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Spotted Wing Drosophila Update: August 10, 2015

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

Spotted Wing Drosophila Maggot in Raspberry

SWD Maggot in Raspberry, photo by David Handley

Spotted wing drosophila captures are becoming more widespread this week, although numbers are still quite low at most sites. The highest numbers of flies were caught in traps in Buxton (21) and Livermore Falls (19). Single female flies were caught in traps in Wells and Oxford; and two flies were caught in traps in Limington, Limerick and Springvale. According to recent research in wild blueberry fields by Frank Drummond at the University of Maine, spotted wing drosophila becomes a serious threat when 6-10 or more flies are caught in a yeast-baited trap in a week. This suggests that flies are now a threat in some locations in Maine and any berry fields where flies have been caught with ripe or near ripe fruit should be protected.

Spotted wing drosophila populations are likely to increase 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 are caught in traps, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

Spotted Wing Drosophila Trap with One Male SWD Circled

Spotted Wing Drosophila Trap, Male SWD Circled, photo by Kaytlin Woodman

Last year, populations did not reach damaging levels until September; but weather conditions can alter how quickly the flies will build up. Frequently repeated insecticide sprays (1 to 2 times per week) are often needed to prevent infestations once the insect is present in a field. Products that provide good control of drosophila on berries 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:

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

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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