The tiny invasive flies that brought strawberry season to an early end on some southern and central Maine farms spared Bangor-area growers, but they remain a risk to the rest of the summer berries ripening across the state, including blueberries.
The flies did their damage a month and a half earlier than usual this year, likely due to a milder winter and warm wet spring, experts said in a late June alert. Spotted wing drosophila have historically caused serious issues for blueberry growers nationally, and as the summer goes on, they will pose a risk to Maine’s blackberry and raspberry crops as well as home gardens.
Similar to the tiny household flies found on overripe fruit, this fly is actually an invasive species native to Asia, present in Maine since 2011. The flies are uniquely problematic for growers because they lay eggs in fresh, healthy berries, not just rotten or damaged ones.
The flies deposit hundreds of eggs into soft-skinned fruits like strawberries using a sawlike tube-shaped organ called an ovipositor. In two weeks or less, eggs hatch into maggots that eat through the fruit.
“When you as a farmer go to pick your fruit, even though it’s barely ripe, it is turning to goo. The reason it has turned to goo is because the larvae in there have started to hatch and are feasting on the fruit,” David Handley, a vegetable and small fruit specialist at the University of Maine Cooperative Extension, told the BDN in 2017. “Your fruit starts to melt away from the inside out.”
The flies were reported in southern and central Maine strawberries from Cape Elizabeth to Lewiston at the end of June. A recent alert from pest management specialists at the University of Maine called the development a very early appearance of the fly in damaging numbers.
Strawberries constitute a much smaller industry in Maine than blueberries; the 2022 national agricultural census recorded 66 strawberry farms on more than 7,000 acres bringing in nearly $13 million in crop sales. But they are a popular U-pick activity and mark the start of the berry season.
Blueberries brought in $55.5 million directly in 2022, according to the U.S. Department of Agriculture. Maine produces almost all of the wild blueberries sold in the country.
In past years, the fly population didn’t start to cause significant losses until the middle or end of August. Eastern and northern Maine are mostly unscathed so far, but the flies are a familiar problem for later-season crops.
At Homewood Farm in Blue Hill, strawberry season is drawing to a close without pest problems, according to co-owner Trudy Beardsworth.
“We haven’t seen a fruit fly, thank goodness,” she said.
It was a good season overall, Beardsworth said. Their biggest challenge was finding labor, a widespread issue for farm employers.
Though the flies didn’t bother their strawberries, blueberry season is about to begin for the Beardsworths, and they’ve been spraying for the fruit flies for years. If they didn’t, they’d lose the crop, Trudy Beardsworth said.
Spotted wing drosophila flies have caused such damage in blueberry fields that U.S. Sen. Susan Collins and representatives from other blueberry-producing states have twice pushed the U.S. Department of Agriculture to create a task force through the upcoming Farm Bill. The proposal has remained in committee for months.
The senator’s office estimates the fly causes hundreds of millions of dollars in economic loss each year across the country, and has increased pesticide use.
That bill sets federal priorities and funding for agriculture every five to six years. The initial proposal for the task force would allocate $6.5 million each year for five years to research and combat the fly.
One of the organic control options it would fund is the introduction of a small wasp, Ganaspis brasiliensis, to feed on the flies. University of Maine professor Philip Fanning is researching the wasp’s use with a three-year USDA grant running through next summer.
Other non-chemical management recommendations from the university extension include harvesting often and avoiding leaving rotten fruit behind in the field, storing the berries at 36 degrees Fahrenheit for 12 hours after harvest to slow larvae development and pruning around the base of plants to increase airflow.
