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Spotted Wing Drosophila Alert: July 20, 2015

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Male and Female Spotted Wing Drosophila Flies

Male (left) and Female (right) Spotted Wing Drosophila, photo by Griffin Dill. Actual size: 2-3 mm.

SPOTTED WING DROSOPHILA ALERT: JULY 20, 2015

Click on photos to enlarge.

David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist; Frank Drummond, Professor of Insect Ecology/Entomology

Spotted wing drosophila (Drosophila suzukii) is a new pest that is a concern for growers of raspberries, blueberries and day-neutral strawberries. This small fruit fly is similar to those that hover around the ripe bananas in your kitchen, but 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. Infested fruit quickly rots and has no shelf life. Spotted wing drosophila 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. Repeated insecticide sprays (1 to 2 per week) may be needed to prevent infestations once the insect is present in a field. The flies can successfully overwinter in Maine, although they may not build up to damaging levels until late summer. We have set out monitoring traps for spotted winged drosophila around the state to determine its activity in berry fields. However, these traps may not provide adequate early warning, i.e. when we find them in a trap they are probably already getting established in the field.

We have found a few spotted wing drosophila in Maine over the past week, including single flies in Buxton and Limington and two flies in a trap in Mechanic Falls. These are not yet damaging numbers. Research in Maine and other regions suggests that when 6 to 10 flies are caught in a yeast-baited trap in a week, larvae will start appearing in the fruit.

Products that provide good control of drosophila on berry crops include spinosad (Radiant® for strawberries, Delegate® for raspberries and blueberries), Brigade®, Danitol®, malathion and Assail®. Research suggests that adding table sugar to group 4A insecticides, such as Assail®, may improve their effectiveness. The recommended rate would be 1-2 lbs. sugar per 100 gallons of spray. Please check product labels for rates, post-harvest intervals and safety precautions. Keeping fields clean of overripe and rotten fruit will also help reduce the incidence of this insect.

For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit our SWD blog. Other SWD sites include:

drosophila trap

Drosophila Trap, photo by David Handley

Michigan State University’s website,
Pennsylvania State University’s SWD website, and
University of New Hampshire’s SWD web page.

Spotted wing drosophila populations may start to build rapidly in the coming weeks as more food (fruit) becomes available for the flies, especially if conditions remain warm and humid. Now is the time to set out traps, if you haven’t already. Start protective sprays on any berries that have begun to ripen, once more than 4 spotted wing drosophila flies are caught in a trap, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                       Pest Management Office
P.O. Box 179                             491 College Avenue
Monmouth, ME 04259          Orono, ME 04473
207.933.2100                           1.800.287.0279

Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

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