One of the bigger garden questions last year was whether we would see spotted wing Drosophila (SWD) again in 2013. SWD flies are invasive insect pests that damage a variety of thin-skinned fruit crops, such as raspberries, blackberries, strawberries, cherries, plums, blueberries, and grapes.
Photo 1: Female spotted wing Drosophila on blackberry. It lacks the dark spot on its wings that males have.
Unfortunately the answer is yes. The University of Minnesota and Minnesota Department of Agriculture (MDA) have detected and confirmed the presence of SWD in Minnesota this year. The fire confirmed report of SWD this year occurred on June 27 when a male SWD was found in a vineyard in Dakota County. SWD was then verified on July 3 in summer raspberries in Rice County. There have also been fly specimens suspected to be SWD in several other counties not only in the Twin Cities area, but also in Greater Minnesota. You can go to the MDA website to check for updated information on where SWD has been found. Last year, the first SWD was found in August. Eventually, SWD was confirmed in 29 counties in Minnesota.
SWD looks very similar to the small fruit flies you might see flying around overripe fruit on your kitchen counter. They are about 1/8th inch long, yellowish brown with red eyes. The male is fairly easy to identify; look for a dark spot near the tip of the wing. Unfortunately, the female lacks this spot and is difficult to identify without high magnification. The larvae are cylindrical in shape, tapering at one end. They are legless, whitish and very small, no more than 1/8 inch long. However, if you find fruit fly adults or larvae associated with healthy fruit, there is a good chance it is SWD; other fruit flies are typically associated with overripe and rotting fruit.
If you have potentially susceptible fruit in your garden, consider putting out vinegar traps to try to detect SWD so you have some warning if they are present in your garden. If you do find SWD, be sure to harvest ripe fruit frequently. Remove and dispose of any overripe or rotting fruits. You can also use insecticides to help protect your fruit. Target the adults though, as there is not any practical solution one fruit is infested by the larvae. The only option is to properly destroy the fruit so the flies cannot finish their development.
For more information on SWD management, see the publication Spotted wing Drosophila in home gardens.
If you believe you have SWD, especially in a county where it has not been confirmed, contact the Minnesota Department of Agriculture "Arrest the Pest" hotline by email at firstname.lastname@example.org or leave a voicemail at 1-888-545-6684.