Spotted Wing Drosophila

SWDA New Pest in Town

We’ve made reference to it previously, but more and more we’re getting reports of the Spotted Wing Drosophila (SWD) being in WA state — both out east in the orchards and here in the city. It’s kind of a big deal as it’s a new pest and so there are still a lot of experiments with how to deal with it. And it’s attacking soft fruit (peaches, berries, etc.), which have previously escaped things like the Apple Maggot Fly and Coddling Moth. More and more we’re finding it necessary to undertake pest prevention methods for all kinds of fruit.

About Spotted Wing Drosophila (SWD)

The pest is originally from Asia, but has made its way up to Washington from California — it’s rapidly spreading from state-to-state. They are closely resemble the common vinegar fly but the difference is instead of attacking rotting fruit, the SWD attacks perfectly healthy fruit. It was really first seen around Japan and other parts of Asia in the 1930s. The way it works is that females search for soft fruit, land on the fruit, and then lay their eggs — laying as many as 300 eggs in their lifespan and up to 13 generations per season. The larvae then grow inside of the fruit.

University of California has this helpful resource to see photos of the life cycle of the SWD and its impact on fruit.

The economic impact could be somewhat significant for soft fruit and would vary by region. But not enough research has been done to provide an accurate estimate.

Treatment

We only recommend non-chemical ways at managing existing SWD infestations. If only some fruit is infested, the best approach is to harvest & sort the crop immediately — separating the good from the bad. And to help reduce the number of SWD in the future, we suggest placing infested fruit in a sturdy, sealed plastic bag and dispose of it in the trash. Also, be sure to remove any fruit that has fallen on the ground and any infested fruit remaining on the plants. But do not compost! This will not kill the insects.

Prevention

As this is somewhat of a new pest to the U.S., there are a lot of tests going on as to the best method to prevent SWD infestations and protect vulnerable fruit. Oregon State University has a great resource for backyard growers. The best known approaches so far….

  • Traps: There are a number of different types of traps people are trying, but below is a video for one in particular. These will not only help you capture SWDs, but also monitor how many are in your area.

  • Netting: A few places have suggested setting up netting over your soft fruit plans and trees prior to the fruit developing.
  • Habitat & Varieties: One way to prevent the SWD is by selecting thick-skinned fruit varieties that are more resistant to the pests. Also, to modify any other plants you have in your yard that might attract the SWD — thus making it less likely that they’ll find your habitat attractive.

So keep an eye out for this pest. We’ve already heard from folks about it attacking their raspberries and currants. If you find it in your backyard, definitely drop us a line (info@cityfruit.org) — we’d love to better understand how and where this infestation is happening so we can help work to manage it better.

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