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Spotted Wing Drosophila

The first spotted wing drosophila (SWD) adults this season were collected on traps displayed around fruit crops on May 10 at Chilton Research and Extension Center near Clanton. As of May 23, traps displayed near figs, bunch grapes, blackberries, High Tunnel (HT) grown strawberries, and peaches were positive although at low levels.  Adult numbers ranged from 1 (peaches and blackberries) to 16 SWD per trap on figs (Figure 1).  No adult flies were captured on traps near conventional strawberries.

 

Total adult SWD counts near fruit crops at the CREC, Clanton, May 10-May 23, 2019.

Figure 1. Total adult SWD counts near fruit crops at the CREC, Clanton, May 10-May 23, 2019.

As nearly every small fruit grower knows, SWD is one of the recently emerged most damaging invasive pest species, especially of soft skinned fruit crops.

Description

SWD is similar in size and appearance to Drosophila melanogaster, or so called “vinegar” drosophila. But female SWD preferably lay their eggs in ripe and ripening fruit, unlike nearly all other Drosophila species, which attack rotting fruit. SWD fly has an adult body length of approximately 2-3 mm, red eyes, and yellowish-brown body color. The males are relatively distinctive, as they have a small dark spot on the edge of the wing near the tip, hence the “spotted wing” name (Figure 2A). Females lack the wing spot. The female has a saw-like, serrated ovipositor that enables it to penetrate thin-skinned fruits to deposit its eggs (Figure 2B).

Damage

The resulting larvae feed on the fruit, causing direct damage, and may also be present at harvest, contaminating the product. SWD attack a broad range of fruits, including tree fruits, berry fruits, grapes, and some vegetables. Soft skinned fruit such as raspberries, blackberries, strawberries, and blueberries are the most preferable host plants of SWD. Alabama growers should be alert to the presence of SWD in their area. Monitoring for this pest is an important part of management techniques.

Management

Control is not recommended unless SWD is caught in monitoring traps, fruit injury is detected, or a high-value crop needs protecting. Ripening and ripe fruit are susceptible to SWD attack, but the unripe fruit does not appear to attract them. If adult SWD are present on your farm, aggressive management is warranted that involves:

  1. Use good sanitation and cultural practices to prevent further SWD spread and establishment. Fruit should be harvested early, frequently and completely. Infested fruit that remains in the field allows eggs and larvae to develop fully and, consequently, serves as a source for increased fly populations.
  2. Prune to maintain an open canopy. This may make plantings less attractive to SWD and will facilitate pesticide applications.
  3. Insecticide treatments should be applied at least every seven days and repeated in the event of rain. Effective insecticides with pre-harvest intervals amenable to picking schedules should be selected, and insecticide mode of action should be rotated between each treatment. Visit the Southern Region Small Fruit Consortium IPM website: http://www.smallfruits.org/ipm-guides.html for a list of insecticides registered for use in blueberries, strawberries, caneberries and bunch grapes. Start insecticide applications when you observe SWD, or when your fruit starts to color.

 

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