Fly pest can gain the upper hand without vigilance

02/06/2014 02:01:00 PM
Renee Stern

spotted wing drosophila trapHannah Burrack, North Carolina State UniversityYou can make an inexpensive spotted wing drosophila trap using a drink cup with a lid and bait of sugar and yeast. For more information, visit North Carolina State University.Buyers' zero tolerance for spotted wing drosophila is pushing Southeastern blueberry growers to extra vigilance against the prolific and nimble pest.

With no natural enemies currently available to keep the fly in check, growers have few tools other than frequent pesticide applications. Spotted wing drosophila reproduces rapidly; each female can lay up to 600 eggs and a single season can see up to 16 generations.

"It's a multiplying fool," says Joe Cornelius Jr., chairman of the Georgia Blueberry Commission and president of J&B Blueberry Farms in Manor. "It can get real bad in a hurry."

The development of pesticide resistance is "a major fear," Cornelius says.

The region's blueberry crop loss in 2012 topped $23 million.

Cornelius' 2012 crop was devastated after extensive rain—20 days out of 22—upended his spray program. "We left a lot of fruit in the field in 2012," he says. Last year was also rainy but broken up by a few hot, dry days that kept spraying on track.

"It's a risky proposition to have even a potential infestation," says Hannah Burrack, associate professor of entomology at North Carolina State University in Raleigh. "They go from zero to 60. You may have a few larvae one week and the next week they're everywhere."


A preventive approach

That speed underlies recommendations to take a preventive approach. Ash Sial, assistant professor of entomology at the University of Georgia in Athens, suggests growers begin pesticide sprays when berries start turning color from green.

But Oscar Liburd, professor of fruit and vegetable entomology at the University of Florida in Gainesville, urges using baited traps to gauge pesticide timing.

"Spraying every seven to 10 days isn't sustainable," Liburd says.

Spotted wing drosophila zero in on ripening fruit odors.

"In the middle of the season, the power of fruit volatiles from the field overpowers (trap lures)," he says.

"But in the beginning of the season, before the fly population gets really high, you can use traps effectively. With good monitoring I believe you can reduce the number

of sprays."

As more berries ripen, growers should also sample fruit as an extra check, Burrack says.


Traps don’t always tell the story

Trapping has proved frustrating for Cornelius. In 2011, high counts in traps didn't translate to significant numbers of the pest in his fields. The next year, when his traps caught hardly any, he lost more than 200,000 pounds of blueberries.

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