Insect status good in Georgia cotton

In this fourth installment of a five-part series, Southeast Farm Press continues to look at cotton insect control trends and recommendations from the various states in the region. Presentations in this series have come from Extension entomologists in Virginia, North Carolina, South Carolina, Georgia and Alabama.

Georgia cotton producers have many effective tools — both old and new — for controlling insects, and insect pressure has been relatively light since 1997. But these are not reasons, says University of Georgia Extension Entomologist Phillip Roberts, for growers to let down their guards.

“Our status today is a good one,” says Roberts. “But we must remain vigilant about things such as scouting and staying up-to-date on control practices.”

In the past 15 years, he says, insect management has changed tremendously in Georgia and in the Southeast. “We all know what boll weevil eradication has meant to our industry and to Georgia. It changed how we manage insects, and it allowed us to grow cotton more profitably. It also gave us the opportunity to utilize integrated pest management and beneficial insects,” he says.

It's vitally important, he adds, that Georgia remain free of boll weevils. “We're all familiar with boll weevil traps. As producers, you need to make sure these traps are standing and functional, and that weevils aren't re-introduced into the state.

“It's your money that's being spent to clean up weevil infestations. And the earlier weevils are detected, the cheaper it'll be to control them. We also can do other things to help maintain our status as a weevil-free state. If you purchased used equipment from a boll weevil-infested area, make sure it's cleaned,” says Roberts.

This past year, four boll weevils were captured in Georgia — the fewest numbers ever, he says.

Boll weevil eradication, says Roberts, has offered Georgia growers many new opportunities for managing insects. “Our philosophy for controlling insects is built upon biological control and preserving beneficial insects in the field. Integrated pest management is good environmentally and economically, as we seek to maximize profits,” he says.

A look back at the number of insecticide sprays made on Georgia cotton since 1986 gives a good idea of how far producers have come, notes Roberts. Nineteen eighty-six was the last year Georgia growers had to control boll weevils, he adds, with the Boll Weevil Eradication Program kicking off in the fall of 1987.

“We had a couple of tough years during the first active part of the program, as we basically had no beneficial insects as we do today. In 1992, we considered ourselves to be boll weevil-free, and we saw a large drop in the number of insecticide sprays, down to about four to five sprays per acre. That's a big leap from six to seven years earlier, when we were spraying an average of more than 15 times.”

Another big change occurred in 1996, when Bt cotton was introduced onto the market, says Roberts, and growers saw a further reduction in the number of cotton insecticide sprays made in Georgia.

“In the past few years, we've had low insect pressure, and this past year growers sprayed an average of slightly under two applications per acre. Growers in the 1970s and 1980s could not imagine such a scenario.”

This past year, Georgia researchers conducted an insect boll damage survey to help determine which insect pests are causing the most damage to the state's cotton crop. They looked at 43 non-Bt fields and 39 Bollgard fields, collecting about 100 bolls from each field. Researchers cracked the bolls and looked for any indication of insect injury.

When all of the data was collected, researchers had looked at about 8,500 bolls and grouped them into bolls that were damaged by worms and bolls that were damaged by bugs.

“A little more than 2.5 percent of the bolls were damaged by worms and almost 3 percent were damaged by bugs. We're still losing some cotton to bugs. And even though damage is a little higher from bugs, the worm pests — corn earworms and tobacco budworms — still are the primary insect pests for us to manage. The potential for yield loss with these pests is much greater than for bugs.”

A look at the number of corn earworm and tobacco budworm sprays over time indicates a trend similar to the total number of insect sprays, says Roberts. “Once we became free of boll weevils, we were averaging a little more than three sprays per acre. The advent of Bt cotton dropped that average even more. Today, on average, we spray Bt cotton one time for worms and we spray conventional cotton two and a half times for worms.”

The survey confirms that Bt technology is “great” and has done positive things, he says. “But it is not immune to feeding by corn earworms. We know supplemental sprays are needed in some situations. If we look at the percent of boll damage on Bt cotton, it's about 1.5 percent, with a range from zero to 5 percent. On conventional cotton, the boll damage from earworms was about 4 percent.”

The goal of cotton producers, says Roberts, should not be to eliminate insect damage. “Our goal is to maximize profits. And if we maximize profits, we'll have some insect damage.”

There are many control options for managing corn earworms and tobacco budworms, he says, including pyrethroids, organophosphates and carbamates. Pyrethroids are broad spectrum, he says, having activity on many different pests. Some of the newer technologies on the market, such as Tracer, Steward and Bollgard, tend to be more selective in nature, says Roberts.

“These more selective products allow us to manage beneficial insects. And some of the even newer products, such as Denim and the new generation of Bollgard, also will be selective. We need to utilize all of our control options and tools to ultimately maximize profits.”

When evaluating options for controlling tobacco budworms, growers need to think about resistance and resistance management, says Roberts. In 1997, pyrethroid resistance in Georgia was first detected in Decatur County.

“In some areas of southwest Georgia, growers realize they have a problem with difficult-to-control tobacco budworms, and they use pyrethroids. In other areas of the state, problems haven't been as bad, but there is the potential for resistant tobacco budworms.

“We've already been doing things to manage or delay resistance. No one makes recreational sprays. We spray only when needed, and we use natural enemies. So, we're reducing selective pressure because we don't use a lot of insecticides.”

“When we have to use foliar products for tobacco budworms, we need to try and rotate these insecticides. We need to reduce the selective pressure from one particular chemistry, whether it's Tracer, Steward or a pyrethroid, and prolong the use of these products.”

It's important, he says, that growers follow the refuge requirements of Bt cotton to help preserve the value of the technology.

Bug management, says Roberts, is going to become more important in Georgia cotton. “We're talking primarily about bug management during mid to late season. These are bugs that feed on small, developing bolls. There's a complex of bugs that'll feed on these bolls, and stink bug is the primary one. Tarnished plant bugs can do the same type of damage.”

No estimate was made on stink bug damage in Georgia, he says, until 1993. This past year, about 0.8 applications per acre were targeted towards stink bugs. “Bugs are a problem, but we've come a long way in scouting and in developing thresholds.”

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