Spotted Wing Drosophila

The Spotted Wing Drosophila (SWD). Adult flies are small (2-3 mm) with red eyes. SWD male flies have a black spot on the tip of each wing and two leg bands on each front leg. The female has a large serrated ovipositor that can penetrate soft-skinned fruit, such as berries and stone fruit. She can lay up to three eggs and she, or another female SWD may revisit the same fruit multiple times to lay eggs. The eggs soon hatch into larvae (small white maggots) that feed inside the fruit, causing the flesh of the fruit to soften and discolor. The fruit surface will show depressions that leak fluids. After maturing, the larvae pupate for a varied period of time before reaching adulthood. Like other vinegar flies, SWD has a short life cycle that, depending on temperature, can be one or several weeks.

SWD has rapidly emerged as a threat to Northwest berry crops appearing in the western counties of Oregon and Washington, and western British Columbia in the later part of the 2009 season, causing economic damage to late season caneberries and blueberries. In 2010, scouting and research intensified, with results that point toward infestation beginning to climb in July-August, with later season fruit being most susceptible to damage by SWD. However, the 2010 spring was unusually cool and wet, which may have reduced SWD populations during the late spring months.

Peerbolt Crop Management Videos

• Changing a SWD apple cider vinegar trap in the field

Resources:

• Peerbolt Crop Management SWD site
• Oregon State University SWD site
• British Columbia Ministry of Agriculture and Lands SWD site
• Washington State University Mt. Vernon SWD site
• UC Online IPM

Information about construction, location, changing SWD adult traps, and about testing for SWD larvae.

1. Put out vinegar traps as soon as fruit starts coloring to determine presence of SWD in the field.  Around this time, scout weekly for adult flies in detritus directly below plants.
2. As soon as fruit starts ripening, collect berries for a Larvae test, choosing berries at the most ripe stages in many sites throughout the field.  Look for berries that look as if they might be infested by SWD such as, soft, sunken areas that may have already been taken over by secondary infection (ie. Botrytis, etc.).  In Blueberries, look for puncture holes in the skin where female SWD may have laid eggs.
3. Through harvest, scout weekly for adults and larvae in and around cull-pilled fruit as well as fruit that is still hanging on the plant. Adults can be monitored by disrupting the fruit in these areas and identifying any flies which are disturbed. Larvae can be monitored by dissecting any fruit, particularly suspect fruit.
4. Effective treatment relies on sufficient canopy coverage and management of the flies that emerge after treatment.
5. Repeat applications may be needed.  With many generations of SWD in a season, the later the season, the more generations and the lower the management threshold.  Scouting for adults and larvae should continue through the end of the harvest season.

Timely Harvesting. It is important to harvest fruit in a timely fashion to avoid susceptibility to SWD. The spotted wing Drosophila appears to prefer ripe fruit.

Field Sanitation. A key to managing SWD is to keep fields as clean of potential fruit hosts as possible. Getting improved fruit handling and cull disposal protocols in place early could mean the difference between a successful season and one that is a disappointment.. Remove any intact, over-ripe, and/or culled fruit from areas in and around the fields.

Adjacent habitat & Urban Site Infestations. Some habitat adjacent to berry fields and some urban sites in Western Oregon and Washington had confirmed, high SWD trap counts in 2010, as well as fruit that was heavily infested with SWD larvae. There is a high probability of ‘hotspots’ in both urban areas and unmanaged habitats that can act as a source for a large number of SWD. From there the flies move into a commercial field when the fruit is at the vulnerable stage. Consider minimizing this source of habitat to avoid introduction or reintroduction of SWD into a commercial field.

For information about chemical controls, check with the Pesticide Guide.