Will planting Bt corn pay off in recommended time plantings in Georgia? In certain situations, says University of Georgia entomologist David Buntin.

“Most corn in Georgia is planted at the recommended planting time of March through mid-May depending on the region for the state,” says Buntin.

“In most years, this corn avoids serious insect damage. However, the main target pest in recommended plantings throughout the state is corn earworm, which often exceeds 50-percent infested ears.”

Fall armyworm damage to whorls usually is avoided in early plantings, but it can be significant in outbreak years, he adds.

“In most years, the risk of damage by fall armyworm in recommended plantings is greatest in the southernmost tier of counties and in the southwest corner of Georgia. Growers must weigh the added cost of the Bt trait(s) being considered against the historical risk of serious whorl defoliation or ear damage by insects in on-time plantings.”

There are three situations, says Buntin, where planting hybrids containing Bt traits provides a clear benefit:

Situation 1.Corn statewide that will be planted after the recommended planting date. The risk of damage by fall armyworms, corn earworms and stalk borers increases the later you plant.

Reduces risk of insect damage

Bt technology reduces the risk of insect damage, thereby allowing for later plantings, although late plantings have lower yield potential and increased risk of damage by diseases.

Studies in 2009-2011 compared the yield of hybrids with single trait YieldGard — corn borer and Genuity VT3 PRO to a similar non-Bt hybrid in trials planted at the recommended and late planting times at Plains and Tifton, Ga.

In trials at the recommended planting time, hybrids with Genuity VT3 PRO averaged 0.96 bushels per acre more than the hybrids with YieldGard-CB and 2.35 bushels per acre more than non-Bt hybrids.

A more consistent response occurred in trials at later planting times where hybrids with Genuity VT3 PRO averaged 4.10 bushels per acre more than hybrids with YieldGard — CB and 9.11 bushels per acre more than non-Bt hybrids.

Situation 2. Northwest Georgia including the Limestone Valley, which consistently has high corn borer populations.

Several species of corn borers occur in Georgia, but corn borers normally do not reach damaging levels throughout most of the state. The exception is northwest Georgia including the Limestone Valley.

In this area, the Southwestern corn borer occurs and it usually is worse in corn after corn in later plantings, but can damage rotated corn planted on time.

While yield response varies with infestation level, trials near Calhoun, Ga., found a 5 to 15 bushel-per-acre response to YGCB Bt corn. More recent studies in northern Alabama found a 9 bushels per acre advantage due to Southwest corn borer control.

Situation 3.Non-rotated (corn after corn) in the northern half of Georgia, where Western corn rootworm can be a problem.

This is a very uncommon situation. There have been only a handful of fields in Georgia with damaging infestations of Western corn rootworm. All were dairy operations in the northern half of the state growing corn in the same fields for several years.

Western corn rootworm larvae attack roots mid-season. It is only a pest of continuous corn and is controlled by rotation.

As little as one year rotated out of corn every three or four years will control this insect in Georgia.

Scout fields during pollination because adults are easily seen feeding on silks and tassels. Bt rootworm traits are very effective.

To get rootworm traits, you will need to plant a stacked product with a rootworm trait. Bt rootworm traits do not control wireworms, white grubs, or Southern corn rootworm in the seedling stage.

(Researchers across the South are trying to get a handle on the relative merits of Bt corn in the area. For a look at the situation in Alabama, click here. There have also been reports of insect resistance developing in Bt corn planted in the Midwest. Southern growers are being urged not to ignore that threat. For the story, visit http://southeastfarmpress.com/grains/don-t-ignore-resistance-threat-rootworms-bt-corn).

phollis@farmpress.com