Spotted wing drosophila (SWD) began showing up in traps in North Carolina strawberry fields in late April.

The threat seemed pressing enough that the Extension service recommended preventive measures, said Hannah Burrack, North Carolina Extension entomologist.

“Ripening and ripe fruit are susceptible to attack by SWD attack,” said Burrack, “but the insects do not appear to be attracted to unripe fruit.”

If adult SWD are present on your farm, aggressive management is warranted, she said. That would include the following steps:

• Do an excellent job of sanitation. Fruit should be harvested frequently and completely. “Any unmarketable fruit should be removed from the field and either frozen, ‘baked’ in clear plastic bags placed in the sun or disposed of offsite. This will either kill any larvae present or remove them from your farm.”

• Prune to maintain an open canopy. This may make plantings less attractive to SWD and will facilitate pesticide applications. Leaking drip lines should be repaired, and overhead irrigation should be minimized.

• Apply insecticide treatments at least every seven days and repeat in the event of rain. Select effective insecticides with pre-harvest intervals amenable to picking schedules, and rotate insecticide modes of action between each treatment.

But don’t exceed the maximum applications per season. Some insecticides that are effective against SWD are Brigade (bifenthrin), Radiant and Malathion. Danitol is effective but has a longer pre-harvest interval, and carbaryl longer still.

• Sample your fruit regularly. At least 100 fruit per block per harvest should be observed for infestation.

SWD had been observed only on strawberries in North Carolina in the early spring, but it can attack other berry crops. “Last year, it affected some commercial blueberries, and two seasons ago, it caused significant damage in blackberries,” Burrack said.

 

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The caneberry crops — blackberries and raspberries — are probably the most vulnerable to SWD, said Doug Pfeiffer, Virginia research and Extension entomologist.

“After that might come blueberries and cherries, followed possibly by grapes,” he said.  “Apple and pear are on the host list, but we don’t consider them to be at much risk because the skin is relatively hard.”