Although the spotted wing drosophila is now established throughout Florida, the good news is it has yet to cause economic crop damage.
Nevertheless, growers of small fruit should monitor for the pest when they have a crop to determine if it has made inroads and has begun to infest the crop. “Just stay aware, know when it’s there and be prepared to react,” says Jim Price, an entomologist at the University of Florida’s Gulf Coast Research and Education Center in Balm.
In addition, growers should learn to identify the spotted wing drosophila and how to differentiate it from the common but smaller Drosophila melanogaster that is found around rotting fruit, says Oscar Liburd, a UF associate entomology professor in Gainesville.
The good news, Liburd says, is the new pest can be controlled with an integrated program of monitoring, field sanitation and pesticides, if needed.
The spotted wing drosophila, a native of Japan, China and India, was first confirmed in the United States in California in 2008. Since then, it has spread and has been found in Kentucky, Michigan, Louisiana, Utah, South Carolina, North Carolina, Washington, Oregon and British Columbia.
The first specimens were trapped in Florida in August 2009 in Hillsborough County, and SWD has become established throughout much of the peninsula, Price says.
In Florida, the SWD could potentially infest strawberries, blackberries, raspberries, blueberries and stone fruit. Liburd says there’s a question about whether it also could potentially infest grapes and tomatoes.
The state’s growers have gone through two strawberry seasons and one blueberry season without economic damage, Price says.
Blueberry growers are entering their second season since the pest was first confirmed.
Affinity for ripening fruit
Unlike the common fruit fly that lays its eggs in rotting fruit, SWD prefers fruit just reaching maturity. Using a serrated ovipositor, the female cuts through the skin of fruit to lay eggs.
The opening also provides an entry way for rot-causing pathogens.
An average female can lay 300 to 400 eggs, Liburd says.
As the larvae develop, they eat the flesh, rendering the fruit unmarketable.
SWD is most active when temperatures average 68 to 69 degrees Fahrenheit, and adult activity falls off significantly when temperatures top 86 degrees.
“This might be good for Florida because I know in April and May the temperatures are much higher than that,” he says.
Based on trapping conducted between August 2009 and September 2010, Liburd says peak populations occurred in December and January. In 2010, another peak occurred in June and July.
Growers can monitor for the pest by making simple traps from 32-ounce plastic containers with lids.
Drill four 3/8-inch holes around the top of each container, and fill them with about 1 ½ inches of a fermented bait solution made from ½ packet of baker’s yeast (found in the grocery store baking aisle), 4 tablespoons sugar, 12 ounces water and two drops surfactant or unscented dish detergent.
Entomologists in Oregon recommend using apple cider vinegar in traps.
But Price says his research has found the yeast-sugar mixture to be more effective under Florida conditions, and he’s given up on the vinegar.
To make the traps even more attractive, Liburd recommends placing a band of yellow paper or cardboard around the inside of the cup above the waterline.
Drill two small holes near the top and attach a hanging wire.
In blueberries, Liburd recommends placing them at a rate of two per acre, with one on the exterior and one in the interior of the field. Position the traps inside bushes.
For strawberries, Price recommends hanging one trap on each exterior side of the field to keep them away from tractor activity. Check the traps and replace the yeastsugar solution at least weekly.
Field sanitation also will be a key component since rotting fruit can attract SWD, Liburd says. “Harvest ripe berries on a regular basis, and remove all dropped berries,” he says. “Sanitation is extremely important.”
Controlling SWD will be more successful on an area-wide basis, Liburd says. If you’re vigilant about trapping and culled fruit removal and your neighbor isn’t, the pest could build up next door and move into your field.
Price says there is no economic treatment threshold, since the fly has yet to cause economic damage.
If needed, several products will control the pest, including Delegate, Phosmet, malathion, diazinon, Danitol, Mustang and Asana. In selecting a product, growers should take into account pre-harvest intervals, which can run as high as 14 days, Liburd says.
Growers also should consider a pesticide’s impact on beneficial insects, such as bigeyed bugs and minute pirate bugs, Liburd says. For organic producers, GF120, Pyganic, Entrust and Aza-Direct will provide some level of control, he says.
Kaolin clay, which prevents the females from ovipositing on fruit, also is an option. But the product leaves a white film that could affect marketability if it isn’t washed off the fruit, he says.
For more information, download the UF EDIS publication, http://edis.ifas.ufl.edu/in839.