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Bt corn lines added to hybrid mix

The next few years could prove very complicated for corn producers as they painstakingly search for the perfect hybrid for their fields.

“We're in a transition year right now, so it can be confusing,” says Kathy Flanders, Auburn University Extension entomologist, referring to the new Bt products on the corn market this year. “These Bt products protect us against various pests. We've got some new products that'll be with us for a few years, and there will be even different ones in another few years. So right now, we have the old stuff, the new stuff and the older stuff.”

These Bt products are not all created equal for the different kinds of corn insect pests in Alabama, she says. “Some are designed for different things that you don't have in your area, and you might not need that particular Bt technology,” said Flanders, speaking at the recent Central Alabama Corn Production Meeeting held in Autaugaville.

According to the Alabama Cooperative Extension System Corn IPM for 2009, corn has been genetically engineered to produce Bt toxins that are effective against caterpillar insects such as European corn borer, Southwestern corn borer, and lesser cornstalk borer. Bt corn can also help protect corn against attack by corn earworm and fall armyworm. It is marketed under such names as YieldGard for corn borers (Cry1Ab protein), “Bt” (Cry1Ab protein), CB YieldGard (Cry1Ab protein) and Herculex I (Cry 1F protein).

All of these hybrids express the Bt protein throughout the plant.

Results from tests in Alabama show Bt corn for corn borers is most likely to pay off in two situations:

  • In north Alabama, in areas where there are chronic problems with stalk borers such as the Southwestern corn borer (yields of Bt corn were approximately nine bushels per acre greater than yields of non-Bt corn in 2004).

  • In years when corn must be planted after recommended planting dates (tests in Baldwin County indicated that fall armyworm pressure is sufficiently high for Bt corn to be profitable when planted in March).

Bt corn for corn borers can be planted on up to 50 percent of the total corn acreage. There must be a 50-percent non-Bt corn refuge. In 2009, some of the Bt corn will require only a 20 percent refuge. “Refuge requirements are changing, so pay attention,” says Flanders.

Some of the new types of Bt corn are effective against other caterpillars such as fall armyworms and corn earworms. Currently available varieties of Bt corn are effective against the root-feeding larvae of corn rootworms, particularly the western corn rootworm.

The genes in this genetically engineered corn are different from those conferring resistance to corn borers and other caterpillar pests, says Flanders. Sometimes, the two types of genes are stacked in a hybrid — like in Herculex Xtra or YieldGard Plus, for example — in order to give the plant resistance to rootworms and caterpillars such as the corn borer.

Western corn rootworm is a pest of continuous corn in the northern half of Alabama. This is where planting a hybrid with a rootworm Bt gene is most likely to pay off, says Flanders. Bt corn for rootworms is not effective against Southern corn rootworm.

When growers are ordering corn seed or looking at reports, they need to understand the full name of the product and what that product does. “There are a lot of hybrids out there that are stacking the corn borer and the rootworm traits. You might not need the stack, but if that's all you can get from your seed dealer, and they won't charge you more for a certain trait, then a stacked gene variety would be okay to use. Just think about which traits are most useful for your area,” she says.

“The next few years could prove to be confusing as far as corn hybrids go, says Flanders. “Be an informed consumer, and find out what's in that seed bag.”

In corn trials conducted in southeast Alabama's Wiregrass region this past year, some of the hybrids with Bt traits showed a decrease in aflatoxin contamination, says Austin Hagan, Auburn University Extension plant pathologist.

“We had a number of varieties with Bt traits, and they were planted early with a lot of corn earworm and fall armyworm activity. We're still looking at these and clarifying which traits they had, but we saw a decrease in aflatoxin contamination in some of the varieties compared with others. In the ones with corn earworm and fall armyworm traits, the aflatoxin levels dropped down some. That's a secondary benefit,” says Hagan.

A large project is currently under way in the Southeast to specifically address the aflatoxin problem in corn, he says. “There are a lot of issues with aflatoxin showing up in corn now,” he says.

TAGS: Corn
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