Spotted Wing Drosophila Update – August 12, 2022

Spotted Wing Drosophila on Raspberry
SWD on Raspberry; photo by David Handley.

Spotted Wing Drosophila Alert:  8/12/2022

David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Phil Fanning, Assistant Professor of Agricultural Entomology

Fly counts rose significantly at most, but not all, locations this week, perhaps signaling the start of the expected exponential growth of fly numbers we typically see at this point in the season.  Sites over the six-fly threshold that is considered potentially damaging to ripening berry crops included Wells, Limerick, New Gloucester, Bowdoinham, Monmouth, and Wayne. Growers should expect larvae to start appearing in the fruit unless protective sprays are applied (see table below).

Spotted wing drosophila build rapidly, and with trap counts showing a 3 to 10-fold increase this week, populations are expected to continue to rise. Protective sprays should be applied on any ripening fruit, and growers should maintain a 5-7-day spray schedule once fly numbers have exceeded the threshold or larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

Spotted Wing Drosophila Maggot in Raspberry
Spotted Wing Drosophila Maggot in Raspberry; photo by David Handley

Keep berry fields clean of over-ripe and rotten fruit as much as possible.  Rotten fruit on the plants or on the ground will greatly increase the number of fruit flies present, by providing them with food and egg-laying sites.

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


Other IPM Web Pages
Michigan State University:

Penn State University:


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.



Town Spotted Wing  Drosophila weekly trap catch 7/28/22 Spotted Wing  Drosophila weekly trap catch 8/5/22 Spotted Wing  Drosophila weekly trap catch 8/12/22
Wells 10 3 13
Springvale 5 0 5
Limerick 9 2 11
New Gloucester 37 47 84
Bowdoinham 315 259 574
Mechanic Falls 0 0 0
Monmouth 11 12 23
Fayette 2 1 3
Wayne 4 2 6