A brave new cotton is getting mixed reviews as its first big Georgia harvest approaches. But any critique is too early until all the cotton is picked, says a University of Georgia Extension Service expert.

"We still have many growers who are very happy with the product," said Phillip Roberts, an extension entomologist. "However, we also have some who are displeased. But we won't really be able to evaluate it until the harvest is in and we know what kind of yields we've got."

The new cotton is a modern wonder. Using genetic engineering, scientists inserted a gene from a bacterium, Bacillus thuringiensis, into cotton plants. This Bt gene allows the plant to produce a toxin common in nature. In a sense, the new cotton grows its own insecticide.

The toxin is deadly to tobacco budworm and helps control corn earworm, the two main insect pests of Georgia cotton.

So far, growers' assessment of Bt cotton varies from place to place. But Roberts said it's not over until the cotton is picked. The harvest is Bt cotton's final exam.

"We may still have better yields with Bt cotton because of the bollworm control it provides," he said. "So we can't really give it a final grade until then."

The Boll Weevil Eradication Program chased the worst cotton pest, the weevil, out of Georgia by 1994. "Since then, our farmers have spent more money controlling tobacco budworm and corn earworm than all others combined," Roberts said.

The two caterpillars are both called bollworms when they attack cotton.

"You really can't distinguish between the two when they're small," Roberts said. "When they're adults, though, you can."

Bt cotton made its debut this year across the cotton belt. The seed cost growers more than normal varieties. But they figured to come out ahead, since they wouldn't have to spray costly insecticides to control bollworms.

That hasn't been entirely true, partly because of an oddity among bollworms.

"Tobacco budworm is more susceptible to Bt than corn earworms," Roberts said. "Normally we have a fairly even mix between the two. But this year the population is skewed heavily toward corn earworms."

No one knows what happened. "Something happened over a large area of the cotton belt that reduced tobacco budworm populations," Roberts said. "But we don't know what that was."

The result is that Bt cotton's control of bollworms has disappointed some growers.

"We have some Bt cotton that hasn't been sprayed at all for bollworms," he said. "In other areas, growers have had to spray once, and sometimes twice."

Statewide, Roberts said, farmers have had to spray for bollworms in about a fourth of the Bt cotton. "One of the things we've learned this year," he said, "is that Bt cotton isn't immune to bollworms."

Some conventional cotton fields haven't had to be sprayed this year. Others have been sprayed up to six times. The state average, Roberts said, is probably around three sprays.

If Bt cotton does prove successful, it could add to the supply U.S. farmers grow. But it may not affect the price of cotton products at the store.

"The main benefit would be a lower cost to farmers," Roberts said. "That would give them a better profit for all the work and risk of growing cotton."