Spotted Wing Drosophila Update – September 30, 2022

Female Spotted Wing Drosophila
Female Spotted Wing Drosophila; photo by Christina Howard

David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Phil Fanning, Assistant Professor of Agricultural Entomology, Christina Howard, New Farmers Program Manager

Spotted wing drosophila fly counts have dropped at all sites this week, but the numbers are still high enough to pose a threat to any late ripening fruit. In past years of monitoring this pest, trap counts have been much higher at this point in the season and rising.  Why the populations are lower this year is unclear.  It has not been cold enough to deter them, and recent rains would typically encourage population growth.  Perhaps the early season drought conditions kept populations low enough to stop them from reaching the point of exponential growth that we have seen in the past.  It is still possible that fly numbers could increase in the coming weeks if food remains readily available and the weather conditions are favorable.

A 5-7-day spray schedule is recommended on all soft-fruited crops, including fall raspberries, blackberries, and day-neutral strawberries, to prevent infestation by spotted wing drosophila larvae. Sprays should continue as long as flies are present and there is still fruit to harvest.

Polana raspberriesRemoving rotten fruit from the field has been shown to significantly reduce drosophila numbers, so keep waste fruit off the ground as much as possible to reduce food and egg-laying sites.


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


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Town SWD weekly trap catch 9/9/22 SWD weekly trap catch 9/16/22 SWD weekly trap catch 9/23/22 SWD weekly trap catch 9/30/22
Wells 1184 270 214 44
Limerick 202 34 13 7
New Gloucester 577 331 227 29
Bowdoinham 86 224 292 74
Mechanic Falls 992 623 1,208 108
Monmouth* 1032 3,088 1,320 790
Wayne 832 622 721 77

Weekly spotted wing drosophila trap captures.

*Unsprayed plot