The first spotted wing drosophila of the 2012 season was found in a trap in Limington on Friday, July 13. Three male flies were caught in a trap in the woods adjacent to a raspberry planting. We haven’t caught flies in other locations yet, but growers should be on alert for indications of fruit flies in their plantings and premature fruit decay.
Spotted Wing Drosophila (Drosophila suzukii) is a new pest which is a concern for raspberries blueberries and day neutral strawberries, as well as many other soft fruits. This insect is a small fruit fly, similar to the type that fly around the over ripe bananas in your kitchen. However, this species will lay its eggs on fruit before it ripens, resulting in fruit that is contaminated with small white maggots just as it is ready to pick. As a result, the fruit quickly rots and has no shelf life. This insect recently came into the U.S. from northern Asia, and caused problems with many berry crops up the east coast last year. It can complete a generation in under two weeks, with each adult female laying hundreds of eggs. Therefore, millions of flies can be present soon after the introduction of just a few into a field. This makes them very difficult to control, and frequently repeated insecticide sprays (3 to 5 times per week) may be needed to prevent infestations once the insect is present in a field. It is likely that spotted winged drosophila can successfully over winter here, although it may not build up to damaging levels until summer. We have set out monitoring traps for spotted winged drosophila in fruit plantings around the state to determine the activity of this pest in Maine. However, these traps are unlikely to provide early warning, i.e. when we find them in a trap they are probably already established in the field. We will be alerting growers when we find them in Maine. Now that spotted wing drosophila has been confirmed in a berry planting southern Maine, growers should be on the alert and look for fruit flies on their fruit and symptoms of premature fruit decay. Products that provide good control of drosophila on berries include Radiantâ, Brigadeâ, Danitolâ, and malathion. Please check product labels for rates, post-harvest intervals and safety precautions. Keeping the fields clean of over-ripe and rotten fruit can also help reduce the incidence of this insect. For information on identifying spotted wing drosophila and making your own monitoring traps, visit the Michigan State University’s Spotted Wing Drosophila website at: http://www.ipm.msu.edu/swd.htm. There is also a good fact sheet on management of spotted wing drosophila from Penn State at: http://extension.psu.edu/fruit-production/news/2012/spotted-wing-drosophila-fact-sheets-completed-and-on-line.
David T. Handley, Ph.D.
Vegetable & Small Fruit Specialist
University of Maine Cooperative Extension
Highmoor Farm, P.O. Box 179
Monmouth, ME 04259-0179