Drosophila Trap
Drosophila Trap, photo by David Handley

David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Christina Howard, Produce Safety Professional

Click on photos to enlarge

Spotted wing drosophila (SWD) fruit fly numbers increased at nearly all of our monitoring sites this week, and we should expect higher numbers next week because the recent tropical storm probably brought up more flies from southern regions.  Trap counts are well above levels considered damaging to ripening berry crops, especially raspberries and blueberries. Fall crops of day-neutral strawberries are also susceptible  (see table below). Sites capturing more than four SWD flies in a week should remain on a protective spray schedule to prevent fruit from becoming infested with larvae. A seven-day spray interval may still be adequate at most sites, but it is likely that a five day interval may become necessary soon, given the higher populations now present.

Spotted Wing Drosophila Larvain in Raspberry
SWD Larvae in Raspberry, photo by David Handley

Remember that keeping the field free of waste fruit can significantly reduce drosophila numbers. All fruit should be chilled to 34 degrees F (or as close as possible) immediately after harvest to halt development of any eggs or larvae.   If larvae are noticed in the fruit despite a 7-day spray schedule, a 5 day spray schedule is recommended. Look for fruit flies hovering around fruit and symptoms of premature fruit decay. The flies are most prevalent in the lower, shaded parts of the plants.


Spotted Wing Drosophila Larvae in Blueberry
Spotted Wing Drosophila Larvae in Blueberry; photo by David Handley

Be sure to read and follow all pesticide product labels carefully, especially in regards to days to harvest restrictions and the number of applications allowed per growing season. Rotate products used regularly to prevent the possible development of resistance. Current information on registered pesticides for managing SWD is available in the New England Small Fruit Management Guide.  The online version is free and can be viewed here

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


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University of New Hampshire


David T. Handley
Vegetable and Small Fruit Specialist


Highmoor Farm                      Pest Management Unit
P.O. Box 179                            17 Godfrey Drive
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.


Spotted Wing Drosophila Weekly Trap Captures in Yeast/Vinegar traps

Town Spotted Wing  Drosophila weekly trap catch 7/24/20 Spotted Wing  Drosophila weekly trap catch 7/31/20 Spotted Wing  Drosophila weekly trap catch 8/7/20
Wells 21 3 4
Sanford 2 40 135
Limington 8 115 893
Limerick 24 21
Cape Elizabeth 1 121 31
Bowdoinham 371 750 1021
Mechanic Falls 0 0 11
Monmouth 15 100 61
Wayne 13 36 661