Cooperative Extension at Highmoor Farm

Spotted Wing Drosophila Alert — August 29, 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 all sites this week. Some of the increase may be due to growers no longer spraying because they have finished harvest of summer crops for the season, and the resulting increase of over ripe fruit in the field (see table below). We expect populations to increase further as more food becomes available, and we see easing of the present drought conditions. Growers with late ripening fruit, such as fall fruiting raspberries, late ripening blueberries and day neutral strawberries, should monitor their plantings closely for flies and regularly check fruit for larvae. A 5 to 7-day spray schedule on ripening fruit may be required to keep it 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.

White grubs are the larvae of several species of scarab beetles, including June beetles, rose chafers, Japanese beetles, Asiatic garden beetles and European chafers. Several of these species have been prevalent this year, so we may expect grub problems to be more common next spring and summer. The beetles lay their eggs in June and July and the grubs feed on the roots of strawberries, turf and other perennials from July through mid-September. Affected plants will be stunted and wilted and may die during dry periods. Pulling up plants reveals that roots have been chewed off about an inch below the soil line. Sifting through the soil below the plants may reveal the whitish crescent-shaped grubs which can range in size from 3/8 inch to almost 1 ½ inches long, with six legs near the head and a swollen rear-end. The two most effective periods to treat plantings for grubs are in the spring prior to when they pupate (May) and in the late summer when the next generation is actively feeding, i.e. now (late August). Materials should be applied with plenty of water to be sure they reach the root zone. Materials currently registered for control of grubs in strawberries include Platinum® and Admire Pro®. Parasitic nematodes can also provide control of grubs and should be applied with similar timing. Nematodes are very sensitive to ultraviolet light and dehydration and must be applied with lots of water. Given the abnormally dry soil conditions this year, it may not be a good option. See the New England Small Fruit Management Guide for sources of parasitic nematodes.

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

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