The spotted wing drosophila – Minnesota’s newest fruit pest

I have taken some pride over the years that when asked a garden question I may not know the answer to, I usually know someone who does. That all changed when the spotted wing drosophila, aka SWD fruit fly, became a menacing problem in our Chisago County area. This is one frustrating insect and making it more so is that no one seems to have the answer to how to control or eradicate it.
The SWD is native to Asia and was first found in California in 2008. It has been moving toward the Midwest and in 2012 was confirmed in Ramsey, Hennepin, Anoka and Olmsted counties. To date, the primary crop being attacked are raspberries, but grapes and wild blackberries were also found to be affected.
Unlike the common fruit flies that attach our overripe bananas, the SWD feeds on healthy, intact, ripening fruit. It mainly attacks the thin, soft fruits, like raspberries, blackberries, blueberries, strawberries, grapes, plums and cherries. Up until this year it wasn’t a problem until we had the heat and weather of late summer; therefore strawberries and blueberries weren’t affected.
The female uses a saw-like egg laying structure to lay their eggs in the ripening fruit. It is possible that larval feeding won’t show until after the crops has been harvested and sometimes not until the fruits are in possession of the consumer.
I received a call from a Chisago County gardener two weeks ago saying that a neighbor was invited to pick in her patch. A couple of days later the neighbor called and said that the berries were crawling with whitish maggot-like worms – that’s the SWD. She called the U of M and they told her that while no one wanted the infected berries, the unaffected berries were OK.
My ever bearing raspberries are just beginning, so in one patch I picked some of the old berries and put them in a recycled container and put them aside for four days. When I opened the container, sure enough, those worms were crawling up the side. I did notify the U of M.
I have questions but no one seems to have answers. I asked about chemical control, since some chemicals are harmful to bees and I do have bees around. What kind? How much? How often? What are commercial growers doing to protect their berry crops?
The Almelund Threshing Show will be held Friday through Sunday, Aug. 7-9. Another good reason to visit the Master Gardeners there in our pioneer building is to get more information about SWD. Peggy Boike, Chisago County Master Gardener, has put together some very good displays that include the SWD. We are located at the east end of the Threshing grounds next to the Barber Shop and behind the Old Court House Building.

Leave a Reply

Your email address will not be published. Required fields are marked *