"We need a bait that attracts flies before they get to the fruit," Sial says. Ripe fruit emits more complex odors that will always beat out current trap baits.
A pheromone attractant would be the ideal lure, but isn't yet available, he says.
Trap design and color appear to make little difference in their effectiveness. It's all about the bait, Liburd says.
Yeast-based baits tend to work best, but must be renewed at least weekly. At seven days, decomposing yeast attracts a wider range of insects, making it harder to identify spotted wing drosophila. And after 10 days, he says, the pest begins to reproduce in the bait.
Apple cider vinegar is the next-best bait, he says.
Liburd recommends lidded plastic cups as traps. With wire hangers and pinholes that allow fly access, they cost less than $1 each.
The most effective pesticide controls now are pyrethroids, spinosyns and organophosphates. Rotating among the different classes from week to week is critical for resistance management, the researchers say.
"No one tool will last the entire picking season," Burrack says. Growers must take into account environmental conditions, preharvest intervals and residue tolerances.
That often means balancing tradeoffs. Mustang Max [zeta-cypermethrin] has a one-day preharvest interval but isn't accepted by some export customers. Malathion has a short preharvest interval and fewer export issues, but isn't as effective under rainy conditions. And Delegate [spinetoram] offers excellent results with longer residual effects—but isn't available to organic growers.
Entrust (spinosad), one of two effective options for organic growers, is limited to six applications per season, Sial says.
Other possibilities include Hero [zeta-cypermethrin and bifenthrin] and, still awaiting registration, both cyazypyr T and sulfoxaflor, Liburd says.
Given spotted wing drosophila's wide host range and strong flying abilities, growers should keep watch outside their field borders. Liburd says early-season perimeter sprays may provide more value, but that theory requires further study.
Attacking nearby wild hosts—especially wild blackberries—will reduce overall populations, he says, suggesting a 10-foot buffer.
An organic approach
Donna Miller, owner of the certified organic D&J Blueberry Farms in Inverness, Fla., relies on both Entrust and PyGanic [pyrethrin], especially for border areas in fields surrounded by woods. She monitors traps daily, most placed in field perimeters to guard against incoming flies.