworm, YieldGard Rootworm (RW), YieldGard-VT RW, Herculex-RW and Agrisure RW are active against rootworm larvae. Rootworm Bt products are not effective against wireworms, white grubs or southern corn rootworm in the seedling stage, says Buntin.
J.K. Bordelon, a Moreauville, LA, corn, soybean and cotton producer, planted about one-third of his corn acres to Bt in 2008, including some hybrids that were stacked with glyphosate. He saw the benefits of Bt right away.
“I haven't had to treat for worms or borers since I started planting Bt,” says Bordelon, referring to acres planted in the biotech varieties.
Kathy Flanders, Auburn University Extension entomologist, says Bt corn has proven its worth in fighting Alabama borers. “In the corn borer class of Bt, they are designed for European corn borer,” (not southwestern corn borer specifically), she says. “We don't see much of that in Alabama. But we do have southwestern corn borer in parts of the state. And the Bt has been a huge help for this chronic problem. It has worked really well.”
In Mississippi, Bt corn effectively controls both southwestern and European corn borers, according to Mississippi State University (MSU) Extension entomologists.
“Bt hybrids are very effective for controlling corn borers in Mississippi,” says Chris Daves, MSU Extension entomologist.
BORDELON, WHOSE CORN averages 150-160 bu./acre in dryland production, says other insects may call for in-season pesticide applications. “We see stink bug outbreaks about half the time,” he says. “We treat them with an aerial pyrethroid application.”
Bordelon also uses aerial pyrethroid applications to treat for borers or earworms on acres outside the allowable Bt treated area. Unlike northern growers who usually face a 20% refuge when planting Bt corn, southern growers can only plant half their corn in Bt, mainly because of the larger number of Bt cotton acres.
“Growers respect the refuge and understand its importance,” says Daves.
Buntin says the 50% refuge requirement for the corn borer-type Bt is a substantial obstacle to wider adoption. “Most of the Bt corn in Georgia is used in later-than-normal plantings where the risk of insect attack is increased and probably is not more than about 15% of the total acreage,” he says.
The National Corn Growers Association notes that the environmental benefits of Bt corn and other crops are many, including the elimination of more than 46 million pounds of pesticides used on crops and countless amounts of aviation and diesel fuel for application purposes and water used in insecticide formulations.