Spotted Wing Drosophila Alert — July 7, 2026
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 flies are now being caught in traps we have set up in strawberry and raspberry fields in southern Maine (see table below). Drosophila larvae have been observed in late ripening strawberry fruit in southern Maine. This is a relatively early appearance of spotted wing drosophila in damaging numbers. This insect can successfully survive the winters here in Maine, but the overwintering population usually doesn’t build up to injurious levels until later in the summer. The presence of flies in the field at this time indicates that this pest is now actively laying eggs in developing berries. This compliments reports from other Northeastern states indicating that SWD is now active, and that numbers are increasing early this season, likely encouraged by the wet, warm conditions this spring.
If you are growing raspberries, blackberries and/or blueberries, spotted wing drosophila will be laying eggs on these fruit as soon as they begin to ripen.
Spotted wing drosophila populations may build rapidly in the coming weeks as more food (fruit) becomes available for the flies, especially if weather conditions continue to be warm and wet. Now is the time to set out your own traps, if you haven’t already. Start protective sprays on any berries that have begun to ripen when more than four spotted wing drosophila flies are caught in a trap, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.
Important points for managing spotted wing drosophila include:
- Monitor for the flies with traps, and for the larvae in fruit.
- Spray regularly and often once flies or larvae have been found in the field (every 5 to 7 days).
- Harvest fruit regularly and often; do not leave any ripe/rotten fruit in the field.
- Sort fruit at harvest; do not leave any soft fruit in the container to be sold.
- Chill all fruit immediately after harvest to 36ºF (or as close as you can) for a minimum of 12 hours to slow or stop development of any eggs or larvae.
- Prune the planting, especially the lower region, to open up the canopy and create dry, light conditions.
Products that provide good control of drosophila on berry crops include spinosad (Radiant® for strawberries, Delegate® for raspberries and blueberries), Asana®, Brigade®, Danitol®, Exirel® 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. Also, it is recommended to add 4-16 oz Nu Film P®/100 gal with all materials to improve SWD efficacy and, if it rains after you spray, re-apply a pesticide material. (Read the label for any re-application restrictions of the same material.) Please check product labels for rates, post-harvest intervals and safety precautions.
A complete list of labeled spray materials for SWD can be found in the New England Small Fruit Management Guide (link will open a new page).
| Trade Name | Days to Harvest Blueberry | Days of Residual | IRAC Group |
|---|---|---|---|
| Assail® | 1 | 5 to 7 | 4A |
| Mustang Max® | 1 | 7 | 3 |
| Bifenture® – contains PFAS chemicals | 1 (3 for raspberry) | 7 | 3 |
| Brigade® – contains PFAS chemicals | 1 (3 for raspberry) | 7 | 3 |
| Danitol® | 3 | 7 | 3 |
| Delegate® | 3 (1 for raspberry) | 7 | 5 |
| Entrust® | 3 (1 for raspberry) | 3 to 5 | 5 |
| Success® | 1 (raspberry only) | 3 to 5 | 5 |
| Exirel® | 3 (1 for raspberry) | 5 to 7 | 28 |
| Imidan® | 3 (not for raspberry) | 5 to 7 | 1B |
| Verdepryn | 1 | 5 to 7 | 28 |
A Simple Monitoring Trap for Spotted Wing Drosophila:
The trap body is made from a 16-ounce red plastic cup (we use Solo Brand P16RLR). You’ll need one that has a tight-fitting lid (we use Solo Brand 626TS). Using a 1/8” hole punch (available through art suppliers), punch about 15 holes in a row around the cup just under the lip about 1/2” apart. Leave about 2” of the diameter of the rim with no holes so that liquid can be poured in and out. Punch a second row of holes just under the first row, to give you a total of 30, 1/8” holes. Use a black permanent marker to paint a 1/2” wide black strip around the cup under the rim, right over the holes you punched. To support the trap, cut a wooden tomato stake down to about 24”. Attach a 4” or larger hose clamp near the top of the stake to act as a cup holder for the trap. (We punched a hole in the metal band of the hose clamp and attached it to the stake with a flat-headed wood screw.) Place the trap holder in a shady, moist place in or near the fruit planting, with the cup height 12” to 18” off the ground. Fill the trap with 4 to 6 ounces of apple cider vinegar, + tsp. sugar + a pinch of yeast, or whatever bait you prefer. It is best to add a few drops of unscented soap to break the surface tension of the liquid. Place the lid on the cup to keep rain and critters from getting in, and place the trap in the holder. Adjust the hose clamp so that the trap fits in snugly but the trap holes are not covered up. Empty and re-bait the trap every week. Do not pour out the old bait on the ground near the trap, as this will draw flies away from it. Check the traps and change the bait at least weekly.
An effective commercial trap and bait is available from Scentry and can be purchased from Great Lakes IPM Company (link will open a new browser).
For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit UMaine Highmoor Farm’s Spotted Wing Drosophila Alerts webpage.
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 7/7/2026 |
|---|---|
| Wells | 9 |
| New Gloucester | 2 |
| Cape Elizabeth | 3 |
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.
University of Maine Cooperative Extension is an equal opportunity institution and provider committed to nondiscrimination. For more information, visit extension.umaine.edu/nondiscrimination.