Two insect control systems considered

In this final 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.

Any discussion of cotton insects in today's farming environment must take into account two very different systems, says Ron Smith, Auburn University Extension entomologist.

“The system a grower experiences will be determined whenever he purchases seed,” says Smith. “And, in reality, most growers have some of both systems, because we're talking about Bollgard and conventional cotton varieties.”

The primary target pest in the conventional system, he says, likely will be worms — bollworms and tobacco budworms. “The question we must answer is which pest we're dealing with at any given time. If we're dealing with bollworms, then the chemical choice is pyrethroids, which also control plant bugs, fleahoppers, stink bugs and severely suppressed beneficial insects. The cost would be about $3.50 to $5 per acre application.

“If the problem is budworms, then we'd want to use one of the newer chemistries, such as Tracer, Steward or Denim. The cost will be between $9 and $14 per acre application, and no control will be achieved on plant bugs, fleahoppers or stink bugs. Furthermore, these insecticides will leave most all beneficials in the field to work on future worms,” says Smith.

Growers don't always know, he adds, if they're dealing with bollworms or budworms, and they can't afford to guess and be wrong.

“If we go with the less expensive pyrethroids first, and wait several days for results, it's too late to use the more effective and more expensive chemistry. Growers with conventional acreage had better hope that this multi-year trend of no worms continues, and that we never get back into even economic levels of worms”

For the conventional system in 2002, Smith suggest that growers be hesitant about spraying plant bugs seven to 10 days prior to or during a moth flight.

“I would depend on beneficials for worm suppression until about July 15. If controls are necessary before that time, then the 1.5 ounce rate of Tracer — with a cost of about $9 — is an effective treatment.

“In this system, both plant bugs and stink bugs should be controlled as necessary between July 15 and cotton maturity. If pyrethroids are needed for bollworms during the late July-early August window, then stink bugs should be less of a problem since pyrethroids do an adequate job of controlling them.”

With the Bollgard system, growers should anticipate a lower spray environment, says Smith. The primary target pest, he adds, likely will be plant bugs and stink bugs, which can be controlled for about $3 to $4 per acre application.

“In this system, beneficials are important but not as critical. Growers can control plant bugs early and at mid-season without fear of beginning an insecticide treadmill for worms.

“Stink bugs, especially in the more southern areas of the state, will be the dominate pest from late July until maturity. As many as two to three applications may be necessary. In a given year, in sporadic fields, pests such as fall armyworms or soybean loopers could reach damaging levels.”

Since the bug complex probably will be the most dominant economic pest in the Bollgard system, scouting techniques and treatment thresholds will be important, says the entomologist.

“For plant bugs in pre-bloom cotton, we can use a pinhead square loss of 20 percent as a good trigger for treatment. After bloom, it's not as easy to determine thresholds. We suggest using 15 percent ‘dirty’ blooms, which indicates plant bug feeding on the large square just prior to blooming — and the presence of both adult and immature plant bugs in white blooms.”

Stink bug thresholds, notes Smith, are not an exact science. Observing stink bugs in field, he says, is difficult since they are shy of noise.

“Therefore, they will not be visible when walking through fields unless they are many times above treatment level. We can quickly and quietly shake them over a drop cloth. In this case, Alabama uses a threshold of one per 20 row feet.

“A better method for determining stink bug damage is to slice quarter-diameter immature bolls and look for internal injury. This injury may consist of warts or calluses on the inner boll wall, yellow stained lint or internal rot of one or more locks.”

There are pros and cons in both the Bollgard and the conventional systems of producing cotton, says Smith. “Bollgard eliminates the uncertainty of your insect control budget or either your worm damage losses. With Bollgard, we can budget one to three bug sprays for plant bugs and stink bugs — with a product such as Bidrin — and be reasonably accurate of knowing the total costs of insect control, with little or not insect losses, before the season begins.

“Bollgard does put pressure on scouts and consultants to determine thresholds for plant bugs and stink bugs, which sometimes isn't easy or clear cut. But on the other hand, it allows insect checkers to focus on one or two pests which makes them more efficient and accurate.”

Scouts cannot focus, all at the same time, on worms, plant bugs, stink bugs and other pests that may occur in conventional cotton, says Smith. In a conventional system, he says, certain pests tend to fall through the cracks and sometimes not be detected in time to prevent economic damage.

“A second point in a conventional system is that the new chemistry for budworms does not perform as well when applied by air. Higher rates may be necessary under heavy worm pressure.

“A third point is that the tobacco budworm is the only cotton pest where timing of controls is extremely critical. From the time a budworm hatches, we have a three to five-day window to detect the pest and apply effective controls. What happens in conventional cotton when a budworm outbreak coincides with a multi-day wet period or even with irrigation scheduling?”

With conventional cotton, growers are hoping for insect pressure to continue as it has in the past few years, especially in this era of depressed cotton prices, says Smith.

“Insect control costs in conventional systems have been next to nothing in the past few years, and insect damage has been very low. However, if this should ever change, one generation of budworms at damaging levels either will do as much damage as the Bollgard costs, or it will cost as much to control with newer chemistry as the Bollgard technology costs.

“Two applications, at $12 per acre application, is about all we can squeeze from a technology fee alternative. Only the grower can decide if the budworm insurance with Bollgard, and locking in insect control costs and insect damage, is worth the technology fee in 2002.”

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