Home Horticulture Pest Alert:  Spotted Wing Drosophila (SWD)

The Spotted Wing Drosophila (SWD) has very quickly become a devastating pest of berry crops in Missouri.  Adults were first detected in monitoring traps in late June, 2013.  By mid-August, infestations to fruit crops state-wide had been reported.  This invasive insect pest can attack small fruit and stone fruits:  (raspberries, blackberries, blueberries, elderberries, grapes, cherry, nectarine and peach)  Additionally, SWD can attack high tunnel tomatoes and wild host including pokeweed, autumn olive, crabapple, Amur honeysuckle and wild grapes.

SWD originated in Asia and has been in Hawaii since the 1980s.  It was detected in California in 2008 and detected in Florida, Utah, the Carolinas, Wisconsin and Michigan in 2010.  It is suspected that it arrived in Missouri earlier but was not identified until 2013.

SWD flies look similar to the small vinegar flies that are typically found around or feeding on fermenting overripe fruits and vegetables. However, SWD have serrated egg-laying ovipositor which allows them to cut a slit into the skin of healthy intact ripening fruit to lay their eggs.  Symptoms may not be visible until after the fruit is harvested.  The damage caused by the larvae makes the fruit susceptible to infestation by other insects as well as diseases of fungi and bacteria.

Because this pest is so new to Missouri, there is no local research on insecticide treatments and therefore recommendations are based on other states.  Monitoring is the key to treatment and application should be made about 2-3 weeks before berry harvest.  A second application may be needed 5-10 days after the first application depending on the residual effectiveness.  For the home-owner, Spinosad insecticide is effective and has the least negative environmental effects of currently available products.  The organophosphates (malathion is most widely used) will control SWD but are very toxic to bees and beneficial insects and should be used as a second choice.  You should also be aware of the pre-harvest interval from any insecticide used.

Lincoln University and the University of Missouri IPM programs are joining efforts to conduct a state-wide monitoring system for SWD in 2014.  Alerts will be made through the MU Pest Monitoring Network. 

Source: Todd Lorenz, Agronomy Specialist