Summertime spotted wing drosophila woes

Elisabeth HodgdonCornell Cooperative Extension

 

One of our weekly tasks at the office is checking insect traps in raspberry and blueberry patches for a small invasive fly called spotted wing drosophila (SWD, Drosophila suzukii).

The fly usually shows up in early July, and we are expecting it any time now.

EGGS IN FRUIT

 

A relative of the common fruit fly, SWD has been wreaking havoc in the fruit industry in the U.S. for a decade now because growers have few options for controlling it.

As the name implies, males have a distinctive dark spot on their wings. What makes this pest particularly destructive is that females have a jagged ovipositor that enables them to pierce and lay eggs into fruit still on the bush, while most other fruit flies prefer rotting fruit.

The result is blueberries, raspberries, grapes, and other soft fruit with maggots. An unappetizing sight, without a doubt.

A CHALLENGING DILEMMA

This year, with our unseasonably cool spring, the New York strawberry crop is ripening later than usual, which may coincide with SWD’s appearance.

With the demand for organic and no-spray fruit continually climbing, fruit growers are faced with a challenging dilemma: Do they opt to maintain intensive weekly insecticide spray schedules to produce an aesthetically perfect and marketable crop, or forgo pesticides in hopes that consumers will tolerate insects in their fruit?

Spending more time spraying crops is burdensome and expensive for growers. Insecticides available for certified-organic production are not reliably effective, and resistance to the chemicals has already been documented.

Consumer tolerance for larvae in fruit is, understandably, usually zero. Growers do their best to apply as few pesticides as they can using information about the fly’s population on the farm while making sure that they can deliver quality produce to the consumer.

NOTHING BUT NET

What’s a commercial fruit grower or home gardener to do?

In recent years, small-scale growers in the Northeast have started using fine mesh netting to keep out the flies.

Although somewhat expensive, the netting allows for a spray-free berry crop while keeping the flies out.

The netting, installed after pollination is complete, must have very small holes and be secured to the ground completely around the berries.

THE BIG CHILL

For growers who prefer not to spray or use netting, cleaning off all damaged or overripe fruit and properly handling berries post-harvest can help.

If berries are refrigerated, frozen, or processed immediately after harvest, eggs within the fruit do not hatch and can die.

Sometimes, customers and backyard gardeners are OK doing this as a tradeoff for spray-free or low-input berries.

With an understanding of the fly’s habits and changes to our own, we can learn to live with SWD and enjoy the sweet fruits that summer has to offer.

Elisabeth Hodgdon is the regional vegetable specialist with Cornell Cooperative Extension – Clinton County. Reach her at eh528@cornell.edu or 518-561-7450.

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