Spotted Wing Drosophila Alert — August 22, 2025
David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Phil Fanning, Assistant Professor of Agricultural Entomology, Christina Howard, Maine New Farmers Project Manager
Spotted wing drosophila fruit fly numbers are rising at most of our trapping sites this week, although the increases are relatively moderate for this point in the season (see table below). The drought conditions much of the state is experiencing is likely slowing population growth and keeping more flies from coming into the state on storm fronts. Changes in these conditions could stimulate higher pressure rapidly. The increased pressure observed this week may require some fields to shorten intervals between sprays to keep larvae from infesting ripening fruit. A 5 to 7-day spray schedule on ripening fruit may be required to keep fruit in good, marketable condition.
If you are growing raspberries, blackberries and/or blueberries, you should be managing spotted wing drosophila on any fruit that is presently ripening and/or being harvested to prevent infestation.
For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit our SWD blog.
Drought: It’s official: most of southern and coastal Maine is presently under drought conditions. All plants that are now ripening fruit have high water demands, usually about two inches of water per week, to properly size and ripen fruit without causing lasting stress on the plants.
Irrigation is the best method to prevent and alleviate drought stress, when possible. As harvest season comes to an end for blueberries and raspberries, the plants are already beginning the process of forming flower buds for next year’s crop. Plants experiencing drought stress may produce fewer and/or weaker buds, resulting in loss of yield and quality the following spring.
Other IPM Web Pages
Michigan State University Spotted Wing Drosophila
Penn State University Spotted Wing Drosophila Overview
University of New Hampshire SWD Weekly IPM Reports
David T. Handley
Vegetable and Small Fruit Specialist
Highmoor Farm
P.O. Box 179
Monmouth, ME 04259
207.933.2100
UMaine Extension Diagnostic Research Lab
Pest Management Unit
17 Godfrey Drive
Orono, ME 04473
1.800.287.0279
| Town | SWD weekly trap catch 8/1/25 | SWD weekly trap catch 8/8/25 | SWD weekly trap catch 8/15/25 | SWD weekly trap catch 8/22/25 |
|---|---|---|---|---|
| Wells | 65 | 113 | 135 | 323 |
| Springvale | 17 | 22 | 67 | 201 |
| New Gloucester | 94 | 478 | 190 | 57 |
| Cape Elizabeth | 67 | 107 | 474* | 388* |
| Bowdoinham | 21 | 21 | 27 | 103 |
| Mechanic Falls | 0 | 14 | 86* | 115* |
| Monmouth | 37 | 145 | 40 | 24 |
*plot is no longer being sprayed
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