Research examines Spotted Wing Drosophila

Special to The New Jersey Farmer

HAMMONTON (June 1, 2014) — When Spotted Wing Drosophila became a problem in New Jersey blueberry fields two years ago, Bobby Galletta of Atlantic Blueberry Company was ready to defend his crop from the destructive vinegar fly that lays its eggs in ripening fruit.
“We knew it was coming,” says Galletta, who manages 1,300 acres of ‘Jersey Blues’ on the family-owned farm near Hammonton. “It had already taken the West Coast by storm, and it was on its way east.”
With zero tolerance for larvae in harvested fruit, Galletta and other growers who cultivate blueberries on 7,600 acres of sandy, acidic soil in the New Jersey Pinelands cannot afford to let this pest get out of control.
With the arrival of SWD, Galletta was forced to tighten his insecticide spray schedule to control what can be up to 10 generations of SWD in a single season.
“We spray by the calendar every seven days,” he said.
Concerned about the economic damage this pest can inflict, Galletta and other blueberry growers in the Hammonton area are adhering to recommendations by Rutgers University’s Cooperative Extension that they treat for this pest every seven days after their fruit begins to color.
With a limited number of insecticides available, there is also concern that repeated use of any one class of insecticides will lead to resistance development and render that insecticide useless against SWD.
“There are only five classes of insecticides that work well against SWD,” according to Cesar Rodriguez-Saona, an entomologist with Rutgers University’s Philip E. Marucci Center for Blueberry and Cranberry Research and Extension in Chatsworth. “So, we are recommending that growers rotate insecticides with different modes of action in their spray schedule so that the insect does not develop resistance to any one class of insecticide.”
While some of these insecticide classes are highly effective against SWD, they can also eliminate natural predators that keep secondary pests under control.
“Researchers and growers are concerned that repeated use of certain insecticides will cause problems with other pests such as aphids, scale insects, and leaf miners,” says Rodriguez-Saona.
However, ongoing research by Rodriguez-Saona is identifying some insecticides that are highly effective against SWD while maintaining healthy populations of beneficial insects.
In trials conducted at the Marucci Center over the last two years, Delegate insecticide, a green chemistry from Dow AgroSciences, demonstrated excellent control of SWD, giving growers another tool in their battle against this invasive pest.
“Delegate works very well against SWD,” Rodriguez-Saona said. “It is highly effective against the adults and also decreases the number of larvae in the fruit.”
Delegate also provides growers with a different class of insecticide to include in their spray rotation, reducing the risk of resistance.
“Reduced-risk insecticides like Delegate are more target-specific to insect pests,” says Rodriguez-Saona. “They are less harmful to natural enemies of secondary pests, so they are more compatible with IPM practices such as biological control.”
“Delegate is an optimum rotation partner,” says Rodriguez-Saona.  “There has been an increase in the use of Delegate since SWD was found here.
“The growers are using it. They know it works.”
As part of his research, Rodriguez-Saona is looking into more effective baits for monitoring SWD infestations so growers will have a better idea of when their fruit is at risk.
“The baits that we use now do not give us a good correlation between the number of flies we find on the baits and the amount of infested fruit we have in the bushes.”
Rodriguez is optimistic that one of the lures now under development will give growers a more accurate gauge for predicting an infestation.
“The lure contains volatiles emitted by vinegar and wine that attracts SWD,” he said. “We tested it last year, and it worked. So, we are hoping it will be commercially available soon.”